Because of its inherent fire resistant properties, concrete masonry is often used as a non-structural fire protection covering for structural steel columns. Fire endurance of steel column protection is determined as the period of time for the average temperature of the steel to exceed 1,000 o F (538 o C), or for the temperature at any measured point to exceed 1,200 o F (649 o C) (ref. 1). These criteria depend on the thermal properties of the column cover and of the steel column (ref. 2). Using this technique, an empirical formula was developed to predict the fire endurance of concrete masonry protected steel columns (refs. 3, 4). This formula is presented in Figure 1, and is also included in the International Building Code (ref. 5)
Equivalent Thickness
Equivalent thickness is essentially the solid thickness that would be obtained if the volume of concrete contained in a hollow unit were recast without core holes (see Figure 2). The equivalent thickness is determined in accordance with Standard Methods of Sampling and Testing Concrete Masonry Units, ASTM C 140 (ref. 7), and is reported on the C 140 test report. Note that when all cells of hollow unit masonry are filled with an approved material, such as grout and certain loose fill materials, the equivalent thickness of the assembly is the actual thickness. For more detailed information, as well as typical equivalent thicknesses for concrete masonry units, see Fire Resistance Ratings of Concrete Masonry Assemblies, TEK 07-01D (ref. 8).
REFERENCES
Standard Test Methods for Fire Tests of Building Construction and Materials, ASTM E 119-00. ASTM International, 2000.
Lie, T. T. and Harmathy, T. Z. A Numerical Procedure to Calculate the Temperature of Protected Steel Columns Exposed to Fire, Fire Study No. 28, National Research Council of Canada, March 1972.
Harmathy, T. Z. and Blanchard, J. A. C. Fire Test of a Steel Column of 8-in. H Section, Protected with 4-in. Solid Haydite Blocks, National Research Council of Canada, February 1962.
Lie, T. T. and Harmathy, T. Z. Fire Endurance of Protected Steel Columns, ACI Journal, January 1974.
2006 International Building Code. International Code Council, 2006.
Standard Method for Determining Fire Resistance of Concrete and Masonry Construction Assemblies, ACI 216.1-07/TMS 0216.1-07. American Concrete Institute and The Masonry Society, 2007.
Standard Test Methods for Sampling and Testing Concrete Masonry Units and Related Units, ASTM C 140-02a. ASTM International, 2002.
Fire Resistance Ratings of Concrete Masonry Assemblies, TEK 07-01D. Concrete Masonry & Hardscapes Association, 2018.
Fire safety requires that a wall not only halt the spread of fire from one area to another, but also retain its structural integrity throughout the fire and fire-fighting operations. If occupants, firefighters and building contents are to be fully protected, the structure must not collapse, add fuel to the fire nor emit toxic gases during the fire.
Concrete masonry fire walls provide maximum safety during and after severe fire exposure. Because concrete masonry is a noncombustible structural material which neither adds fuel to a fire nor emits toxic gases, it is widely used to provide compartmentation—containing a fire until it can be brought under control by fire fighters. In addition, even after severe fires, concrete masonry walls can typically be repaired by simply patching cracks and tuckpointing mortar joints, rather than requiring demolition and replacement. Experience with building fires has shown that the most damage to concrete masonry walls during a fire often occurs due to lost support rather than as a direct result of fire on the masonry.
This TEK provides general information on assessment methods and repair techniques and discusses what can be expected after concrete masonry walls have been subjected to fire.
EVALUATING FIRE-EXPOSED WALLS
Preliminary Inspection
After a fire occurs, a preliminary inspection should be conducted as soon as possible to assess: the condition of the structure, the type and severity of problems observed in the affected area(s), the feasibility of rehabilitation and the need for conducting a detailed investigation. After collecting data on the building structure and the fire event, the preliminary investigation should take place as soon as safe entry into the building can be arranged.
The first step in the preliminary investigation is a visual inspection of structural members in the fire-affected areas. Indications of cracking, spalling, deflections, distortions, misalignment of elements and/or exposure of steel reinforcement should be documented. Measurements of deflections, deformations and geometry can be taken of any suspect members for comparison to unexposed members in the same structure. These observations should be recorded, documenting the type of damage and its severity for each affected member. This summary helps identify damaged members in need of more detailed investigation, as well as the extent and nature of any necessary repairs.
As an adjunct to visually assessing the structural members in fire affected areas, the building contents in these areas should be observed. The melting points of various materials (see Table 1) indicate the temperature ranges that have occurred in localized areas, providing an estimate of the maximum temperatures achieved during the fire. These estimated maximum temperatures help establish the severity of the fire relative to the Standard Test Methods for Fire Tests of Building Construction and Materials, ASTM E 119 (ref. 2) fire test, or to another recognized baseline. If the maximum temperatures during the fire are similar to those of the E 119 test, the potential damage to the concrete masonry is somewhat predictable, based on the history of E 119 testing on concrete masonry.
The ASTM E 119 fire test time/temperature protocol is shown in Figure 1.
There is a large body of data on concrete masonry walls tested according to the ASTM E 119 protocol. This test method evaluates walls subjected to the standard test fire. Performance criteria include: resistance to temperature rise on the unexposed side of the wall; resistance to the passage of hot gases or flames through the wall; structural stability during the test; and resistance of the masonry to deterioration under direct exposure to a fire hose stream immediately following the fire test. Research has shown that the fire resistance ratings of concrete masonry walls are invariably determined by the temperature rise on the cold (unexposed) side of the wall.
Field Testing Procedures
Part of the preliminary inspection is determining the need for further testing and evaluation. Nondestructive field tests, such as the use of an impact rebound hammer, are typically not used with concrete masonry, as the hollow cells interfere with obtaining meaningful results in many cases. In addition, extensive field testing is not always prudent, as removal and replacement of the fire-damaged element can sometimes be more economical than extensive testing. A solid understanding of both structural engineering and the effects of fire on building materials is invaluable to this decision-making process. When necessary, destructive test methods can be used to assess the strength of the in-situ concrete masonry (see reference 3). However, nonuniform fire damage on opposite sides of the wall and corresponding strength differences can lead to unreliable results. In most cases, strength testing is unnecessary.
ASSESSING THE CONCRETE MASONRY
In general, structural concrete masonry without excessive deformations, deflections, misalignments or large extensive cracks can typically be repaired rather than replaced. When these types of conditions are present, it indicates that the member’s load-carrying capacity may be impaired, which would require removal and replacement of the suspect members.
Fire distress such as soot and smoke deposits, pitting of aggregates, hairline cracks, shallow spalling and other surface damage generally require only cosmetic repairs. The following sections provide some more detailed guidance on assessing various concrete masonry characteristics after a fire.
Cracks
Cracks wider than about 1/16 in. (1.6 mm) should be further investigated to determine the potential structural impact. When the reinforcing steel in conventionally-reinforced masonry has not been exposed, the load-carrying capacity of the wall can typically be assumed to be relatively unaffected (see also Exposed Reinforcement, below).
Mortar Joint Damage
Mortar joints often appear to be more affected by fire exposure than the adjacent surface of the masonry units. When concrete masonry walls are subjected to a fire hose immediately after fire exposure in ASTM E 119 testing, mortar in the dehydrated state is sometimes flushed out, typically to a depth of about 1/4 in. (6.7 mm). In actual fires, mortar joints subjected to the most severe fire exposures can become softened or chalky, although this damage is typically not deeper than about 3/4 in. (19 mm). However, this loss of mortar does not affect the load-carrying ability of the concrete masonry wall (ref. 4), so can most often be adequately repaired by tuckpointing.
Exposed Reinforcement
Reinforcement exposed during or after a fire must be evaluated for quenching, buckling and/or loss of prestress. The investigator must consider that any exposed steel may have been quenched during fire fighting operations. This rapid cooling causes a loss of ductility in the steel that can reduce the load-carrying capacity of the member. A visual inspection of any exposed structural reinforcement can help asses the potential structural damage. This assessment must be tied to the element under consideration: either a conventionally-reinforced wall or prestressed wall, as follows. In a conventionally-reinforced wall, local buckling of exposed reinforcing bars usually indicates that the steel has been directly exposed to fire. When steel is exposed to temperatures of 1,100 o F (593 o C) or higher, the bars lose about half of their yield strength and buckling occurs. If the bars are exposed but not buckled or otherwise deformed, spalling may have occurred after the fire exposure. In general, flexural reinforcement that is not visibly deformed is unlikely to have suffered significant permanent damage. Similarly, if the spalling does not expose the reinforcement, i.e. the cover protection remains intact, the wall strength is unlikely to be compromised.
In prestressed concrete masonry walls, on the other hand, significant loss of prestress can occur without any visible distress to exposed tendons. Therefore, for prestressed masonry, any exposed prestressing tendons should indicate the need for a more in-depth structural evaluation. Tendon buckling is rarely observed, as the tendon typically remains in tension, even with significant loss of prestress.
EFFECT OF FIRE EXPOSURE ON WALL STRENGTH—EXPERIMENTAL RESULTS
One effect of fire exposure, as determined by testing (ref. 4), was reduced wall compressive strength due to the gradual dehydration of the cement and, depending on the aggregate type, to the expansion and changes in the physical properties of the aggregate used in the concrete masonry units. Reductions in compressive strength for 8-in. (203-mm) units exposed to 3 to 3 1/2 hours of fire varied widely, resulting in maximum reductions of 50 percent for some types of concrete masonry units. Lightweight aggregates, manufactured by expanding certain minerals in a kiln, are stable under fire exposure, so minimize loss of strength. During testing, limestone aggregate concrete masonry units also showed substantial stability and minimized loss of strength after fire exposure (ref. 4). For the wide range of masonry units tested, the wall strength after fire exposure remained directly proportional to the concrete masonry unit compressive strength before fire exposure.
A number of 8-in. (203-mm) walls underwent 2 1/2 to 3 1/2 hours of fire exposure, were cooled, then subjected to another 2 1/2 hour fire before being tested for compressive strength. These results showed that these walls were able to carry the same, or slightly higher, loads as similar walls exposed once for three to four hours, as well as serving as an effective fire barrier during the second fire.
PREPAIRING FIRE-EXPOSED CONCRETE MASONRY
For fire-exposed concrete masonry free from large cracks or deflections, repairs should be minimal. Crack repair and mortar joint tuckpointing procedures and recommendations are covered in detail in Maintenance of Concrete Masonry Walls, TEK 08-01A (ref. 5). Recommended cleaning procedures are covered in Cleaning Concrete Masonry, TEK 08-04A (ref. 6).
SUMMARY
In conventionally-reinforced concrete masonry, if reinforcing steel is not exposed, there is little likelihood of structural damage.
Lintels and beams free from excessive deflections are unlikely to be structurally impaired.
Softening of the top surface of mortar results in little loss of load carrying capacity and can be easily repaired by tuckpointing.
Walls subjected to fire one time without structural damage can be expected to perform just as well in a second fire.
Field tests are typically not conducted to assess fire damaged concrete masonry walls. Post-fire investigation typically consists only of visual inspection.
If no severe distortion, cracking or displacement of concrete masonry walls is present, complete reinstatement of the wall can usually be accomplished by patching cracks and tuckpointing mortar joints.
REFERENCES
Assessing the Condition and Repair Alternatives of Fire-Exposed Concrete and Masonry Members. National Codes and Standards Council of the Concrete and Masonry Industries, August, 1994.
Standard Test Methods for Fire Tests of Building Construction and Materials, ASTM E 119-05. ASTM International, 2005.
Concrete masonry is widely specified for fire walls and fire barriers because it is noncombustible, durable and economical. Although these constructions are ideally continuous, various conditions require joints or penetrations in fire walls and fire and/or smoke barriers, including movement joints, pipe or cable penetrations and electrical wiring and outlets. Regardless of the type of penetrating item, gap or joint, the International Building Code (IBC) (ref. 1) requires that the continuity of the fire-resistant or smoke-resistant assembly be maintained.
A through-penetration firestop system is an assemblage of specific materials or products designed, tested and rated to resist fire spread for a prescribed period of time through openings made in fire resistance-rated walls, floor/ceiling or roof/ceiling assemblies. Firestopping must be installed in accordance with code requirements to maintain fire and life safety.
Choosing an appropriate firestopping system is a key component to a successful installation. The firestop system must be chosen from a building-official-approved listing service. Alternatively, one of the generic listed materials—concrete, mortar or grout—can be used within the limitations of the code.
Various methods are used to maintain continuity where joints, gaps and penetrations exist in fire-resistance-rated masonry construction. For details of control joints for fire-rated concrete masonry construction, refer to the subsequent Joints section and TEK 07-01D, Fire Resistance Ratings of Concrete Masonry Assemblies (ref. 2). Note that materials installed in joints must resist environmental and movement characteristics as specified by the design professional.
