Resources

Foam Plastic Insulation in Concrete Masonry Walls

November 2018

INTRODUCTION

Foam plastic insulation is often used in exterior concrete masonry construction to improve steady state thermal performance (R-values), and in some cases to improve air and moisture infiltration properties as well. Because of their potential flammability and smoke generation in case of fire, the International Building Code (IBC) (ref. 1) imposes additional requirements on these materials when they are used in exterior walls. These requirements are covered in IBC section 2603.

Foam plastic insulations include both rigid board (expanded polystyrene, extruded polystyrene, polyisocyanurate) as well as open cell and closed-cell spray-applied or foamed-in-place insulations. They may be used on the interior, exterior or in the cores (as either inserts or foamed-in-place) of single wythe masonry walls, and in the cavities of masonry cavity walls.

Because these plastics are flammable, the IBC mandates that they be protected by fire-resistance-rated materials or assemblies in wall and roof assemblies, to prevent the plastic insulation from contributing to the spread of fire in a building.

This TEK describes the IBC requirements for assemblies containing foam plastic insulation and presents details of concrete masonry walls that comply with those requirements. Note that this TEK focuses on the requirements for masonry wall assemblies: there may be additional requirements for the insulation, such as flame spread index and labeling.

IBC REQUIREMENTS

IBC Section 2603 regulates the use of foam plastic insulation in all types of construction, both combustible and noncombustible, with the intent of limiting the spread of fire via these materials. For exterior walls, Section 2603 requires:

a thermal barrier between foam plastic insulation and the building interior, which can be satisfied with a 1 in. (25 mm) minimum thickness of concrete or masonry,
ignition testing for foam plastic insulations applied to wall exteriors, although assemblies protected with at least 1 in. (25 mm) of concrete or masonry on the exterior are exempt from testing, and
successful testing in accordance with NFPA 285, Standard Fire Test Method for Evaluation of Fire Propagation Characteristics of Exterior Non-Load-Bearing Wall Assemblies Containing Combustible Components (ref. 2).

Note that there are two important exceptions to the requirement for NFPA 285 testing:

Wall assemblies where the foam plastic insulation is covered on each face by a minimum 1 in. (25 mm) thickness of masonry or concrete and meeting one of the following:
a) there is no air space between the insulation and the concrete or masonry (as occurs with foamed-in-place insulation); or
b) the insulation has a flame spread index of 25 or less as determined by ASTM E84, Standard Test Method for Surface Burning Characteristics of Building Materials, or UL 723, Standard for Test for Surface Burning Characteristics of Building Materials, (refs. 3, 4) and the air space between the insulation and the concrete or masonry does not exceed 1 in. (25 mm).
One-story buildings meeting the following conditions: foam plastic with a flame spread index of 25 or less and a smoke-developed index of 450 max can be placed in exterior walls without a thermal barrier where it is covered with aluminum (at least 0.032 in. (0.813 mm) thick) or corrosion-resistant steel (at least 0.0160 in. (0.406 mm) thick), provided that the insulation is not thicker than 4 in. (102 mm), and that the building is equipped with an automatic sprinkler system.

Wall assemblies meeting the requirements listed under number 1 above and buildings meeting the requirements listed under number 2 are deemed to comply with the Section 2603 requirements. Note that in cases where there is less than 1 in. (25 mm) of masonry over the insulation, there are insulations available that will meet the NFPA 285 requirements.

NFPA 285 REQUIREMENTS

NFPA 285 addresses the possibility of fire entering wall cavities through door or window openings, igniting foam plastic insulation and spreading vertically to upper stories.

The test evaluates exterior wall assemblies for buildings required to have exterior walls of noncombustible construction. The test provides a method of determining the flammability characteristics of exterior nonloadbearing wall assemblies. It is intended to evaluate combustible components included within wall assemblies required to be noncombustible, under conditions of a fire originating in the building interior.

NFPA 285 evaluates four conditions:

flame propagation over the exterior face;
flame propagation within combustible components from one story to the next;
vertical flame propagation on the interior wall surface from one story to the next; and
lateral flame propagation from one compartment to the next.