MAINTAINING THE CONTINUITY OF THROUGH-PENETRATIONS
The IBC allows several options for extending the fire resistance rating to protect penetrations through fire walls, fire barriers, smoke barrier walls and fire partitions. Section 713.3 of the 2009 IBC (Section 712.3 the 2006 IBC) contains explicit options permitting the use of concrete, mortar or grout to extend the fire rating through the annular space between the penetrating item and the concrete masonry wall provided the following conditions are met (see also Figure 1):
the penetrating item(s) must consist of steel, ferrous, or copper pipes, tubes, or conduits;
the nominal diameter of the penetrating item(s) cannot exceed 6 in. (152 mm);
the opening through the wall cannot exceed 144 in.2 (0.0929 m2); and
the concrete, mortar or grout is permitted where it is installed to the full thickness of the wall or the thickness required to maintain the wall’s fire resistance rating (see TEK 07-01D (ref. 2) for concrete thicknesses required to meet various fire resistance ratings). Note that placement around a penetration with masonry usually requires cutting of units. In the case of rectangular penetrations, continuity can be easily maintained by laying units with the uncut web adjacent to the penetrating item and filling the annular space with mortar
In cases where the penetrating item is contained in a sleeve, the annular space includes the space between the penetrating item and the sleeve as well as the space between the sleeve and wall assembly. Although the mason contractor is responsible for mortaring in the sleeve, filling the annular space between the pipe and the sleeve after the pipe is installed is the responsibility of the firestop contractor, piping contractor, or other firm assigned by the prime contractor or building owner/manager.
The design professional is responsible for assigning fire resistance ratings and smoke resistant assemblies, and specifying the test methods for maintaining continuity of the wall, when required. The mason contractor is not responsible for applying firestop material other than mortar, grout or concrete. The mason simply follows the plan sheet for initial construction by laying up the wall around the penetration, or if appropriate, cutting into a constructed wall. When the limitations for using mortar, grout or concrete indicated above are exceeded, then the firestop contractor, piping contractor or other designated party must apply the appropriate firestop.
If one or more of the above conditions for using mortar, grout or concrete are not met, then the firestop system must be tested in accordance with ASTM E814, Standard Test Method for Fire Tests of Penetration Firestop Systems (ref. 3), UL 1479 Fire Tests of Through Penetration Firestops (ref. 4) (with a minimum positive pressure differential of 0.01 in. (2.49 Pa) of water), or an approved assembly tested in accordance with ASTM E119, Standard Test Methods for Fire Tests of Building Construction and Materials (ref. 5) or a building official-approved alternative per Chapter 1 of the IBC.
ASTM E814 and UL 1479 were developed specifically for through penetrations and cover membrane penetrations as well (see next section, Protecting Membrane Penetrations). Both of these test methods use similar time/temperature curves, and result in a flame rating (F) for the firestop system. The F rating indicates the number of hours the firestop system resisted the passage of fire (during the fire exposure test) or water (during the hose stream test), whichever is lower. The F rating must meet or exceed the required fire resistance rating of the assembly being penetrated.
In addition to the F rating, there are also T (temperature) ratings, L (air, simulating smoke) ratings and, if water resistance is required, W ratings. The T rating indicates the length of time (in hours) it took for the firestop system to heat up on the non-fire exposed side of the assembly to the point where it could cause ignition of combustibles on the unexposed side. This is considered to occur when the temperature on the non-fire-exposed side of the firestop system rises to 325o F (162o C) above the ambient temperature.
It should be noted that in order for a firestop system to obtain a T rating, it must first obtain an F rating. F ratings are required for all firestop systems (except when concrete, mortar or grout are used under the conditions described above), whereas T ratings are not always required.
The L rating is used to maintain the continuity of smoke barriers. UL 1479 is currently the only standard that measures the passage of air through the assembly including the penetrating item, at ambient and at 400o F (204o C). The ambient temperature condition simulates cold smoke, while the 400o F (204o C) condition simulates hot smoke, both measured in cubic feet per minute per square foot of opening area. The lowest L rating is <1 cfm/ft2 (0.005 m3 /s-m2 ). For a penetration assembly in a smoke barrier, the 2006 IBC allows air leakage of 5 cfm/ft2 (0.025 m3 /s-m2 ) of penetration opening at 0.3 in. of water (7.47 Pa) for both the ambient and elevated temperature tests.
PROTECTING MEMBRANE PENETRATIONS
Membrane penetrations, addressed in IBC (2009)section 713.4.1.2, are those which penetrate only a portion of the wall assembly, such as the opening for an electrical outlet. The IBC language for protecting membrane penetrations is very similar to that for through penetrations. However, there are specific prescriptive criteria that address electrical boxes no larger than 16 in.2 (0.0103 m2) in fire walls with a fire resistance rating up to two hours. These criteria address the maximum area of openings, the annular space between the wall and the box, and separation or protection of such boxes when installed on opposite sides of the wall (see Figure 2).
DUCTS
Ducts are addressed in IBC (2009) section 716. Non-dampered ducts that penetrate fire rated walls must comply with the requirements for through penetrations, as described above. Dampered ducts and air transfer openings are tested to either UL 555, Standard for Fire Dampers (ref. 6) or UL 555S, Standard for Smoke Dampers (ref. 7), or both for fire/smoke dampers. Fire and smoke dampers must be tested according to the standards listed above; there are no prescriptive damper treatments that are deemed-to-comply with the IBC.
JOINTS
In Section 714 of the 2009 IBC, any joint in or between fire resistance-rated walls, floor, or floor/ceiling assemblies and roofs or roof/ceiling assemblies is required to provide a fire resistance rating at least equal to that of the wall, floor or roof in or between which it is installed.
The void created at the intersection of an exterior curtain wall assembly and the floor or ceiling assembly must be protected in accordance with IBC Section 714.4.
Fire resistant joint systems must be tested in accordance with the requirements of either ASTM E1966, Standard Test Method for Fire Resistive Joint Systems (ref. 8), or UL 2079, Standard for Tests for Fire Resistance of Building Joint Systems (ref. 9). Control joints not exceeding a maximum width of 0.625 in. (15.9 mm) can be installed if tested to ASTM E119 or UL 263, Standard for Fire Tests of Building Construction and Materials (ref. 10).
Joint systems in smoke barriers must be tested in accordance with the requirements of UL 2079 for air leakage. The air leakage rate of the joint must not exceed 5 cfm per lineal foot of joint (0.00775 m3/s-m) at 0.3 in. of water (7.47 Pa) for both the ambient temperature and elevated temperature tests.
Note that treatments to maintain the fire resistance rating of control joints is also included in ACI 216.1-07/TMS-0216, Code Requirements for Determining Fire Resistance of Concrete and Masonry Construction Assemblies (ref. 11) which is adopted by reference in IBC Section 721.1. These options are also addressed in TEK 07-01D.
Details of concrete masonry fire wall connections to roofs and floors are shown in TEK 05-08B, Detailing Concrete Masonry Fire Walls (ref. 12).
FIRESTOP MATERIAL AND SYSTEMS SELECTION CONSIDERATIONS
When extending the continuity of the wall to and through the penetrating item or items, the appropriate firestop system (or mortar, grout, or concrete) must be selected. Systems selection is the key to appropriate firestopping. Without proper systems selection and installation, the continuity of the fire resistance rated assembly can be compromised.
Several considerations other than fire and smoke need to be accounted for in selecting the firestop system, regardless of the firestop material or assembly type. For example, how much movement is expected in the joint assembly? The firestop system must match the expected movement of the joint to be able to maintain the rated fire resistance. Similarly, any expected movement of the penetrating item must be accommodated. Locking a pipe into a penetration could interfere with the plumbing or piping system performance.
When choosing materials, it is important to note that copper is not compatible with the cement in concrete and may be compromised over time by the mortar, grout or concrete, if used.
For joint systems, there are many configurations of products that make up the firestop ‘system.’ The system may consist of a mineral wool or other backing, packing or damming material, and one of various sealant types including silicone elastomerics, latex or silicone intumescents, latex, or spray system. Plastic piping, insulations, cable trays, and cable penetrating items may have systems comprised of wrap strips, plastic pipe devices, intumescent blocks, and many other products.
A “systems concept” is critical to extending the fire resistance rating and smoke resistant properties of the wall, for both joints and penetrations. In addition, control joint materials must be compatible with the firestop systems selected if the two intersect. The same applies to fire damper assemblies. This compatibility should be verified with both manufacturers. Most importantly, elastomeric control joint materials must allow for the depth of the completed firestop system in the joint. For penetrations, joints or perimeter fire containment, the firestopping must be installed to the tested and listed system in order to be reliable.
Information regarding the Installation, Inspection and Management of Firestop Systems is available at http://www.fcia. org and contained in the FCIA Firestop Manual of Practice (ref. 13). The FCIA Firestop Manual of Practice is free to architects working for design firms, building officials and fire marshals. CMHA does not endorse firestop contractor certification.
MAINTAINING THE FIRE RESISTANCE RATING
The International Fire Code (ref. 14) makes it clear in Section 703.1 that the required fire resistance rating of all fire-resistance rated construction be maintained through proper repair, restoration or replacement as needed. In addition, as building services change, there may be new penetrations required through fire resistance rated concrete masonry assemblies. These new penetrations must also be protected to maintain the integrity of the construction.
Although not required by current building codes, information for on site inspection of firestop systems is provided in ASTM E2174, Standard Practice for On-Site Inspection of Installed Fire Stops (ref. 15) and ASTM E2393, Standard Practice for On-Site Inspection of Installed Fire Resistive Joint Systems and Perimeter Fire Barriers (ref. 16).
REFERENCES
International Building Code. International Code Council, 2006 and 2009.
Fire Resistance Ratings of Concrete Masonry Assemblies, TEK 07-01D. Concrete Masonry & Hardscapes Association, 2018.
Standard Test Method for Fire Tests of Penetration Firestop Systems, ASTM E814-10. ASTM International, Inc., 2010.
Fire Tests of Through-Penetration Firestops, UL 1479. Underwriters Laboratories, 2003.
Standard Test Methods for Fire Tests of Building Construction and Materials, ASTM E119-09c. ASTM International, Inc., 2009.
Standard for Fire Dampers, UL 555. Underwriters Laboratories, 2006.
Standard for Smoke Dampers, UL 555S. Underwriters Laboratories, 1999.
Standard Test Method for Fire-Resistive Joint Systems, ASTM E1966-07. ASTM International, Inc., 2007.
Standard for Tests for Fire Resistance of Building Joint Systems, UL 2079. Underwriters Laboratories, 2004.
Standard for Fire Tests of Building Construction and Materials, UL 263. Underwriters Laboratories, 2003.
Code Requirements for Determining Fire Resistance of Concrete and Masonry Construction Assemblies, ACI 216.1-07/TMS-0216 07. American Concrete Institute and The Masonry Society, 2007.
Detailing Concrete Masonry Fire Walls, TEK 05-08B. Concrete Masonry & Hardscapes Association, 2005.
Firestop Industry Manual of Practice. Firestop Contractors International Association, 2009.
International Fire Code. International Code Council, 2006 and 2009.
Standard Practice for On-Site Inspection of Installed Fire Stops, ASTM E2174-09. ASTM International, Inc., 2009.
Standard Practice for On-Site Inspection of Installed Fire Resistive Joint Systems and Perimeter Fire Barriers, ASTM E2393-10. ASTM International, Inc., 2010.
The application of balanced design principles is particularly important in multifamily residential buildings. The risk of fires in apartments and condominiums is high because of the numerous kitchens, furnaces, hot water heaters, and other causes of residential fires. In addition, there is always a potential for sleeping occupants, children, and others who may be at a disadvantage for evacuating quickly. Fire safety in multifamily housing requires an understanding of the hazards involved, so that both the potential for fire and the threat to life-safety during a fire are minimized. The purpose of balanced design is to protect life and property during a fire. Death and injury from fire is caused by asphyxiation from toxic smoke and fumes; burns from direct exposure to the fire; heart attacks caused by stress and exertion; and impact due to structural collapse, explosion and falls. Life safety in multifamily housing is influenced by the design of the building, its fire protection features, and by the materials, building contents, quality of construction, and maintenance.
BALANCED DESIGN
Balanced design relies on three complementary life safety systems to reduce the risk of death due to fire:
a detection system to warn occupants of a fire
a containment system to limit the extent of fire and smoke
an automatic suppression system to control the fire until it can be extinguished.
Each of these essential systems contributes to lowering the risk of death and injury from fire in multifamily housing. The three balanced design components complement each other by providing fire protection features that are not provided by the other components. Some features of each balanced design component are intended to be redundant, so that in the event that one system is breached, or fails to perform, the other components continue to provide safety.
Although not a tangible element in fire protection, a strong education program should be an integral part of any good fire protection plan in addition to the physical components of a balanced design system.
DETECTION
Accurate early warning is the first line of defense against the slow smoldering fire, typical in dwelling units with a low heat release rate that doesn’t activate a sprinkler head. Detectors that respond to light smoke are important from a life-safety standpoint to alert occupants so they can evacuate.
Other detection or alarm systems may be used to notify the fire department, thus decreasing response time, expediting rescue operations, and limiting the resulting fire spread and property damage. Detectors wired to a central alarm and installed in corridors and common areas notify all building occupants, permit timely and orderly evacuation, and decrease the potential for injury and death.
The National Fire Protection Association (NFPA) National Fire Alarm Code, NFPA 72 (ref. 3), covers minimum performance, location, installation, testing and maintenance of detectors. The Standard includes heat, smoke, flame and gas sensing fire detectors.
The most common detector used in multifamily housing is the smoke sensing fire detector. Detectors should be wired into a continuous power supply. Their location in multifamily housing is determined in accordance with the building code.
Each dwelling unit should be equipped with detectors in all sleeping rooms and in areas adjacent to all sleeping rooms, and on each level of the building, including the basement. The amount of air movement and obstructions within the space, such as partitions, ceiling height, and other factors, will guide the fire protection engineer in the proper selection of the detector location.
The performance of detectors is vulnerable to unpredictable malfunctions, among which are lack of maintenance due to human error and neglect, faulty power supply, and even acts of sabotage by arsonists. Young children, the disabled, elderly, and the deaf may not be able to respond to auditory alarms.
Tests on smoke detectors (ref. 4) indicate the need for a regularly scheduled maintenance and testing program, as well as the periodic replacement of some components.
SUPPRESSION
The function of automatic sprinkler systems is to control a fire at the point of origin. While not designed to extinguish a fire, residential sprinklers have been shown to be very reliable and effective in controlling a fire in the room of origin until it can be extinguished. Sprinklers reduce the likelihood of flashover. Flashover, the rapid ignition of volatile gasses, is particularly hazardous in exit corridors. Suppression of a fire allows access to the building to permit rescue and fire fighting efforts to proceed. Sprinklers are credited with preventing multiple deaths in fires.
The NFPA maintains minimum standards for the design and installation of sprinkler systems. Sprinkler systems for multifamily housing more than four stories in height are covered by NFPA Standard 13 (ref. 1). NFPA Standard 13R (ref. 2) covers the installation of sprinkler systems in multifamily housing up to and including four stories in height. When the interior construction or building contents contain a large amount of combustibles, sprinkler systems should meet the NFPA 13 Standard, regardless of height, to ensure protection in attics, closets, and other concealed spaces built with combustible materials, and to provide additional suppression in all areas due to the higher fuel loadings.
The NFPA Standards cover the design, installation, acceptance testing, and maintenance of sprinkler systems. In addition, there are specific spaces which are not required by NFPA 13R to be sprinklered. The Standards require an adequate water supply and a piping system designed to deliver sufficient water to the sprinkler head. Sprinkler head requirements ensure proper water coverage based on the room dimensions, area to be covered, and fuel loading. The Standards also list exceptions for specific spaces which are not required to be sprinklered. Once installation is complete, the Standards require inspection and acceptance of the system’s piping, valves, pumps and tanks. Testing also includes verification of adequate water flow to the sprinkler heads. After the sprinkler system is in use, it must be maintained; however, specific maintenance requirements and frequency of maintenance are not specified by the Standards.
Performance of automatic sprinklers can be vulnerable to system failures due to inadequate maintenance and inspection, or inadequate water supply. Sprinklers are not intended to control electrical and mechanical equipment fires or fires of external origin, such as fires from adjacent buildings, trash fires, and brush fires. Fires in concealed spaces, including some attics, closets, flues, shafts, ducts, and other spaces where sprinkler heads are not required to be installed, can compromise life safety due to the spread of toxic fumes and smoke. Inadequate water supply can occur due to low pressure in the municipal water system, broken pipes due to earthquakes or excavation equipment, explosions, freezing temperatures, closed valves due to human error, arson or vandalism, corrosion of valves, pump failure due to electrical outage, and lack of system maintenance.
COMPARTMENTATION
Compartmentation contains a fire until it can be brought under control by fire fighters as illustrated in Figure 1. Compartmentation limits the extent of fire by dividing a building into fire compartments enclosed by fire walls or fire separation wall assemblies, and by fire rated floors and ceilings. Compartments also minimize the spread of toxic fumes and smoke to adjacent areas of a building. Conflagrations beyond the fire compartment are prevented by limiting the total fuel load contributing to the fire. Compartmentation provides safe areas of refuge for handicapped, young, elderly, incapacitated and other occupants who may not be capable of unassisted evacuation. Compartmentation also provides safe areas of refuge for extended periods, where evacuation is precluded due to smoke filled exit ways or blocked exits. Compartmented construction provides protection for fire and rescue operations. Highly hazardous areas, such as mechanical, electrical or storage rooms, can be isolated by fire walls from other occupied areas of a building. Fire separation walls and floor/ceiling assemblies between dwelling units in multifamily housing afford protection from fires caused by the carelessness of other occupants.
Each compartment is enclosed by fire resistive components. Floor and wall elements forming the boundaries of each compartment should have a fire resistance rating of at least two hours, and should be constructed of noncombustible materials that are capable of preserving the structural integrity of the building throughout the duration of the fire.
Openings through compartment boundaries should be protected openings. Doors should be self closing when fire or smoke is detected. In multifamily housing, each dwelling unit should form a separate compartment. In addition, interior exit ways, as well as storage, electrical, and mechanical rooms, should be separate compartments. Exterior walls should be fire rated to form a barrier to the penetration of exterior fires and to contain interior fires.
The value of compartmentation could be reduced when joints between floors and walls, typically exterior curtain walls, or between walls and ceilings, are not properly fire-stopped. Damage caused by equipment, abuse, or the installation of utilities which are not properly sealed, can allow the passage of smoke and gas. Unsealed openings around penetrations can also allow the convective spread of smoke. Self-closing mechanisms on doors in compartment walls may fail if not maintained, or if blocked open.
PROPERTY PROTECTION
The initial cost of providing fire safety can be significant; however, balanced design offers advantages which offset initial costs. The higher level of protection for both the structure and its contents limits the potential loss due to fire. Immediate and long term savings will be reflected in lower insurance rates for both the building and its furnishings. Balanced design limits both fire and smoke damage of the building’s contents to the compartment of fire origin. Noncombustible compartment boundaries limit damage to the structure itself and reduce repair time following a fire. Repair is generally nonstructural, but may include the replacement of doors and windows; electrical outlets, switches and wiring; heating ducts and registers; and floor, wall and ceiling coverings.
SUMMARY
Fire protection engineering is as much an art as it is a science. The number of unknowns and potential fire propagation scenarios are numerous. Fire protection is, therefore, generally based more on risk assessment than precise calculation. Currently, building code prescriptive criteria, (ref. 5, 6) along with an understanding of the science of fire protection, guides the designer in addressing fire safety.
Some of the more significant fire safety issues requiring consideration are listed in Table 1, along with the effectiveness of each component of balanced design. As shown by the table, there may be more than one component which is considered effective in mitigating a particular hazard. Since none of the components are fail-safe, overlapping functions are needed to provide the required level of safety. In addition, there are some functions listed in the table which are addressed by only one component of balanced design. The appendix of NFPA Standard 13R (ref. 2) also recognizes the need for compartmentation and detection, along with sprinklers, to ensure a reasonable degree of life-safety protection.
There is a general agreement among the engineering and scientific communities that the desired approach to improving fire safety in buildings is through computer modeling. Limited success to date has been achieved in developing a system (ref. 7) that will assess risk and design protection levels for each of the three components of balanced design. Future efforts will be directed through the government and the private sector in a cooperative effort to develop this tool.
REFERENCES
Installation of Sprinkler Systems, NFPA 13, National Fire Protection Association, 2007.
Standard for the Installation of Sprinkler Systems in Residential Occupancies up to and Including Four Stories in Height, NFPA 13R, National Fire Protection Association, 2007.
National Fire Alarm Code, NFPA 72 National Fire Protection Association, 2007.
Why We Need to Test Smoke Detectors, Leon Cooper, Fire Journal, National Fire Protection Association, November 1986.
Life Safety Code, NFPA 101, National Fire Protection Association, 2006.
Standard on Types of Building Construction, NFPA 220, National Fire Protection Association, 2006.
Fire Hazard Assessment Method, Hazard I, NIST Handbook No. 146, National Institute of Standards and Technology, U.S. Department of Commerce, 1989.
Condensation is one type of moisture to which buildings can potentially be exposed. In addition to above grade precipitates of rain, snow and ice as well as high humidity, several forms of below-grade ground-sourced moisture can also affect building envelopes. Concrete masonry walls are less affected by the problems associated with moisture infiltration and condensate than other building materials (i.e. corrosion, rotting, mold, delamination, blistering and volumetric changes). However, prolonged moisture accumulation can lead to reduced effectiveness of some types of thermal insulation, temporary frost formation and/or efflorescence. Fortunately, these problems can largely be avoided with proper wall design and construction.
Above- and below-grade condensation control strategies include: limiting air leakage and water vapor diffusion, using adequate amounts of thermal insulation, minimizing cold spots, utilizing free draining flashing and weeps, and allowing for drying. Because the condensation potential in a particular assembly can vary with the construction assembly, building type, building usage as well as environmental conditions and seasonal climate changes, however, these strategies may vary from project to project.
CONDENSATION
Warmer air can hold more water in vapor form than can cold air. When warm moist air comes into contact with a cold surface, the air cools and can no longer hold all of its water vapor—the excess moisture condenses.
Local cold spots in a wall can cause small areas of condensation. Cold spots are usually caused either by thermal bridging or by air leakage. Both can be avoided with appropriate design strategies. See TEKs 06-13B Thermal Bridges in Wall Construction and 06-14A Control of Air Leakage in Concrete Masonry Walls (refs. 1, 2) for more detailed information.
Restricting Water Vapor Flow
Water vapor can move through building envelope assemblies by diffusion and via air leakage, so both mechanisms must be considered. The amount of water vapor that travels via air movement can be several orders of magnitude greater than that due to diffusion. Therefore, limiting air leakage is an important water vapor control strategy. For detailed information on reducing air leakage, see TEK 06-14A. When an air barrier material is required, the vapor permeability of the material must be evaluated relative to the material’s location within the wall to help ensure that the air barrier material is not contributing to moisture problems due to vapor diffusion.
Proper design and construction to reduce liquid water entry into wall assemblies will also help reduce condensation potential by reducing moisture surface area and the related water vapor diffusion. The use of moisture tolerant building materials, such as concrete masonry, also reduces the potential damage from condensation and other moisture sources.
A balanced mechanical system backed by an appropriate maintenance program is assumed for optimum efficiency. Supplying draft-controlled make-up air for all exhaust fans reduces air infiltration.
When required, water vapor retarders are used to restrict water vapor diffusion (versus moisture movement due to air leakage). Although the main characteristic of water vapor retarders is vapor permeance, other considerations may include mechanical strength, adhesion, elasticity, thermal stability, fire and flammability resistance, resistance to other deteriorating elements (e.g., chemicals, UV radiation), and ease of application and joint sealing.
A vapor retarder’s effectiveness depends on both its vapor permeance and location within the wall assembly. In addition, because of the large potential for moisture movement with air movement, a vapor retarder in an assembly with high air leakage will be ineffective.
Vapor retarders can limit water vapor movement by diffusion, but can also limit the ability of the assembly to dry. Both results need to be considered in the design. In some cases, using a semi-permeable vapor retarder, or not using a vapor retarder, is recommended to ensure the wall assembly can adequately dry. Other design conditions may dictate the use of a vapor retarder of very low permeance. Each design should be evaluated with the goal of balancing the need to restrict vapor diffusion and the need to allow drying.
Materials are also available that serve as both the vapor retarder and airflow retarder, and are useful when the assessment of air flow control and vapor diffusion control so dictates.
The 2009 International Residential Code (ref. 8) defines three vapor control classes as follows:
Class I: <0.1 perms, such as polyethylene sheet, sheet metal or aluminum facing.
Class II: 0.1 – 1.0 perms, such as kraft faced fiberglass batts, and some vapor control paints.
Class III: 1.0 – 10 perms, such as some latex or enamel paints.
CONDENSATION CONTROL
Condensation control focuses on minimizing airflow through the wall, interrupting water vapor diffusion, maintaining temperatures above the dew point for surfaces exposed to moisture, and allowing for drying.
Condensation can occur in either summer or winter. Design strategies for moisture control (including moisture vapor and humid air) under heating conditions often differ from those for cooling conditions, even though the basic principles of moisture transfer are the same.
In cold climates, moisture tends to be driven from the warm moist interior to the cold dry exterior. Condensation control under these conditions favors strategies that hold the moisture within the insulated envelope. In hot and humid climates, warm moist exterior air is driven towards the cooler drier interior. In this case, the wall should be designed to keep the moisture on the exterior of the wall. Most climates have some combination of the above conditions. In addition, moisture control in certain building types, such as hotels, motels, and cold storage facilities, will often benefit from using the recommendation for warm humid climates, regardless of the building location.
Definitions of climate zones for condensation control are based on the climate zones used in the International Energy Conservation Code (IECC) (ref. 3). The map showing these zones can be found at http://www1.eere.energy.gov/buildings/residential/ba_climate_guidance.html. Climate zones for the United States are: Sub-arctic, very cold, cold, mixed-humid, hot-humid, hot-dry, mixed-dry and marine. These zones are illustrated in Figure 1 for the continental U.S. along with their corresponding IECC climate zones.