To evaluate these conditions, a two-story wall assembly with a window opening on the first floor is constructed in the test assembly. After a 30-minute fire exposure with the burner in the window opening, recorded temperatures are compared to the Standard’s conditions of acceptance to determine compliance. Note that the test evaluates wall assemblies, not specific materials.

SINGLE WYTHE CONCRETE MASONRY WALLS

Single wythe walls may incorporate foam insulation in the cores of the masonry units as either rigid foam inserts or foamed in-place insulation. As discussed above, IBC Chapter 26 essentially requires a minimum of 1 in. (25 mm) of concrete or masonry on the interior and exterior of the foam insulation, as well as protection at headers to prevent ignition of the insulation above door and window openings.

When placed in concrete masonry cores, the foam plastic insulation is protected on the interior and exterior by the concrete face shells. Minimum face shell thickness for concrete masonry units is governed by ASTM C90, Standard Specification for Loadbearing Concrete Masonry Units, (ref. 5) as listed in Table 1. Table 1 shows that concrete masonry units of 6-in. (152 mm) thickness or greater provide the IBC-required 1 in. (25 mm) interior and exterior protection. Because of the small core size of 4-in. (102-mm) units, the cores of these units are rarely insulated. When insulation is placed in the cells of concrete masonry units and bond beams are provided at each story and lintels over each opening, the insulation is fully encapsulated. This meets the intent of the code to prevent the propagation of fire within wall cavities and no further isolation is necessary in this case.

In single wythe construction, door and window headers are typically constructed using either a reinforced precast lintel or a reinforced concrete masonry lintel (shown in Figure 1). This detail provides concrete cover well over the 1 in. (25 mm) minimum required by Section 2603. The detail and level of protection would be similar with a precast concrete lintel. Refer to TEK 19-02B, Design for Dry Single Wythe Concrete Masonry Walls (ref. 6), for additional details on flashing single wythe walls.

MULTI-WYTHE WALLS

Multi-wythe concrete masonry construction is most commonly masonry cavity walls, which often incorporate foam plastic insulation in the cavity formed by the two masonry wythes. In this case, there is more than 1 in. (25 mm) of masonry on both the interior and exterior, so the focus for protecting the insulation is on the headers and jambs of window and door openings.

Per Building Code Requirements for Masonry Structures (ref. 8) concrete masonry veneer walls are to have a minimum specified 1 in. (25 mm) air space with special precautions to limit mortar overhangs inside the cavity to allow adequate drainage between the wythes. Exception b to NFPA 285 testing (see page 1) limits the air space between the insulation and the masonry to 1 in. (25 mm) maximum. Therefore, when exception b is being used, the designer should specify a 1 in. (25 mm) air space to meet both requirements.

Figure 3 shows a window top of opening detail in a concrete masonry cavity wall. In this case, 1 in. (25 mm) of mortar is slushed into the cavity below the insulation to provide the required level of protection. In addition, testing (refs. 7, 10) has shown that mineral wool fire safing covering insulation board exposed at openings in a masonry cavity wall is sufficient to pass NFPA 285 requirements. Note that mineral wool insulation cannot be exposed to the moisture in the drainage cavity. If used, it must be behind flashing or similarly protected.

The jambs of metal doors (see Figure 4) are typically filled with mortar as the wall is constructed, again providing adequate protection for the insulation.

For wood door jambs, several options are shown in Figures 5 and 6. Figure 5 shows a detail where the insulation is held 1 in. (25 mm) back from the jamb. An additional piece of insulation bridges the cavity and acts as a backer for a 1 in (25 mm) layer of mortar. Another option is shown in Figure 6, where the unit adjacent to the jamb is turned 90o, and the unit is cut so that part of the face shell extends across the cavity, between the jamb and the insulation. On the alternate courses, a piece of the cut face shell can be mortared across the cavity to provide the protection. Wood window jamb details are very similar, as shown in Figures 7 and 8.