Recommendations by Climate Zone
The following sections describe U. S. Department of Energy (DOE) general recommendations (ref. 5) for controlling water vapor movement and allowing drying in new residential construction, based on the climate zones shown in Figure 1.
All recommendations should be considered as part of a comprehensive strategy that addresses items including moisture management (including liquid and vapor, as well as drying potential), energy efficiency, air infiltration and durability.
All Climates
Some recommendations are consistent across all climates:
An air space, such as the properly drained open cores of a single wythe masonry wall or the cavity in a masonry cavity wall, is recommended in all climate zones. The air space provides a drainage plane and allows for better drying. Single wythe masonry walls with completely filled grout spaces will take longer to dry than concrete masonry walls with unfilled cores or a cavity. However, these walls have a large hygroscopic moisture capacity and tend not to be damaged by the longer drying period.
Impermeable interior coverings, such as vinyl wallpaper, are not recommended for exterior walls, because their non-breathable nature tends to trap moisture, inhibit drying and therefore can contribute to mold and mildew within such finishes.
Interior polyethylene vapor retarders are generally not recommended, because they limit the wall’s ability to dry towards the inside. In some cases, these may be mandated by building codes, particularly in wet climates.
In this case, wall assemblies should be carefully designed to accommodate building materials, local climate conditions, and interior moisture loads.
An additional consideration applies to masonry veneers under certain summer conditions. If masonry is not treated for water repellency, water can be absorbed during heavy rains. Subsequent solar heating evaporates some water, raising the water vapor pressure of air in the wall, and potentially causing condensation. This can be prevented by using surface or integral water repellents to restrict wetting of the masonry, or by applying parging or sheathing paper on the exterior side of the insulation.
Cold and Very Cold Climates
Roughly the northern half of the United States experiences a heating dominated climate. Many areas also experience hot summers, however, so both seasons should be considered when designing for condensation control.
In cold and very cold climates, air barriers and vapor retarders are installed on the interior side of the insulation in building envelope assemblies when used. This approach allows the wall assembly to dry towards the exterior, as long as vaporpermeable exterior materials are used. For exterior masonry walls, drywall painted with latex paint (Class III) provides a sufficient vapor retarder.
Hot-Dry & Mixed-Dry Climates
Design considerations for the dry climates tend to focus less on water vapor control and more on issues such as intense solar radiation, brief heavy rains, and managing fire risk. Wall interiors can be painted but not covered with plastic vapor retarders or impervious coatings, such as vinyl wallpaper.
Hot and Humid Climates
Moisture is a significant problem in these climates in terms of both high humidity and high rainfall. Controlling the infiltration of this moisture-laden air into the building envelope and keeping moisture away from cold surfaces are the goals of design and construction in this climate zone.
Ideally in these climates, batt insulation, if used, should be unfaced. However, codes may restrict the use of unfaced batts in wall construction. In addition, because of the susceptibility of batt insulation to moisture, its use is not generally recommended in masonry wall assemblies. Though there are some exceptions, generally all wall interiors and finishes which are part of an insulated masonry wall assembly may be painted or otherwise finished if desired so long as such finishes and assemblies are breathable and permeable as Code and Standards allow. Masonry buildings in Florida have successfully used a non-breathable elastomeric paint on the exterior of the wall to serve as the vapor retarder.
In hot-humid climates the interior space should be dehumidified. Properly sized air-conditioning equipment will help reduce indoor humidity—oversized units should be avoided because they either cycle on and off too frequently or are off for too long a time to effectively dehumidify.
In humid climates, moisture may condense on wall exteriors, because the wall temperature can be below the ambient dew point. Areas such as shaded reentrant building corners are more difficult to dry, since they do not have the benefit of sun and wind for evaporation. In addition, extra care is required for building components prone to thermal bridging, such as walls adjacent to slab or floor edges as well as parapet courses adjacent to roof joists and decks (see Ref. 1 for information on control of thermal bridges).
Mixed-Humid Climates
The mixed-humid climate zone has generally moderate conditions, but can experience very cold winters and hot, humid summers. In these areas, wall assemblies need to be protected from getting wet from both the interior and exterior and should also be allowed to dry to either the exterior or interior.
Perhaps the least costly option is to allow water vapor to “flow through,” by using vapor-permeable building materials on both the interior and exterior. This allows water vapor to diffuse through the assembly from interior to exterior during heating periods and from exterior to interior during cooling periods. If a vapor retarder is used, a semi-permeable (i.e., Class III) vapor retarder on just the interior side is considered adequate. Although the DOE suggests latex paint as an adequate vapor retarder in these climates (ref. 5d), the permeability of latex paints varies with the specific paint and the number and thickness of coats. Consult the manufacturer for specific permeabilities.
Installing vapor retarders on both the interior and exterior to block moisture entry from both directions is not recommended, as any moisture that enters the wall is trapped.
Marine Climates
The marine climate zone also has moderate conditions most of the time, although weather conditions similar to those found in neighboring climate zones occasionally occur. Buildings in the marine climate zone are faced with high interior and exterior moisture loads.
Similar to mixed-humid climates, building assemblies need to be protected from getting wet from both the interior and exterior and should be allowed to dry to either the exterior or the interior. The same wall recommendation apply to marine climates as to mixed humid climates, however, the high moisture loads in the marine climate zone warrant careful consideration of material vapor permeabilities, moisture loads and local climate conditions.
Vapor retarders may be required by building codes, but an option exists for engineered wall designs that do not require vapor retarders to be approved by building officials.
DETERMINING CONDENSATION POTENTIAL
Traditionally, condensation potential has been estimated using steady-state calculations of water vapor pressure and saturation pressures at various points in an assembly. If the calculated vapor pressure exceeds the saturation pressure, condensation is likely to occur if the assumed conditions occur in the field.
This dew point method is a simplified approach which can be used to estimate seasonal mean conditions (rather than daily or even weekly mean conditions) (see Figure 2). However, this method has several disadvantages. For example, wetting and drying cycles cannot be analyzed, since moisture storage within building materials is neglected, as is moisture transfer due to airflow. As a result, the analysis cannot accurately indicate potential damage due to condensation. A complete description of the dew point method is presented in the ASHRAE Handbook, Fundamentals (ref. 6).
Transient computer models which model heat, air and moisture response are an alternative to dew point analyses. They can be used to predict daily or hourly moisture conditions within assemblies. The ASHRAE Handbook, Fundamentals, contains a discussion of input and output parameters, as well as considerations for choosing a program and evaluating the results.
BASEMENTS
Moisture control in basements begins with proper protection from liquid moisture, such as from rain and wet soil. These considerations are addressed in TEK 19-03B, Preventing Water Penetration in Below-Grade Concrete Masonry Walls (ref. 7). If the wall is substantially above grade, condensation control recommendations for the appropriate climate, discussed above, should be followed. If substantially below grade, the basement walls will be dampproofed or waterproofed as required by local code, which essentially acts as an exterior vapor retarder. In this case, an additional interior vapor retarder should be avoided, as this may potentially trap moisture within the wall.
Moisture on the interior of basement walls may be caused by either condensation of interior moisture or leakage of liquid water through the wall. To determine the cause, tape a square of impermeable plastic (such as 6 mil polyethylene) on a portion of the wall experiencing the moisture issues. If there is moisture accumulating under the plastic, an exterior moisture source should be suspected. If moisture forms on top of the plastic, condensation is occurring.
REFERENCES
Thermal Bridges in Wall Construction, TEK 06-13B, Concrete Masonry & Hardscapes Association, 2010.
Control of Air Leakage in Concrete Masonry Walls, TEK 06-14A, Concrete Masonry & Hardscapes Association, 2011.
International Energy Conservation Code. International Code Council, 2009.
Guide to Determining Climate Regions by County, PNNL17211. Pacific Northwest National Laboratory and Oak Ridge National Laboratory, 2010.
Building America Best Practices Series: Builders and Buyers Handbook for Improving New Home Efficiency, Comfort, and Durability. U. S. Department of Energy Building Technologies Program. Available at http://www1.eere.energy.gov/buildings/residential/ba_climate_ guidance.html. 5a. Volume 1, Hot and Humid Climates, NREL/TP-550-36960, 2004. 5b. Volume 2, Hot-Dry and Mixed-Dry Climates, NREL/TP550-38360, 2005. 5c. Volume 3, Cold and Very Cold Climates, NREL/TP-550-38309, 2005. 5d. Volume 4, Mixed-Humid Climates, NREL/TP-550-38448, 2005. 5e. Volume 5, Marine Climates, NREL/TP-550-38449, 2006.
ASHRAE Handbook, Fundamentals. American Society of Heating, Refrigerating, and Air-Conditioning Engineers., Inc., 2009.
Preventing Water Penetration in Below-Grade Concrete Masonry Walls, TEK 19-03B, Concrete Masonry & Hardscapes Association, 2012.
International Residential Code. International Code Council, 2009.
Heat capacity is a material property used to assess a wall’s thermal mass, and it is often used as a criteria in energy codes and standards. Thermal mass is defined as: the absorption and storage of significant amounts of heat in a building or in walls of a building (ref. 1). Wall thermal mass, such as that present in concrete masonry construction, tends to decrease both heating and cooling loads in a given building, thus saving energy. The amount of savings realized by incorporating thermal mass into a building’s design is a function of several variables. These include local climate, wall heat capacity, fenestration (window) area, fenestration orientation, fenestration solar gain, building occupancy load and other internal gains such as lights and office equipment. The most manageable approach to account for energy savings due to thermal mass is to relate the savings to the wall heat capacity and local climate.
Heat capacity (HC) is defined as the amount of heat necessary to raise the temperature of a given mass one degree (refs. 2, 3), and is calculated as the product of a wall’s mass per unit area by its specific heat.
A building with massive walls, such as concrete masonry, often uses less energy for heating and cooling than does one with lightweight frame walls, wood or steel studs for example. Because of this, the International Energy Conservation Code and ASHRAE Standard 90.1, Energy Standard for Buildings Except Low-Rise Residential Buildings (refs. 4, 3), prescribe lower R-value requirements for concrete masonry walls than those for frame walls and metal buildings, in many cases. (This lower required R-value corresponds to a higher required U-factor.) In order to qualify for this lower minimum R-value, ASHRAE Standard 90.1 requires the wall to achieve a minimum HC value. The International Energy Conservation Code defines “mass walls” in terms of wall weight, rather than heat capacity (see reference 5 for detailed information).
This TEK is intended for use by engineers and designers as a guide to determining the heat capacity (HC) of concrete masonry walls.
HEAT CAPACITY VALUES IN CODES AND STANDARDS
ASHRAE Standard 90.1 defines a mass wall as one with a heat capacity exceeding:
7 Btu/ft2 °F (45.2 kJ/m2.K), or
5 Btu/ft2 °F (32.2 kJ/m2.K) provided that the wall has a material unit weight not greater than 120 lb/ft3 (1,922 kg/m3). This criteria clarifies that most lightweight concrete masonry walls are defined as mass walls for the purposes of the Standard.
Walls meeting either of these criteria are considered mass walls, and are eligible to comply to the Standard using the lower mass wall requirements in the prescriptive compliance tables.
In addition to these prescriptive compliance tables, heat capacity is also used in the ENVSTD compliance software, that forms a part of ASHRAE Standard 90.1, when defining a mass wall assembly. See TEKs 06-12E, Concrete Masonry in the 2012 Edition of the IECC, and 06-04B, Energy Code Compliance Using COMcheck (refs. 5, 6) for further information on energy code compliance options.
Concrete masonry heat capacity values are also required for more rigorous energy analyses, such as those necessary to demonstrate compliance with the Total Building Performance option in the International Energy Conservation Code, demonstrate compliance with the Energy Cost Budget Method in ASHRAE Standard 90.1, or demonstrate energy savings to qualify for LEED® program points.
CALCULATING HEAT CAPACITY
Wall heat capacity is defined as: the sum of the products of the mass of each individual material in the wall per unit area times its individual specific heat (ref. 3). As indicated previously, HC is equal to the mass, or wall weight, multiplied by the specific heat. Therefore, for example, a single wythe concrete masonry wall weighing 34 lb/ft 2 (166 kg/m2) has a HC of 7.14 Btu/ft2 · ºF (1.26 kJ/m2.K), as follows:
This simple calculation is based on a rule-of-thumb that the specific heat of most concretes is very close to 0.21 Btu/lb · ºF (880 J/kg. K). The actual value depends on the aggregate type used to manufacture the concrete masonry units. Concrete masonry units produced using sand-gravel aggregates tend to have specific heat values of approximately 0.22 Btu/lb · °F (922 J/kg. K), while most other units have a specific heat of 0.20 to 0.21 Btu/lb · ºF (840 to 880 J/kg. K) (ref. 2).