REFERENCES

International Building Code. International Code Council, 2015.
Standard Fire Test Method for Evaluation of Fire Propagation Characteristics of Exterior Non-Load-Bearing Wall Assemblies Containing Combustible Components, NFPA 285. National Fire Protection Association, 2012.
Standard Test Method for Surface Burning Characteristics of Building Materials, ASTM E84-13a. ASTM International, 2013.
Standard for Test for Surface Burning Characteristics of Building Materials, UL 723. Underwriter’s Laboratories, 2008.
Standard Specification for Loadbearing Concrete Masonry Units, ASTM C90-13. ASTM International, 2013.
Design for Dry Single-Wythe Concrete Masonry Walls, TEK 19 02B. Concrete Masonry & Hardscapes Association, 2012.
NFPA 285-[06] Approved Wall Assemblies Using Foam Plastic Insulation From Dow, Tech Solutions 514.0. Dow Chemical Company, 2009.
Building Code Requirements for Masonry Structures, TMS 402 11/ACI 530-11/ASCE 5-11. Reported by the Masonry Standards Joint Committee, 2011.
Standard Test Method for Determining Ignitability of Exterior Wall Assemblies Using a Radiant Heat Energy Source, NFPA 268. National Fire Protection Association, 2012.
Commercial Complete™ Wall System NFPA 285 Tested Wall Assemblies. Owens Corning Insulating Systems, LLC, 2012.

Concrete Masonry in the 2012 Edition of the IECC

November 2018

INTRODUCTION

Although masonry is an ancient material, today’s concrete masonry can be a significant benefit to modern sustainable buildings. In addition to its energy efficiency, concrete masonry is a locally produced natural material that is durable and long lived, minimizing the need for repair or replacement. Concrete masonry can incorporate recycled materials, and can itself be reused or recycled at the end of its life. Various architectural finishes are available that can eliminate the need for paint or other coatings which can impair indoor air quality or impede moisture control.

The International Energy Conservation Code (IECC) (ref. 1) serves as a written model for states, counties, cities or other jurisdictions to develop local codes for energy efficient building design. Concrete masonry construction can help meet these energy requirements, while also providing superior structural capacity, durability, and resistance to fire, sound transmission, insects and mold.

This TEK describes concrete masonry wall compliance for commercial buildings in accordance with the 2012 edition of the IECC.

CONCRETE MASONRY ENERGY PERFORMANCE

The thermal performance of a masonry wall depends on its steady state thermal characteristics (described by R-value and U-factor) as well as its thermal mass (described by heat capacity).

The steady-state and thermal mass performance are influenced by the size and type of masonry unit, cross-web configuration, type and location of insulation, finish materials, and density of masonry. Concrete masonry units (CMU) made with lower density concrete have higher R-values (i.e., lower U-factors) than units made with higher density concrete.

Thermal mass is the ability of materials such as concrete masonry to store heat—they heat up and cool down slowly, which can help mitigate heating and cooling loads. Due to the significant benefits of concrete masonry’s inherent thermal mass, concrete masonry buildings can often provide similar thermal performance to more heavily insulated frame buildings. The benefits of thermal mass have been incorporated into energy code requirements and computer models. The IECC and ANSI/ASHRAE/IESNA Standard 90.1, Energy Standard for Buildings Except Low-Rise Residential Buildings (ref. 2), permit concrete masonry walls to have less insulation than frame wall systems and metal buildings to meet the energy requirements

COMPLIANCE OPTIONS

For commercial buildings, there are three alternatives for demonstrating building energy compliance:

Prescriptive compliance, which requires each building envelope element to independently meet the R-value or U-factor requirements listed in IECC Table C402.1.2 or Table C402.2(1). The approach is simple to implement, but offers no design flexibility.
A building envelope trade-off procedure, which demonstrates that the envelope as a whole meets the energy requirements. This approach allows more design flexibility, since elements that do not meet prescriptive IECC requirements can be offset by other elements with higher performance. Although not specifically referenced in the code, COMcheck software (ref. 3) developed by the U. S. Department of Energy is a commonly accepted compliance tool for demonstrating total envelope performance.
A total building performance analysis, which simulates a full year of building operation. The analysis treats the entire building as a system, and accounts for virtually all aspects of building energy use, including the building envelope, mechanical systems, service water heating, and electric power and lighting. Detailed energy simulation software, such as EnergyPlus or eQuest (refs. 4, 5), is typically used when employing this option. This compliance path offers the maximum design flexibility, but requires a fairly rigorous and detailed analysis. For a project which will be LEED certified, a total building analysis is required, and the prescriptive criteria need not be met. See TEK 06-09C, Concrete Masonry and Hardscape Products in LEED 2009, (ref. 6) for more detailed information.

Note that a project need only comply under one of these compliance options, not all three. The following sections briefly describe prescriptive and trade-off compliance. See the design example at the end of the TEK for how these options may be implemented.

IECC PRESCRIPTIVE COMPLIANCE

Of the three compliance methods, the prescriptive method is easiest to apply. Requirements for building envelope components are listed in table format, by climate zone. Figure 1 illustrates the IECC climate zones.

Under the prescriptive option, requirements for individual elements are independent of each other. Hence, although using the prescriptive tables is very straightforward, it can also be very limiting in terms of design flexibility.

The IECC prescriptive building envelope requirements for commercial buildings (IECC section 402) list minimum energy performance criteria for roofs, above and below grade walls, slab-on-grade floors, and fenestration. The wall, roof and floor requirements are stated in terms of maximum assembly U-factor or minimum insulation R-value. The user may choose to use whichever table is more applicable to the project’s assemblies.

In the IECC prescriptive tables, concrete masonry walls fall under the Mass Wall category, which is defined as walls weighing at least 35 psf (171 kg/m2), or 25 psf (122 kg/m2) if the material weight is not more than 120 lb/ft3 (1,900 kg/m3).

Prescriptive Compliance via Overall Wall U-Factor

The 2012 IECC prescriptive U-factor requirements for above and below grade walls are shown in Table 1. U-factor is numerically the inverse of R-value. So, a wall with an overall R-value of 10 h. ft2.oF/Btu (1.76 m2.oK/W) has a U-factor of 0.10 Btu/h. ft2.oF (0.568 W/m2.oK) and vice-versa.

Using the U-factor criteria, rather than the insulation R-values discussed below, allows walls without continuous insulation (such as concrete masonry with insulated cores) to comply prescriptively. The U-factor compliance table may also be a good option for concrete masonry walls with proprietary inserts, or other walls that have better thermal performance than that assumed in the code.

CMHA TEK 06-02B, R-Values and U-Factors of Single Wythe Concrete Masonry Walls, and TEK 06-01C, R-Values of Multi-Wythe Concrete Masonry Walls, as well as the Thermal Catalog of Concrete Masonry Assemblies (refs. 7, 8, 9) list R-values, and in some cases U-factors, for a wide variety of concrete masonry walls.

Prescriptive Compliance via Insulation R-Value

Table 2 shows minimum insulation R-value requirements for above grade walls. These R-values apply to the insulation only, regardless of the underlying wall’s R-value.

In the table “ci” means continuous insulation. There is a widespread misconception that all walls must have continuous insulation in order to meet the IECC. In fact, continuous insulation is required only to comply with this particular table – other compliance options are available, including compliance via the prescriptive U-factor table discussed above, and COMcheck, discussed below.

Note that in Climate Zones 1 and 2, the IECC includes an exception for single wythe concrete masonry walls with insulated cores. Where the table requires R5.7 continuous insulation, the IECC allows concrete masonry walls with ungrouted cells filled with insulation such as vermiculite, perlite or foamed-in-place (with a thermal conductivity less than or equal to 0.44 Btu-in./h. ft2.oF, or R-value per inch > 2.27 (63.4 W.mm/m2.oK)) to comply, as long as the amount of grouting does not exceed 32 in. (813 mm) o.c. vertically and 48 in. (1,219 mm) o.c. horizontally. The exception allows the majority of single wythe ungrouted and partially grouted concrete masonry walls containing insulation in the ungrouted cells to comply with the IECC, regardless of that wall’s R-value.