Single Wythe Walls
Tables 1 through 5 contain calculated heat capacity values for 4-in. to 12-in. (102- to 305-mm) thick concrete masonry walls. The values are based on: minimum face shell and web thickness requirements of Standard Specification for Loadbearing Concrete Masonry Units, ASTM C-90 (ref. 7); 125 pcf (2,003 kg/m3) mortar; and 140 pcf (2,243 kg/m3) grout. For walls not included in these tables, the heat capacity can be calculated by multiplying the wall weight in lb/ft2 (kg/m2) by the specific heat of 0.21 Btu/lb· ºF (880 J/kg. K). Note that concrete masonry wall weights are tabulated in CMU-TEC-002-23, Weights and Section Properties of Concrete Masonry Assemblies (ref. 8).
Multiwythe Walls and Finishes
For multiwythe walls or walls including a finish such as gypsum wallboard or plaster, the heat capacity of the second masonry wythe and/or finish is simply added to that of the first masonry wythe, as follows:
REFERENCES
Guide to Thermal Properties of Concrete and Masonry Systems, ACI 122R-02. American Concrete Institute, 2002.
2005 ASHRAE Handbook, Fundamentals, Chapter 23. American Society of Heating, Refrigerating and Air Conditioning Engineers, Inc., 2005.
Energy Standard for Buildings Except Low-Rise Residential Buildings, ASHRAE 90.1. American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc., 2004 & 2007.
International Energy Conservation Code. International Code Council, 2003 & 2006.
Concrete Masonry in the 2012 Edition of the IECC, TEK 06-12E, Concrete Masonry & Hardscapes Association, 2012.
Energy Code Compliance Using COMcheck, TEK 06-04B, Concrete Masonry & Hardscapes Association, 2012.
Standard Specification for Loadbearing Concrete Masonry Units, ASTM C-90-06b. ASTM International, Inc., 2006.
Weights and Section Properties of Concrete Masonry Assemblies, CMU-TEC-002-23, Concrete Masonry & Hardscapes Association, 2023.
The U.S. Environmental Protection Agency (EPA) estimates that nearly 1 of 15 homes in the United States has elevated indoor levels of radon, the radioactive soil gas which is the second-leading cause of lung cancer (ref. 1). Fortunately, straightforward techniques exist to effectively reduce indoor radon levels.
Four factors contribute to radon entry into buildings: uranium, present in soils throughout the United States; soil permeability, which allows the radon to travel through the soil to the building’s foundation; pathways for radon entry, including cracks and plumbing penetrations; and lower air pressure inside the building, which draws radon inside. Radon-resistant construction techniques focus on controlling the pressure difference between the soil and indoor environment and on minimizing and sealing cracks and penetrations.
Concrete masonry’s versatility and inherent strength and durability characteristics make it especially well-suited for foundation walls . To adequately resist soil gas entry, concrete masonry walls must be designed and constructed to minimize cracking. References 2 through 5 provide excellent information on proper mortar joints, footing construction, wall bracing, backfilling, anchorage, waterproofing and structural design.
This TEK provides basic design guidance specific to radon resistant concrete masonry basement and crawl space construction based on Appendix F of the International Residential Code (IRC) (ref. 6) and EPA guidelines. Although these recommendations have been developed primarily for new low-rise residential construction, the same basic principles also apply to schools and other large buildings.
POTENTIAL FOR ELEVATED RADON LEVELS
It is most cost-effective to install radon-resistant features in homes with the greatest potential for high indoor radon levels. As a tool to help predict where this might occur, the EPA and U.S. Geological Survey have identified areas with high radon potential, based on indoor radon measurements, local geology and population densities (see http://www.epa. gov/radon/zonemap.html). State radon offices should also be consulted for more detailed local information. The EPA does not recommend soil testing as a method to predict the potential for elevated indoor radon levels.
The map assigns a zone number to each U. S. county based on potential indoor radon levels, as follows:
Zone 1: high potential (indoor levels greater than 4 pCi/L)
Zone 2: moderate potential (from 2 to 4 pCi/L)
Zone 3: low potential (less than 2 pCi/L)
BUILDING CODE REQUIREMENTS
The 2003 IRC Appendix F contains radon control methods for new home construction. Note that because these requirements are contained in an appendix, rather than in the body of the code, they become part of the local building code only when Appendix F is specifically adopted by the jurisdiction. The requirements in Appendix F are intended to apply to construction in Zone 1, based on the EPA map described above.
In addition to incorporating radon reduction methods into buildings in Zone 1, or where recommended by state radon offices, the EPA encourages builders to include these techniques in other areas, because high indoor radon levels could potentially occur in any area of the United States, and the installation of a passive venting system is very economical during initial construction, but becomes much more difficult as a post-construction mitigation technique
CONSTRUCTION REQUIREMENTS AND RECOMMENDATIONS
The basic approach to radon control in new buildings incorporates: soil depressurization to vent soil gases outside the building; designing the building’s heating, cooling and ventilation system to provide a slight positive pressure to prevent radon from being drawn inside; and sealing major radon entry routes. Note that several of these requirements are required or considered good practice for issues such as water penetration resistance and/or energy efficiency.
Sealing large openings and preventing large cracks is a key component of building radon-resistant foundations. However, field research has shown that attempting to seal all foundation openings is neither practical nor effective as a stand-alone radon prevention technique (ref. 1).
IRC Appendix F requires installation of a passive depressurization system for the soil beneath a home in Zone 1. This passive depressurization has been found to effectively reduce indoor radon levels by about half and, in most cases, to levels below the EPA action level of 4 pCi/L (ref. 1). Should high indoor radon levels exist with the passive depressurization system in place, the system can easily be upgraded to include an in-line fan to actively draw radon away from the foundation. The IRC includes several requirements that facilitate this possible upgrade. Although not required by the IRC, the EPA recommends that all homes be tested for radon after occupancy, and that mitigation measures be taken with readings at or above 4 pCi/L.
Note that for schools and other large buildings, EPA recommends installing an active depressurization system (i.e., with operational in line fan) during initial construction (ref. 7).
Basement Foundations
Figure 1 illustrates the requirements found in IRC Appendix F for installation of a passive sub-slab venting system for a residential basement. Note that these requirements apply to slab-on-grade foundations as well (see Figure 2).
The system is built on a layer of gas-permeable material, which allows the entire sub-slab area to be vented. The gas-permeable material should be placed under all floors that are in contact with the ground and are within the occupied spaces of the building. The soil gas-retarder membrane serves two purposes: to bridge any cracks that may occur in the slab, thereby preventing radon migration up through the slab at these points; and to prevent concrete as it is being placed from filling the voids in the gas-permeable material. Separate sheets should be lapped at least 12 in. (305 mm), but need not be sealed. In addition, the sheeting should fi t closely around pipes, wires and other penetrations.
The vent pipe extends from the gas-permeable layer to an exhaust point above the roof, allowing any radon that collects below the slab to be removed before it is pulled into the building. IRC Appendix F specifies a minimum vent pipe diameter of 3 in. (76 mm), although the EPA recommends a 4-in. (102-mm) vent pipe diameter to provide better passive venting (ref. 1). As an alternative to the vent pipe location shown in Figure 1, the IRC allows the vent pipe to be inserted directly into an interior perimeter drain tile loop or through a sealed sump cover, provided the sump is exposed to the gas permeable layer or connected to it through a drainage system.
Where interior footings or other barriers interrupt the gas-permeable membrane, each area should have its own vent pipe. These individual vent pipes can be run and exhausted separately, or they can be connected to a single exhaust pipe.
Although the IRC does not stipulate where or how the vent pipe should be run, the EPA offers the following guidance with the goal of inducing a natural upward draft in the vent pipe. The vent pipe should ideally have a vertical run, or, if this is not possible, elbows should be minimized, as these will restrict air flow. In cold climates, the vent pipe should be run in an interior wall. This will help keep the vent pipe warm, enhancing the natural stack effect. Locating the vent pipe in a cold exterior wall could hence make it less effective. In hot climates, the effectiveness of the passive stack depends more on wind, a hot attic and sun heating the pipe (ref. 1). For shallow roofs in hot climates, a higher exhaust point may improve the passive draw through the vent pipe.
The exhaust location requirements listed in Figure 1 help ensure that exhausted radon is not drawn back into the building, or an adjacent building, through a window or other opening.
The solid masonry top course helps resist radon entry from the cells of the masonry units into the habitable space above. This can be accomplished by using 100% solid units or by fully grouting the top course (mesh or other grout-stop device is installed below the course to contain the grout to the top course). Although not required by the IRC, full mortar head joints in this course will also help provide a continuous barrier. When a brick ledge is used, the solid course should be immediately below the brick ledge. As with other parts of the foundation, below grade penetrations and openings must be filled with polyurethane caulk or equivalent.
Several accommodations must be made for possible future fan installation, to convert to an active depressurization system in the event that high radon levels are recorded after occupancy. The first, that the vent pipe remain accessible through the attic or another area outside the habitable space (unless an approved roof-top electrical supply is provided for future use), ensures access for installing an in line fan. The second requirement is for installation of an electrical circuit box at the anticipated vent pipe fan location, typically in the attic, as well as in anticipated locations of system failure alarms.
In addition, IRC Appendix F requires:
all condensate drains must to be trapped or routed through nonperforated pipe to daylight,
sump pits to be covered with a sealed lid,
sumps used as a floor drain to have a lid with a trapped inlet,
ducts passing through or below the slab to be seamless (unless the air-handling system is designed to maintain continuous positive pressure in the ducts),
joints in ducts passing through or below the slab to be sealed,
homes to be constructed to minimize building depressurization, as otherwise required in Section M1601, Chapter 11 and R602.8.
Crawl Space Foundations
Crawl space foundations require preventive measures similar to those for basements, or must be provided with an approved mechanical crawl space ventilation system.
The IRC requirements for passive depressurization in a crawl space are illustrated in Figure 3. The major differences between the crawl space and basement requirements are:
a requirement for natural ventilation per IRC Section R408,
without a slab, it is difficult, if not impossible, to seal radon out at the crawl space floor, so sealing takes place at any penetrations through floors above crawl spaces as well as at access doors and other openings or penetrations between the crawl space and an adjoining basement,
air-handling units located in crawl spaces must be sealed to prevent air from being drawn into the unit, and
ducts in crawl spaces must have seams and joints sealed.
Combination Foundations
Buildings with combination basement/crawl space or slab ongrade/crawl space foundations are required to have a separate radon vent pipe for each foundation area. The vent pipes can either be connected to a single vent that exhausts through the roof, or each can be exhausted separately (ref. 6).
In addition, the EPA recommends that special care be taken at points where the different foundation types meet, because additional soil gas entry routes typically exist at these locations.
REFERENCES
Building Radon Out, EPA/402-K-01-002. Environmental Protection Agency, 2001.
Energy efficiency in buildings has become increasingly important. Whether complying with newer energy codes or gaining recognition for sustainable building practices, reducing the overall energy usage in new and existing buildings continues to be a leading consideration for design teams.
Many methods are employed to increase building energy efficiency. One consideration is reducing air leakage through the building envelope. In addition to the negative impact on a building’s energy efficiency (due to the loss of conditioned air via exfiltration and/or the introduction of unconditioned air via infiltration), air leakage in buildings can also impact moisture control, indoor air quality, acoustics and occupant comfort.
Reduced air leakage is one area where masonry walls excel compared to other wall types when proper design criteria are applied. This TEK reviews available information on masonry wall air leakage, reviews the most recent code criteria, presents concrete masonry wall assemblies that meet this criteria, and provides general guidance on improving the control of air leakage in masonry walls.
AIR LEAKAGE
Air leakage consists of air infiltration from the exterior into the conditioned spaces of buildings and/or exfiltration of conditioned interior air out of buildings. Although under a pressure differential air can pass directly through many materials, air leakage occurs primarily through a myriad of cracks, gaps, improperly designed or constructed joints, utility penetrations, junctions between wall and window and door frames, junctions between wall and roof assemblies, and other avenues.
Historically, air leakage has been the primary source of building ventilation. Because it is uncontrolled and weather-dependent, however, the direct result of air leakage is an increase of energy consumption to maintain space conditioning. Recognition of this increased energy consumption has caused air leakage to be regulated by code for many newer commercial buildings.
Reducing air leakage rates, however, can pose potentially adverse health effects due to stale and polluted air by reducing the air exchanges that dilute contaminants. Mechanical ventilation systems are usually required to satisfy air exchange requirements that have historically been met by uncontrolled air leakage. Although there is an added cost with a designed mechanical ventilation system, it is theoretically offset by the energy savings associated with the reduced air leakage. Heat recovery or energy recovery units (HRV/ERV) can be used to reduce the amount of space conditioning required to condition the fresh air. These systems should be designed carefully, however, as some research shows that the energy consumed by operating the HRV/ERV systems could exceed the cost of conditioning the fresh air (ref. 1).
Studies have shown that air leakage in buildings can be difficult to accurately predict and measure (ref. 2). Prediction and measurement of air leakage rates in walls has been the subject of study by both U.S. and international researchers. U.S. results have focused primarily on the wood stud wall construction with fibrous insulation common to home building. International research has looked at masonry walls as well as wood frame walls, because masonry is the traditional European construction method.
AIR LEAKAGE LOCATIONS
A key issue when addressing air leakage is the significant difference between air leakage at discreet sites, such as at member junctions and at door and window openings where caulking and sealing is at issue, versus the diffuse air leakage that can occur directly through a wall assembly. Chapter 16 of the ASHRAE Fundamentals Handbook (ref. 3) includes the results of residential air leakage studies that show that the largest source of air leakage occurs through wall cracks, joints and utility penetrations. Other major leakage sources include leakage around doors and windows, ceiling penetrations and utility penetrations to the attic, and the HVAC system. The same studies showed that diffusion through walls was less than 1%; i.e., compared to infiltration through holes and other openings, diffusion through walls was not an important flow mechanism in residential buildings. These data are illustrated in Figure 1.
AIR LEAKAGE CRITERIA
To reduce air leakage rates, air barrier systems are sometimes designed and installed as part of the building envelope. Alternatively, the thermal envelope can be designed and detailed to perform as an air barrier system. Current building codes (ref. 4) do not stipulate quantitative requirements for air barriers, but instead require that the exterior envelope be sealed to minimize the infiltration/exfiltration of air through both commercial and residential building envelopes.
The 2012 International Energy Conservation Code (IECC) (ref. 5) and some local jurisdictions, however, have adopted performance requirements for the control of air leakage in commercial buildings. The 2012 IECC provides three levels of compliance, applying to air barrier materials, air barrier assemblies, or the whole building. These commercial air barrier criteria apply only to buildings in Climate Zones 4 through 8. The compliance criteria are (only one of these criteria need to be satisfied):
a building material intended to serve as an air barrier must have an air permeance of less than 0.004 cfm/ft2 at a pressure differential of 1.57 lb/ft2 (0.02 L/s-m2 at 75 Pa),
an assembly of materials intended to serve as an air barrier, such as a concrete masonry wall assembly, must have an air leakage rate of less than 0.04 cfm/ft2 at a pressure differential of 1.57 lb/ft2 (0.2 L/s-m2 at 75 Pa), or
a building must have an air leakage rate of less than 0.4 cfm/ft2 at a pressure differential of 1.57 lb/ft2 (2.0 L/s-m2 at 75 Pa).
Also contained within the code are several “deemed-to-comply” materials and assemblies. The following masonry-related materials and assemblies are included in this list and are therefore considered to comply with the code:
fully grouted concrete masonry (although listed as a material, this compliance option is more accurately deemed an assembly),
as a material, portland cement/sand parge or gypsum plaster with a minimum thickness of 5 /8 in. (16 mm),
as an assembly, portland cement/sand parge, stucco or plaster with a minimum thickness of 1 /2 in. (13 mm), and
concrete masonry walls coated with one application of block filler and two applications of a paint or sealer coating.
The last option is justified based on research completed in the early 2000s. More recent research has documented additional options for materials and coatings to allow concrete masonry assemblies to comply with the maximum assembly air leakage requirement of 0.04 cfm/ft2 at a pressure differential of 1.57 lb/ft2 (0.2 L/s-m2 at 75 Pa). Although not included explicitly in the code, these tested assemblies can be approved under IECC Section 102, Alternate Materials, as meeting the intent of the code. The testing is described in the Masonry Wall Assemblies section below, and the results are summarized in the Guidelines section on page 7.
The 2012 IECC also lists the following materials as acceptable air barrier materials (ref. 5). Any one of these can be used in conjunction with concrete masonry construction, as shown in Figures 2 and 3.
extruded polystyrene insulation board with a minimum thickness of 1/2 in. (13 mm) with joints sealed,
foil-backed polyisocyanurate insulation board with a minimum thickness of 1/2 in. (13 mm) with joints sealed,
closed-cell spray foam insulation with a minimum density of 1.5 pcf (2.4 kg/m3) with a minimum thickness of 1 1/2 in. (36 mm),
open-cell spray foam insulation with a density between 0.4 and 1.5 pcf (0.6 – 2.4 kg/m3) with a minimum thickness of 4 1/2 in. (114 mm), and
gypsum wallboard with a minimum thickness of 1/2 in. (13 mm) with joints sealed.
MASONRY WALL ASSEMBLIES
Multi-Wythe Walls
Multi-wythe concrete masonry assemblies have a variety of options available for compliance with the commercial building air leakage requirements listed above. In addition to the deemed-to-comply options, there are many proprietary air barrier materials and accessories available. Most air barrier materials are some type of coating, which is usually applied to the cavity side of the back up wythe. In addition, some types of spray-applied insulation or rigid insulation (with sealed joints) can be used as an air barrier, as illustrated in Figure 2.
Single Wythe Walls
The available options for single-wythe concrete masonry assemblies are illustrated in Figure 3. Solid grouting is available, as well as coating with a paint, sealer, or block filler. Additionally, exterior wallcoverings and interior wall finishes offer solutions, such as parge coating, stucco, plaster, various insulations and gypsum wallboard. Note that paints, sealers or block fillers are effective when applied to either the interior or exterior surface of the concrete masonry. Hence, when a coating is specified, architectural finishes need not be compromised by the coating.
Concrete Masonry Air Leakage Testing
Research sponsored by CMHA and the NCMA Education and Research Foundation (refs. 6, 7) has documented additional concrete masonry wall assemblies that can meet the air barrier assembly requirements of 0.04 cfm/ft2 at a pressure differential of 1.57 lb/ft2 (0.2 L/s-m2 at 75 Pa). The results are summarized below. See References 6 and 7 for full descriptions of the assemblies and test results.
Commercial-Grade Latex Paint
One project (ref. 6) tested the effects of commercial-grade latex paint on the air leakage rate of concrete masonry wall assemblies. The walls were ungrouted except at the four edges (which were grouted solid to isolate air permeance to a 1 m2 test surface). The research employed a modified ASTM E2178, Standard Test Method for Air Permeance of Building Materials (ref. 8), because there is no standardized test procedure specifically suited for testing concrete masonry assemblies. Three wall sets were built using plain gray concrete masonry units, each with different concrete mix designs, then tested for air leakage.
The wall sections were painted with a typical commercial-grade latex paint (28% solids content by volume), then the air leakage rate was re-measured. The research documented that the air leakage rate decreased as the paint thickness increased: it was determined that the air leakage rate of the wall was inversely proportional to the thickness of the paint applied.
While surface texture was not directly measured in this study, it is believed that the surface texture of smooth-faced concrete masonry units affects the ability of the coating material to develop a continuous coating, which is important for reducing air leakage rates through assemblies.
The results of this research indicate that the air leakage rate of 12-in. (305-mm) concrete masonry walls can be reduced to 0.04 cfm/ft2 or less at a pressure differential of 1.57 lb/ft2 (0.20 L/s-m2 at 75 Pa) by applying between 3.3 and 14.6 mils (0.084 and 0.371 mm) of commercial-grade latex paint for concrete masonry units with a smooth textured surface and a coarse textured surface, respectively.
High-Quality Latex Paint
More recent research (ref. 7) evaluated the effects of four additional coatings: a high-quality latex paint, masonry block filler, water repellent surface coatings, and gypsum wallboard. The concrete masonry units used in this study were also plain gray, medium-weight “utility” type units with a fairly open surface texture (see Figure 4). The use of integral water repellent admixtures was also investigated.
The latex paint used in this project was a high quality retail paint, with a 28% solids content by volume and 47% solids content by weight. To evaluate this paint, a single coat was applied with an average dry film thickness of 1.28 mil (0.033 mm). The paint reduced the air leakage rate by 94%, to a calculated average air leakage rate of 0.011 cfm/ft2 (0.05 L/s-m2), well below the assembly requirement of 0.04 cfm/ft2 (0.2 L/s-m2).
The results indicate that when a high quality latex paint is used, a single coat is all that is necessary to create a continuous coating and provide the required barrier to air flow.
Masonry Block Filler
The block filler evaluated was a water-based masonry primer designed for use on concrete and concrete masonry surfaces. This material is typically used as a base primer coat on concrete and masonry surfaces in preparation for painting. It is a thicker coating material than latex paint, designed to fill pores and surface imperfections in masonry walls. Based on information provided by the manufacturer, this material has a 46% solids content by volume and 55% solids content by weight.
A single coat of block filler was applied with an average dry film thickness of 2.10 mil (0.053 mm). The air leakage rate was reduced by 86% due to the presence of the block filler coating, to 0.011 cfm/ft2 (0.05 L/s-m2). This result is well below the air barrier assembly requirement of 0.04 cfm/ft2 (0.2 L/s-m2).
Gypsum Wallboard
A set of assemblies was also evaluated for air leakage after installing ½ in. (12.7 mm) gypsum wallboard to simulate a single-wythe assembly with a drywall-finished interior.
When the gypsum wallboard was tested by itself, it had an air permeance below the air barrier material requirement of 0.004 cfm/ft2 (0.02 L/s-m2). When the concrete masonry assembly was tested with wallboard attached, it was evident that the performance of the assembly was dominated by the air permeance of the wallboard, as very little air leakage was measured, and the results were below the 0.004 cfm/ft2 (0.02 L/s-m2) requirement for an air barrier material.
Water-Repellent Surface Coatings
Because many single-wythe concrete masonry assemblies use some type of water repellent surface coating, these coatings may be an efficient way to reduce air leakage rates. Both a silane/siloxane and an acrylic microemulsion water repellent coating were evaluated.
While both water repellent coatings reduced the air leakage rate of the assemblies, the reduction was not sufficient to comply with the 2012 IECC air barrier assembly requirements for commercial buildings.
Integral Water Repellents
The effect of an integral water repellent in concrete masonry units and masonry mortar was also evaluated. Integral water repellents in concrete masonry units can improve the compaction of the unit, leading to a slightly tighter concrete matrix and, in some cases, a more uniform surface texture.
The tested set of concrete masonry assemblies contained an integral water repellent admixture at an appropriate dosage to produce water repellent characteristics.
Compared to the assemblies without an integral water repellent, the addition of integral water repellent decreased the air leakage rate by 28% on average. This decrease is likely due to a slightly tighter pore structure resulting from the use of the integral water repellent. The decrease in leakage rate, however, was not sufficient to reduce the assembly air leakage rate to levels that comply with the 2012 IECC.
CONCRETE MASONRY COMPARED TO FRAME CONSTRUCTION
Typical masonry construction does not include some of the leakage sites common in frame walls. Masonry walls do not have sole plates (sills), because the wall is a continuous assembly from the footing up. The top of a masonry wall is typically a tie-beam or bond beam. Trusses or rafters are set to a plate attached to the top course of masonry. Quality caulking and sealing are important at the ceiling finish edge. Sealing is also required at attic access ways, as well as around any wall penetrations.
Commercial Buildings
Measured air leakage rates from existing commercial buildings constructed during or after 1980 have been compiled (ref. 9). From this data, 84% of the masonry buildings included had measured whole-building air leakage rates of less than 2 cfm/ft2 at a pressure differential of 1.57 lb/ft2 (10 L/s-m2at 75 Pa). In comparison, only 30% of frame-walled buildings had measured whole building air leakage rates of less than 2 cfm/ft2 at a pressure differential of 1.57 lb/ft2 (10 L/s-m2 at 75 Pa) (it should be noted that none of these buildings were constructed to meet an air tightness standard). The reported leakage rates were normalized by the above grade area of the building envelope. The data were compiled from various references, and represent a range of climates and building types, making it difficult to draw definite conclusions. The results do indicate, however, that existing masonry buildings tend to have much lower air leakage rates than existing frame-walled buildings.
Residential Buildings
The air leakage rates of masonry walls have also been researched widely in Europe by such groups as the Air Ventilation and Infiltration Center in England (ref. 10). Results from detailed air leakage work performed in Finland show that concrete masonry and lightweight concrete (panelized) walled homes had much lower air leakage rates than wood frame structures (ref. 11). Figure 5 illustrates these differences, comparing older wood frame houses averaging 7.3 air changes per hour (ACH) at 50 Pa to more modern site-built wood frame houses averaging 8.5 ACH, with a very wide range of values. Prefabricated wood element (panelized) houses were better at 6.0 ACH. Both concrete masonry and lightweight concrete houses, however, had roughly one-half the air change rate of the average panelized wood frame homes.
Proper sealing of components into masonry rough openings may be more important than reducing air leakage through masonry assemblies. Dr. Hiroshi Yoshino of Japan’s Tohoku University investigated Japanese housing air leakage (ref. 12) in a broad comparison with data from other nations. He ranked data points from his own research and other investigators into air tightness categories. He observed that some concrete multi-family housing was so air tight that indoor air quality and condensation problems resulted, and ventilation was required. Concrete masonry houses of “air-tight” construction ranked among the best in Japan for air tightness. Several of the other Japanese reports he cited also showed concrete and concrete masonry houses to have lower air leakage rates than typical Japanese frame houses.
Belgian researchers used a sequential technique in masonry homes to examine incremental air leakage measures (ref. 14). Figure 6 shows the progression of air change rates at 50 Pa from “normal construction,” which evidently assumes no air leakage reduction measures, to a masonry wall with all windows, doors and penetrations sealed and weather stripped. Sealing just these items resulted in about 87% less air leakage. The largest improvements are seen after sealing the door and window frames to their respective rough openings, which agrees with the data in ASHRAE (ref. 3). The Belgian findings also agree with a statement in a compendium of European air leakage results which states: “The critical details from the point of view of air-tightness are associated with the (quality of) formation of openings in masonry walls…” (ref. 14).