TRADE-OFF COMPLIANCE USING COMCHECK

The trade-off option allows the user to demonstrate compliance based on the building envelope as a whole, rather than on the prescriptive component-by-component basis. These trade-offs are most often implemented using easy-to-use software, such as COMcheck (ref. 3).

There are two main benefits to using trade-off software for compliance rather than prescriptive tables. First, the user gains design flexibility because parameters such as increased glazing area can be offset by increasing roof or wall insulation. Second, once the basic building data is entered into the program and saved, design changes or building location can be quickly modified, and compliance immediately redetermined.

More detailed information on using COMcheck for concrete masonry buildings can be found in TEK 06-04B, Energy Code Compliance Using COMcheck (ref. 10).

DESIGN EXAMPLE

Consider a “big-box” retail building in St. Louis, MO (Climate Zone 4). For aesthetics and durability, the designer opts for single wythe core insulated 12-in. (305-mm) concrete masonry walls with an overall wall R-value of 6.3 Btu/h. ft2.oF (1.11m2.oK/W).

The first step is to check if the walls comply using one of the prescriptive compliance options, since they are the easiest to implement. Table 1 shows an above grade mass wall requirement of U0.104 h.ft2.oF/Btu (0.59 W/ m2.oK), which corresponds to a wall R-value of 9.6 Btu/h.ft2.oF (1.69 m2.oK/W). The R6.3 wall does not meet this requirement, nor can Table 2 be used because core insulation does not qualify as continuous insulation.

Using COMcheck, however the building can easily comply, by using the prescriptive minimum level of roof insulation (R25). Note that at the time of publication, because COMcheck did not yet include compliance via the 2012 IECC, compliance was demonstrated using ASHRAE 90.1-2010, which the IECC accepts as an alternate. See TEK 06-04B for more information on compliance using COMcheck.

BUILDING ENVELOPE AIR LEAKAGE REQUIREMENTS

The 2012 IECC includes substantially new air leakage criteria, requiring a continuous air barrier throughout the building envelope. The code also includes several “deemed-to-comply” materials and assemblies which are considered to comply with the code, including fully grouted concrete masonry, various surface coatings, and certain board insulations when installed with taped or sealed joints. The criteria, as well as a full discussion of how the criteria apply to concrete masonry assemblies can be found in TEK 06-14A, Control of Air Leakage in Concrete Masonry Walls, (ref. 11) Figures 2 and 3 in particular.

Concrete Masonry Basement Wall Construction

November 2018

Introduction

Basements allow a building owner to significantly increase usable living, working, or storage space at a relatively low cost. Old perceptions of basements have proven outdated by stateofthe-art waterproofing, improved drainage systems, and natural lighting features such as window wells. Other potential benefits of basements include room for expansion of usable space, increased resale value, and safe haven during storms.

Historically, plain (unreinforced) concrete masonry walls have been used to effectively resist soil loads. Currently, however, reinforced walls are becoming more popular as a way to use thinner walls to resist large backfill pressures. Regardless of whether the wall is plain or reinforced, successful performance of a basement wall relies on quality construction in accordance with the structural design and the project specifications.

Materials

Concrete Masonry Units: Concrete masonry units should comply with Standard Specification for Loadbearing Concrete Masonry Units, ASTM C 90 (ref. 8). Specific colors and textures may be specified to provide a finished interior to the basement. Drywall can also be installed on furring strips, if desired. A rule of thumb for estimating the number of concrete masonry units to order is 113 units for every 100 ft2 (9.3 m2) of wall area. This estimate assumes the use of 3/8 in. (9.5 mm) mortar joints.

Mortar: Mortar serves several important functions in a concrete masonry wall; it bonds the units together, seals joints against air and moisture penetration, and bonds to joint reinforcement, ties, and anchors so that all components perform as a structural element.

Mortar should comply with Standard Specification for Mortar for Unit Masonry, ASTM C 270 (ref. 9). In addition, most building codes require the use of Type M or S mortar for construction of basement walls (refs. 2, 4, 5, 9, 13), because Type M and S mortars provide higher compressive strengths. Table 1 lists mortar proportions.

Typical concrete masonry construction uses about 8.5 ft3 (0.24 m3) of mortar for every 100 ft2 (9.3 m2) of masonry wall area. This figure assumes 3/8 in. (9.5 mm) thick mortar joints, face shell mortar bedding, and a 10% allowance for waste.

Grout: In reinforced concrete masonry construction, grout is used to bond the reinforcement and the masonry together. Grout should conform to Standard Specification for Grout for Masonry, ASTM C 476 (ref. 10), with the proportions listed in Table 2. As an alternative to complying with the proportion requirements in Table 2, grout can be specified to have a minimum compressive strength of 2000 psi (13.8 MPa) at 28 days. Enough water should be added to the grout so that it will have a slump of 8 to 11 in. (203 to 279 mm). The high slump allows the grout to be fluid enough to flow around reinforcing bars and into small voids. This initially high water-to-cement ratio is reduced significantly as the masonry units absorb excess mix water. Thus, grout gains high strengths despite the initially high waterto-cement ratio.

Construction

Prior to laying the first course of masonry, the top of the footing must be cleaned of mud, dirt, ice or other materials which reduce the bond between the mortar and the footing. This can usually be accomplished using brushes or brooms, although excessive oil or dirt may require sand blasting.

Masons typically lay the corners of a basement first so that alignment is easily maintained. This also allows the mason to plan where cuts are necessary for window openings or to fit the building’s plan.

To make up for surface irregularities in the footing, the first course of masonry is set on a mortar bed joint which can range from 1/4 to 3/4 in. (6.4 to 19 mm) in thickness. This initial bed joint should fully bed the first course of masonry units, although mortar should not excessively protrude into cells that will be grouted.

All other mortar joints should be approximately 3/8 in. (9.5 mm) thick and, except for partially grouted masonry, need only provide face shell bedding for the masonry units. In partially grouted construction, webs adjacent to the grouted cells are mortared to restrict grout from flowing into ungrouted cores. Head joints must be filled solidly for a thickness equal to a face shell thickness of the units.

Tooled concave joints provide the greatest resistance to water penetration. On the exterior face of the wall, mortar joints may be cut flush if parging coats are to be applied.

When joint reinforcement is used, it should be placed directly on the block with mortar placed over the reinforcement in the usual method. A mortar cover of at least 5/8 in. (15.9 mm) should be provided between the exterior face of the wall and the joint reinforcement. A mortar cover of 1/2 in. (12.7 mm) is needed on the interior face of the wall. For added safety against corrosion, hot dipped galvanized joint reinforcement is recommended.

See Figures 1-4 for construction details.

Reinforced Masonry: For reinforced masonry construction, the reinforcing bars must be properly located to be fully functional. In most cases, vertical bars are positioned towards the interior face of basement walls to provide the greatest resistance to soil pressures. Bar positioners at the top and bottom of the wall prevent the bars from moving out of position during grouting. A space of at least 1/2 in. (12.7 mm) for coarse grout and 1/4 in. (6.4 mm) for fine grout should be maintained between the bar and the face shell of the block so that grout can flow completely around the reinforcing bars.

As mix water is absorbed by the units, voids can form in the grout. Accordingly, grout must be puddled or consolidated after placement to eliminate these voids and to increase the bond between the grout and the masonry units. Most codes permit puddling of grout when it is placed in lifts less than about 12 in. (305 mm). Lifts over 12 inches (305 mm) should be mechanically consolidated and then reconsolidated after about 3 to 10 minutes.

Surface Bonding: Another method of constructing concrete masonry walls is to dry stack units (without mortar) and then apply surface bonding mortar to both faces of the wall. The surface bonding mortar contains thousands of small glass fibers. When the mortar is applied properly to the required thickness, these fibers, along with the strength of the mortar itself, help produce walls of comparable strength to conventionally laid plain masonry walls. Surface bonded walls offer the benefits of excellent dampproof coatings on each face of the wall and ease of construction.