IMPACTS ON MOISTURE
When an air barrier material is required, its placement can be critical to controlling moisture and hence to wall durability.
First, because air movement can carry a significant amount of moisture into or through a building assembly, and second because the air barrier can act as a vapor retarder. Note that an air barrier is designed to control the movement of air both into and out of the building envelope, whereas a vapor retarder is designed to restrict the diffusion of water vapor through building materials and subsequent condensation. Because a vapor retarder can also inhibit drying, the need for a vapor retarder varies with climate, construction type and building use.
Although the functions of air barriers and vapor retarders differ, in some cases one component can serve both needs. In designs where one material is installed to control both air and water vapor movement, it is important that the material is continuous to provide the required level of air tightness. Where separate airflow and vapor retarders are installed, care must be taken to ensure that the air barrier cannot cause moisture condensation. This can be accomplished through the choice of vapor-permeable materials or through proper placement.
More detailed information on vapor retarders in concrete masonry walls can be found in TEK 06-17B, Condensation Control in Concrete Masonry Walls (ref. 13).
DISCUSSION
Air leakage measurements indicate that properly constructed concrete masonry walls may have better natural resistance to air leakage than typical frame construction. If a further reduction in air leakage rates is required, various options are available. Retrofits for reducing air leakage in concrete masonry construction are straightforward, because fewer dissimilar joints are involved. Also stucco, paints and mastics tend to be less expensive than new sheathing, polymer papers, etc.
GUIDELINES
The following concrete masonry wall assemblies are considered to meet an air leakage of less than 0.04 cfm/ft2 (0.20 L/s-m2) at 75 Pa, either by prescriptive code requirements or as demonstrated through laboratory testing.
By prescriptive IECC criteria (ref. 5):
Fully grouted concrete masonry.
Concrete masonry with a portland cement/sand parge, stucco or plaster with a minimum thickness of 1/2 in. (13 mm).
Concrete masonry walls coated with one application of block filler and two applications of a paint or sealer coating.
By laboratory testing (refs. 6, 8):
12-in. (305-mm) concrete masonry sealed with at least two coats of commercial-grade latex paint.
8-in. (203-mm) concrete masonry coated with a single coat of high quality latex paint.
8-in. (203-mm) concrete masonry coated with a single coat of masonry block filler.
It can be reasonably assumed that compliance would also be achieved by applying these coatings to walls having a larger thickness than those tested.
When coatings such as paint or block filler are called for, they can be applied to either the interior or exterior side of the concrete masonry, so any masonry architectural finishes need not be compromised.
REFERENCES
Sherman, Max H. and Iain S. Walker, LBNL 62341. Energy Impact of Residential Ventilation Norms in the United States, Lawrence Berkeley National Laboratory, 2007.
Carr, D. and J. Keyes, Component Leakage Values and their Relationship to Air Infiltration, Steven Winter Associates, 1984.
2009 ASHRAE Handbook – Fundamentals. American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc., 2009.
International Energy Conservation Code. International Code Council, 2006 and 2009.
International Energy Conservation Code. International Code Council, 2012.
Biggs, David T., Air Permeance Testing of Concrete Masonry Wall Assemblies, FR06. National Concrete Masonry Research and Development Laboratory, January 2008.
Assessment of the Effectiveness of Water Repellents and Other Surface Coatings on Reducing the Air Permeance of Single Wythe Concrete Masonry Assemblies, MR36. Concrete Masonry & Hardscapes Association, 2010.
Standard Test Method for Air Permeance of Building Materials, E2178-03. ASTM International, 2003.
Emmerlich S. J., T. McDowell, W. Anis, Investigation of the Impact of Commercial Building Envelope Airtightness on HVAC Energy Use, NISTIR 7238. National Institute of Standards and Technology, 2005.
Air Ventilation and Infiltration Center, Old Bracknell Lane West, Bracknell, Berkshire, RG12 4AH, Great Britain.
Kohonen, R., S. Ahvenainen and P. Saarnio. Review of Air Infiltration Research in Finland, Air Infiltration Review Vol. 6, No. 1, 1984.
Yoshiro, Dr. H. Overview of Air Infiltration in Japan, Air Infiltration Review. Vol. 5 No. 3, May 1984.
Condensation Control in Concrete Masonry Walls, TEK 06-17B, Concrete Masonry & Hardscapes Association, 2011.
Caluwaerts, P. and P. Nusgens. Overview of Research Work in Air Infiltration and Related Areas in Belgium, Air Infiltration Review. Vol. 5 No. 1, 1983.
Thermal bridging occurs when a relatively small area of a wall, floor or roof loses much more heat than the surrounding area. Thermal bridging can occur in any type of building construction. The effects of thermal bridging may include increased heat loss, occupant discomfort, unanticipated expansion/contraction, condensation, freeze-thaw damage, and related moisture and/or mold problems for materials susceptible to moisture. The severity of the thermal bridge is determined by the extent of these effects.
Thermal bridges, and the subsequent damage, can be avoided by several strategies which are best implemented during the design stage, when changes can be easily incorporated. After construction, repairing thermal bridges can be both costly and difficult.
THERMAL BRIDGING
A thermal bridge allows heat to “short circuit” insulation. Typically, this occurs when a material of high thermal conductivity, such as steel framing or concrete, penetrates or interrupts a layer of low thermal conductivity material, such as insulation. Thermal bridges can also occur where building elements are joined, such as exposed concrete floor slabs and beams that abut or penetrate the exterior walls of a building.
Causes
Thermal bridging is most often caused by improper installation or by material choice/building design. An example of improper installation leading to thermal bridging is gaps in insulation, which allow heat to escape around the insulation and may also allow air leakage. For this reason, insulation materials should be installed without gaps at the floor, ceiling, roof, walls, framing, or between the adjacent insulation materials. Further, insulation materials should be installed so that they remain in position over time.
Although thermal bridging is primarily associated with conduction heat transfer (heat flow through solid materials), thermal bridging effects can be magnified by heat and moisture transfer due to air movement, particularly when warm, moist air enters the wall. For this reason, buildings with typically high interior humidity levels, such as swimming pools, spas, and cold storage facilities, are particularly susceptible to moisture damage. Proper installation of vapor and air retarders can greatly reduce moisture damage caused by thermal bridges. Concrete masonry construction does not necessarily require separate vapor or air retarders: check local building codes for requirements.
Minimizing moisture leakage will also alleviate thermal bridging due to air leakage for two reasons: air will flow through the same points that allow moisture entry; and water leakage can lead, in some cases, to degradation of air barriers and insulation materials.
Effects
Possible effects of thermal bridges are:
increased heat loss through the wall, leading to higher operating costs,
unanticipated expansion and/or contraction,
local cold or hot spots on the interior at the thermal bridge locations, leading to occupant discomfort and, in some cases, to condensation, moisture-related building damage, and health and safety issues,
local cold or hot spots within the wall construction, leading to moisture condensation within the wall, and possibly to damage of the building materials and/or health and safety problems, and/or
local warm spots on the building exterior, potentially leading to freeze-that damage, such as ice dams, unanticipated expansion or contraction, and possible health and safety issues.
Not all thermal bridges cause these severe effects. However, the severity of a particular thermal bridge should be judged by the effect of the thermal bridge on the overall energy performance of the building; the effect on occupant comfort; the impact on moisture condensation and associated aesthetic and/or structural damage; and degradation of the building materials. Appropriate corrective measures can then be applied to the design.
Requirements
ASHRAE Standard 90.1, Energy Standard for Buildings Except Low-Rise Residential Buildings (ref. 1) (included by reference in the International Energy Conservation Code (ref. 2)) addresses thermal bridging in wall, floor and roof assemblies by mandating that thermal bridging be accounted for when determining or reporting assembly R-values and U-factors. For concrete masonry walls, acceptable methods for determining R-values/U-factors that account for the thermal bridging through concrete masonry unit webs include: testing, isothermal planes calculation method (also called series-parallel calculation method), or two-dimensional calculation method. CMHApublished R-values and U-factors, such as those in TEK 06- 01C, R-Values of Multi-Wythe Concrete Masonry Walls, TEK 06-02C, R-Values and U-Factors for Single Wythe Concrete Masonry Walls, and the Thermal Catalog of Concrete Masonry Assemblies (refs. 4, 5, 6), are determined using the isothermal planes calculation method. The method is briefly described in TEK 06-01C as it applies to concrete masonry walls.
SINGLE WYTHE MASONRY WALL
In a single wythe concrete masonry wall the webs of the block and grouted cores can act as thermal bridges, particularly when the cores of the concrete masonry units are insulated. However, this heat loss is rarely severe enough to cause moisture condensation on the masonry surface, or other aesthetic or structural damage. These thermal bridges are taken into account when determining the wall’s overall R-value, as noted above. In severe climates, in certain interior environments where condensation may occur under some conditions, or when otherwise required, the thermal bridging effects can be eliminated by applying insulation on the exterior or interior of the masonry, rather than in the cores. In addition, thermal bridging through webs can be reduced by using a lighter weight masonry unit, or by using special units with reduced web size, or by using units that have fewer cross webs.
Horizontal joint reinforcement is often used to control shrinkage cracking in concrete masonry. Calculations have shown that the effect of the joint reinforcement on the overall R-value of the masonry wall is on the order of 1 – 3%, which has a negligible impact on the building’s energy use.
CONCRETE MASONRY CAVITY WALL
In masonry cavity walls, insulation is typically placed between the two wythes of masonry, as shown in Figure 1. This provides a continuous layer of insulation, which minimizes the effects of thermal bridging (note that some references term the space between furring or studs as a “cavity,” which differs from a masonry cavity wall).
Because the wall ties are isolated from the interior, the interior surface of the wall remains at a temperature close to the building’s interior temperature. The interior finish material is not likely to be damaged due to moisture condensation, and occupant comfort is not likely to be affected. As with horizontal joint reinforcement in single wythe construction, the type, size, and spacing of the ties will affect the potential impact on energy use.
MASONRY VENEER WITH STEEL STUD BACKUP
Figure 2 shows a cross section of a typical concrete masonry veneer over a steel stud backup. Steel studs act as strong thermal bridges in an insulated wall system. Almost 1,000 times more heat flows through the steel than through mineral fiber insulation of the same thickness and area. The steel stud allows heat to bypass the insulation, and greatly reduces the insulation’s effectiveness.
Just as for concrete masonry webs, the thermal bridging through steel studs must be accounted for. According to ASHRAE Standard 90.1, acceptable methods to determine the R-value of insulated steel studs are: testing, modified zone calculation method, or using the insulation/framing layer adjustment factors shown in Table 1. The effective framing/cavity R-value shown in Table 1 is the R-value of the insulated steel stud section, accounting for thermal bridging. Using these corrected R-values allows the designer to adequately account for the increased energy use due to the thermal bridging in these wall assemblies.
Table 1 shows that thermal bridging through steel studs effectively reduces the effective R-value of the insulation by 40 to 69 percent, depending on the size and spacing of the steel studs and on the R value of the insulation.
Because the steel studs are typically in contact with the interior finish, local cold spots can develop at the stud locations. In some cases, moisture condenses causing dampness along these strips. The damp areas tend to retain dirt and dust, causing darker vertical lines on the interior at the steel stud locations. If warm, moist indoor air penetrates into the wall, moisture is likely to condense on the outer flanges of the steel studs, increasing the potential for corrosion of studs and connectors and structural damage of the wall. Gypsum sheathing on the exterior of the studs can also be damaged due to moisture, particularly during freeze-thaw cycles. These impacts can be minimized by including a continuous layer of insulation over the steel stud/insulation layer.
SLAB EDGE & PERIMETER BEAM
Another common thermal bridge is shown in Figure 3. When this wall system is insulated on the interior, as shown on the left, thermal bridging occurs at the steel beam and where the concrete floor slab penetrates the interior masonry wythe.
A better alternative is to place insulation in the cavity, as shown on the right in Figure 3, rather than on the interior. This strategy effectively isolates both the slab edge and the steel beam from the exterior, substantially reducing heat flow through these areas and condensation potential, and decreasing heating loads (ref. 3).
A third alternative, not illustrated, is to install insulation on the interior of the steel beam. This solution, however, does not address the thermal loss through the slab edge. In addition, the interior insulation causes the temperature of the steel beam to be lower, and can lead to condensation unless a tight and continuous vapor retarder is provided.
MASONRY PARAPET
Because a parapet is exposed to the outside environment on both sides, it can act as a thermal fin, wicking heat up through the wall. Figure 4 shows two alternative insulation strategies for a masonry parapet. On the left, even though the slab edge is insulated, the parapet is not. This allows heat loss between the roof slab and the masonry backup.
A better alternative is shown on the right in Figure 4. Here, the parapet itself is insulated, maintaining a thermal boundary between the interior of the building and the outdoor environment. This significantly reduces heating and cooling loads, and virtually eliminates the potential for condensation on the underside of the roof slab.