Dry-stacked walls should be laid in an initial full mortar bed to level the first course. Level coursing is maintained by using a rubbing stone to smooth small protrusions on the block surfaces and by inserting shims every two to four courses.

Water Penetration Resistance: Protecting below grade walls from water entry involves installation of a barrier to water and water vapor. An impervious barrier on the exterior wall surface can prevent moisture entry.

The barrier is part of a comprehensive system to prevent water penetration, which includes proper wall construction and the installation of drains, gutters, and proper grading.

Building codes (refs. 2, 4 , 5, 9, 13) typically require that basement walls be dampproofed for conditions where hydrostatic pressure will not occur, and waterproofed where hydrostatic pressures may exist. Dampproofing is appropriate where groundwater drainage is good, for example where granular backfill and a subsoil drainage system are present. Hydrostatic pressure may exist due to a high water table, or due to poorly draining backfill, such as heavy clay soils. Materials used for waterproofing are generally elastic, allowing them to span small cracks and accommodate minor movements.

When choosing a waterproof or dampproof system, consideration should be given to the degree of resistance to hydrostatic head of water, absorption characteristics, elasticity, stability in moist soil, resistance to mildew and algae, impact or puncture resistance, and abrasion resistance. A complete discussion of waterproofing, dampproofing, and drainage systems is included in TEK 19-03A (ref. 6).

All dampproofing and waterproofing systems should be applied to walls that are clean and free from dirt, mud and other materials which may reduce bond between the coating and the concrete masonry wall.

Draining water away from basement walls significantly reduces the pressure the walls must resist and reduces the possibility of water infiltration into the basement if the waterproofing (or dampproofing) system fails. Perforated pipe has historically proven satisfactory when properly installed. When placed on the exterior side of basement walls, perforated pipes are usually laid in crushed stone to facilitate drainage. To prevent migration of fine soil into the drains, filter fabrics are often placed over the gravel.

Drainage pipes can also be placed beneath the slab and connected into a sump. Pipes through the footing or the wall drain water from the exterior side of the basement wall.

The drainage and waterproofing systems should always be inspected prior to backfilling to ensure they are adequately placed. Any questionable workmanship or materials should be repaired at this stage since repairs are difficult and expensive after backfilling.

Backfilling: One of the most crucial aspects of basement construction is how and when to properly backfill. Walls should be properly braced or have the first floor in place prior to backfilling. Otherwise, a wall which is designed to be supported at the top may crack or even fail from the large soil pressures. Figure 5 shows one bracing scheme which has been widely used for residential basement walls. More substantial bracing may be required for high walls or large backfill pressures.

The backfill material should be free-draining soil without large stones, construction debris, organic materials, and frozen earth. Saturated soils, especially saturated clays, should generally not be used as backfill materials since wet materials significantly increase the hydrostatic pressure on the walls.

Backfill materials should be placed in several lifts and each layer should be compacted with small mechanical tampers. Care should be taken when placing the backfill materials to avoid damaging the drainage, waterproofing or exterior insulation systems. Sliding boulders and soil down steep slopes should thus be avoided since the high impact loads generated can damage not only the drainage and waterproofing systems but the wall as well. Likewise, heavy equipment should not be operated within about 3 feet (0.9 m) of any basement wall system.

The top 4 to 8 in. (102 to 203 mm) of backfill materials should be low permeability soil so rain water is absorbed into the backfill slowly. Grade should be sloped away from the basement at least 6 in. (152 mm) within 10 feet (3.1 m) of the building. If the ground naturally slopes toward the building, a shallow swale can be installed to redirect runoff.

Construction Tolerances

Specifications for Masonry Structures (ref. 8) specifies tolerances for concrete masonry construction. These tolerances were developed to avoid structurally impairing a wall because of improper placement.