REFERENCES
Energy Standard for Buildings Except Low-Rise Residential Buildings ASHRAE Standard 90.1. American Society of Heating, Refrigerating, and Air-Conditioning Engineers, 2004 and 2007.
International Energy Conservation Code. International Code Council, 2006 and 2009.
ASHRAE Handbook—HVAC Applications. American Society of Heating, Refrigerating, and Air-Conditioning Engineers, 2007.
R-Values of Multi-Wythe Concrete Masonry Walls, TEK 06-01C, Concrete Masonry & Hardscapes Association, 2013.
R-Values and U-Factors for Single Wythe Concrete Masonry Walls, TEK 06-02B, Concrete Masonry & Hardscapes Association, 2013.
The variety of concrete masonry wall constructions provides for a number of insulating strategies, including: interior insulation, insulated cavities, insulation inserts, foamed-in-place insulation, granular fills in block core spaces, and exterior insulation systems. Each masonry wall design has different advantages and limitations with regard to each of these insulation strategies. The choice of insulation will depend on the desired thermal properties, climate conditions, ease of construction, cost, and other design criteria. Note that insulation position within the wall can impact dew point location, and hence affect the condensation potential. See TEK 06-17B, Condensation Control in Concrete Masonry Walls (ref. 1) for more detailed information. Similarly, some insulations can act as an air barrier when installed continuously and with sealed joints. See TEK 06-14B, Control of Infiltration in Concrete Masonry Walls, (ref. 2) for further information.
MASONRY THERMAL PERFORMANCE
The thermal performance of a masonry wall depends on its steady state thermal characteristics (described by R-value or U-factor) as well as the thermal mass (heat capacity) characteristics of the wall. The steady state and mass performance are influenced by the size and type of masonry unit, type and location of insulation, finish materials, and density of masonry. Lower density concrete masonry mix designs result in higher R-values (i.e., lower U-factors) than higher density concretes. Thermal mass describes the ability of materials to store heat. Because of its comparatively high density and specific heat, masonry provides very effective thermal storage. Masonry walls remain warm or cool long after the heat or airconditioning has shut off. This, in turn, effectively reduces heating and cooling loads, moderates indoor temperature swings, and shifts heating and cooling loads to off-peak hours. Due to the significant benefits of concrete masonry’s inherent thermal mass, concrete masonry buildings can provide similar performance to more heavily insulated frame buildings.
The benefits of thermal mass have been incorporated into energy code requirements as well as sophisticated computer models. Energy codes and standards such as the International Energy Conservation Code (IECC) (ref. 5) and Energy Efficient Standard for Buildings Except Low-Rise Residential Buildings, ASHRAE/IESNA Standard 90.1 (ref. 6), permit concrete masonry walls to have less insulation than frame wall systems to meet the energy requirements.
Although the thermal mass and inherent R-value/U-factor of concrete masonry may be enough to meet energy code requirements (particularly in warmer climates), concrete masonry walls often require additional insulation. When they do, there are many options available for insulating concrete masonry construction. When required, concrete masonry can provide walls with R-values that exceed code minimums (see refs. 3, 4). For overall project economy, however, the industry suggests a parametric analysis to determine reasonable insulation levels for the building envelope elements.
The effectiveness of thermal mass varies with factors such as climate, building design and insulation position. The effects of insulation position are discussed in the following sections. Note, however, that depending on the specific code compliance method chosen, insulation position may not be reflected in a particular code or standard.
There are several methods available to comply with the energy requirements of the IECC. One of the options, the IECC prescriptive R-values (IECC Table 502.2(1)) calls for “continuous insulation” on concrete masonry and other mass walls. This refers to insulation uninterrupted by furring or by the webs of concrete masonry units. Examples include rigid insulation adhered to the interior of the wall with furring and drywall applied over the insulation, continuous insulation in a masonry cavity wall, and exterior insulation and finish systems. If the concrete masonry wall will not include continuous insulation, there are several other options to comply with the IECC requirements—concrete masonry walls are not required to have continuous insulation in order to meet the IECC. See TEK 06-12E, Concrete Masonry in the 2012 Edition of the IECC and TEK 06-04B, Energy Code Compliance Using COMcheck (refs. 7, 8).
INTERIOR INSULATION
Interior insulation refers to insulation applied to the interior side of the concrete masonry, as shown in Figure 1. The insulation may be rigid board (extruded or expanded polystyrene or polyisocyanurate), closed-cell spray polyurethane foam, cellular glass, fibrous batt, or fibrous blown-in insulation (note, however, that fibrous insulation is susceptible to moisture). The interior wall surface is usually finished with gypsum wallboard or paneling.
Interior insulation allows for exposed masonry on the exterior, but isolates the masonry from the building’s interior and so may reduce the effects of thermal mass.
With rigid board insulation, an adhesive is used to temporarily hold the insulation in place while mechanical fasteners and a protective finish are applied. Furring may be used and held away from the face of the masonry with spacers. The space created by the spacers provides moisture protection, as well as a convenient and economical location for additional insulation, wiring or pipes.
As an alternative, wood or metal furring can be installed with insulation placed between the furring. The furring size is determined by the type of insulation and R-value required. Because the furring penetrates the insulation, the furring properties must be considered in analyzing the wall’s thermal performance. Steel penetrations through insulation significantly affect the thermal resistance by conducting heat from one side of the insulation to the other. Although not as conductive as metal, the thermal resistance of wood and the cross sectional area of the wood furring penetration should be taken into account when determining overall R-values. See TEK 06-13B, Thermal Bridges in Wall Construction (ref. 9) for more information.
Closed cell spray polyurethane foam is typically installed between interior furring. The foam is applied as a liquid and expands in-place. Proper training helps ensure a quality installation. The foam is resistant to both air and water vapor transmission.
When using interior insulation, concrete masonry can accommodate both vertical and horizontal reinforcement with partial or full grouting without interrupting the insulation layer. The durability, weather resistance, and impact resistance of the exterior of a wall remain unchanged with the addition of interior insulation. Impact resistance on the interior surface is determined by the interior finish.
INTEGRAL INSULATION
Figure 2 illustrates some typical integral insulations in single-wythe masonry walls. Integral insulation refers to insulation placed between two layers of thermal mass. Examples include insulation placed in concrete masonry cores and continuous insulation in a masonry cavity wall (note that an insulated masonry cavity wall can also be considered as exterior insulation if the thermal mass effect of the veneer is disregarded).
With integral insulation, some of the thermal mass (masonry) is directly in contact with the indoor air, which provides excellent thermal mass benefits, while allowing exposed masonry on both the exterior and interior.
Multi-wythe cavity walls contain insulation between two wythes of masonry. The continuous cavity insulation minimizes thermal bridging. The cavity width can be varied to achieve a wide range of R-values. Cavity insulation can be rigid board, closed cell spray polyurethane foam, or loose fill. To further increase the thermal performance, the cores of the backup wythe may be insulated.
When rigid board insulation is used in the cavity, the inner masonry wythe is typically completed first. The insulation is precut or scored by the manufacturer to facilitate placement between the wall ties. The board insulation may be attached with an adhesive or mechanical fasteners. Tight joints between the insulation boards maximize the thermal performance and reduce air leakage. In some cases, the joints between boards are set into an expandable bead of sealant, or caulked or taped to act as an air barrier.
Integral insulations placed in masonry cores are typically molded polystyrene inserts, foams, or expanded perlite or vermiculite granular fills. As for the furring used for interior insulation, the thermal resistance of the concrete masonry webs and any grouted cores should be accounted for when determining the thermal performance of the wall (see TEK 06-02C, ref. 3, for tabulated R-values of walls with core insulation). When using core insulation, the insulation should occupy all ungrouted core spaces (although some rigid inserts are configured to accommodate reinforcing steel and grout in the same cell).
Foamed-in-place insulation is installed in masonry cores after the wall is completed. The installer either fills the cores from the top of the wall or pumps the foam through small holes drilled into the masonry. Foams may be sensitive to temperature, mixing conditions, or other factors. Therefore, manufacturers’ instructions should be carefully followed to avoid excessive shrinkage due to improper mixing or placing of the foam.
Polystyrene inserts may be placed in the cores of conventional masonry units or used in specially designed units. Inserts are available in many shapes and sizes to provide a range of R-values and accommodate various construction conditions. In pre-insulated masonry, the inserts are installed by the manufacturer. Inserts are also available which are installed at the construction site.
Specially designed concrete masonry units may incorporate reduced height webs to accommodate inserts in the cores. Such webs also reduce thermal bridging through masonry, since the reduced web area provides a smaller cross-sectional area for heat flow through a wall. To further reduce thermal bridging, some manufacturers have developed concrete masonry units with two cross webs rather than three.
Vertical and horizontal reinforcement grouted into the concrete masonry cores may be required for structural performance. Cores to be grouted are isolated from cores to be insulated by placing mortar on the webs to confine the grout. Granular or foam insulation is placed in the ungrouted cores within the wall. Thermal resistance is then determined based on the average R-value of the wall area (see TEK 06-02C, ref. 3, for an explanation and example calculation). Some rigid inserts are configured to accommodate reinforcing steel and grout, to provide both thermal protection and structural performance. When inserts are used in grouted construction, the coderequired minimum grout space dimensions must be met (see TEK 03-02A, ref. 10).
Granular fills are placed in masonry cores as the wall is laid up. Usually, the fills are poured directly from bags into the cores. A small amount of settlement usually occurs, but has a relatively small effect on overall performance. Granular fills tend to flow out of any holes in the wall system. Therefore, weep holes should have noncorrosive screens on the interior or wicks to contain the fill while allowing water drainage. Bee holes or other gaps in the mortar joints should be filled. In addition, drilled-in anchors placed after the insulation require special installation procedures to prevent loss of the granular fill.
EXTERIOR INSULATION
Exterior insulated masonry walls are walls that have insulation on the exterior side of the thermal mass. In these walls, continuous exterior insulation envelopes the masonry, minimizing the effect of thermal bridges. This places the thermal mass inside the insulation layer. Exterior insulation keeps masonry directly in contact with the interior conditioned air, providing the most thermal mass benefit of the three insulation strategies.
Exterior insulation also reduces heat loss and moisture movement due to air leakage when joints between the insulation boards are sealed. Exterior insulation negates the aesthetic advantage of exposed masonry. In addition, the insulation requires a protective finish to maintain the durability, integrity, and effectiveness of the insulation.
For exterior stucco installation, a reinforcing mesh is applied to reinforce the finish coating, improving the crack and impact resistance. Fiberglass mesh, corrosion-resistant woven wire mesh or metal lath is used for this purpose. After the mesh is installed, mechanical fasteners are placed through the insulation, to anchor securely into the concrete masonry. Mechanical fasteners can be either metal or nylon, although nylon limits the heat loss through the fasteners.
After the insulation and reinforcing mesh are mechanically fastened to the masonry, a finish coating is troweled onto the surface. This surface gives the wall its final color and texture, as well as providing weather and impact resistance.
BELOW GRADE APPLICATIONS
Below grade masonry walls typically use single-wythe wall construction, which can accommodate interior, integral, or exterior insulation.
Exterior or integral insulation is effective in moderating interior temperatures and in shifting peak energy loads. The typical furring used for interior insulation provides a place to run electric and plumbing lines, as well as being convenient for installing drywall or other interior finishes.
When using exterior or integral insulation strategies, architectural concrete masonry units provide a finished surface on the interior. Using smooth molded units at the wall base facilitates screeding the slab. After casting the slab, a molding strip, also serving as an electric raceway, can be placed against the smooth first course. The remainder of the wall may be constructed of smooth, split-face, split ribbed, ground faced, scored or other architectural concrete masonry units.
Insulation on the exterior of below grade portions of the wall is temporarily held in place by adhesives until the backfill is placed. That portion of the rigid board which extends above grade should be mechanically attached and protected.
REFERENCES
Condensation Control in Concrete Masonry Walls, TEK 06-17B, Concrete Masonry & Hardscapes Association, 2011.
Control of Infiltration in Concrete Masonry Walls, TEK 06-14A, Concrete Masonry & Hardscapes Association, 2011.
R-Values and U-Factors of Single Wythe Concrete Masonry Walls, TEK 06-02C, Concrete Masonry & Hardscapes Association, 2013.
R-Values of Multi-Wythe Concrete Masonry Walls, TEK 06-01C, Concrete Masonry & Hardscapes Association, 2013.
International Energy Conservation Code. International Code Council, 2003, 2006 and 2009.
Energy Efficient Standard for Buildings Except LowRise Residential Buildings, ASHRAE/IESNA Standard 90.1. American Society of Heating, Refrigerating and Air Conditioning Engineers and Illuminating Engineers Society, 2001, 2004 and 2007.
International Energy Conservation Code and Concrete Masonry, TEK 6-12C. Concrete Masonry & Hardscapes Association, 2007.
Energy Code Compliance Using COMcheck TEK 06-04B, Concrete Masonry & Hardscapes Association, 2012.
Thermal Bridges in Wall Construction, TEK 06-13B, Concrete Masonry & Hardscapes Association, 2010.