Dimension of elements in cross section or elevation
…………………………………….¼ in. (6.4 mm), +½ in. (12.7 mm)
Mortar joint thickness: bed………………………..+⅛ in. (3.2 mm)
head………………………………..-¼ in (6.4 mm), +⅜ in. (9.5 mm)
Elements
- Variation from level: bed joints……………………………………….
  ±¼ in. (6.4 mm) in 10 ft (3.1 m), ±½ in. (12.7 mm) max
  top surface of bearing walls……………………………………………..
  ±¼ in.(6.4 mm), +⅜ in.(9.5 mm), ±½ in.(12.7mm) max
- Variation from plumb………….±¼ in. (6.4 mm) 10 ft (3.1 m)
  ………………………………………±⅜ in. (9.5 mm) in 20 ft (6.1 m)
  ……………………………………………±½ in. (12.7 mm) maximum
- True to a line…………………..±¼ in. (6.4 mm) in 10 ft (3.1 m)
  ………………………………………±⅜ in. (9.5 mm) in 20 ft (6.1 m)
  ……………………………………………±½ in. (12.7 mm) maximum
- Alignment of columns and bearing walls (bottom versus top)
  ……………………………………………………………..±½ in (12.7 mm)
Location of elements
- Indicated in plan……………..±½ in (12.7 mm) in 20 ft (6.1 m)
  …………………………………………….±¾ in. (19.1 mm) maximum
- Indicated in elevation
  ……………………………………….±¼ in. (6.4 mm) in story height
  …………………………………………….±¾ in. (19.1 mm) maximum

Insulation: The thermal performance of a masonry wall depends on its R-value as well as the thermal mass of the wall. Rvalue describes the ability to resist heat flow; higher R-values give better insulating performance. The R-value is determined by the size and type of masonry unit, type and amount of insulation, and finish materials. Depending on the particular site conditions and owner’s preference, insulation may be placed on the outside of block walls, in the cores of hollow units, or on the interior of the walls.

Thermal mass describes the ability of materials like concrete masonry to store heat. Masonry walls remain warm or cool long after the heat or air-conditioning has shut off, keeping the interior comfortable. Thermal mass is most effective when insulation is placed on the exterior or in the cores of the block, where the masonry is in direct contact with the interior conditioned air.

Exterior insulated masonry walls typically use rigid board insulation adhered to the soil side of the wall. The insulation requires a protective finish where it is exposed above grade to maintain durability, integrity, and effectiveness.

Concrete masonry cores may be insulated with molded polystyrene inserts, expanded perlite or vermiculite granular fills, or foamed-in-place insulation. Inserts may be placed in the cores of conventional masonry units, or they may be used in block specifically designed to provide higher R-values.

Interior insulation typically consists of insulation installed between furring strips, finished with gypsum wall board or panelling. The insulation may be fibrous batt, rigid board, or fibrous blown-in insulation.

Design Features

Interior Finishes: Split faced, scored, burnished, and fluted block give owners and designers added options to standard block surfaces. Colored units can be used in the entire wall or in sections to achieve specific patterns.

Although construction with staggered vertical mortar joints (running bond) is standard for basement construction, the appearance of continuous vertical mortar joints (stacked bond pattern) can be achieved by using of scored units or reinforced masonry construction.

Natural Lighting: Because of the modular nature of concrete masonry, windows and window wells of a variety of shapes and sizes can be easily accommodated, giving basements warm, natural lighting. For additional protection and privacy, glass blocks can be incorporated in lieu of traditional glass windows.

References

Basement Manual-Design and Construction Using Concrete Masonry, CMU-MAN-002-01, Concrete Masonry & Hardscapes Association, 2001.
BOCA National Building Code. Country Club Hills, IL: Building Officials and Code Administrators International, Inc. (BOCA), 1999.
Building Code Requirements for Masonry Structures, ACI 530-02/ASCE 5-02/TMS 402-02. Reported by the Masonry Standards Joint Committee, 2002.
International Residential Code. Falls Church, VA: International Code Council, 2000.
International Building Code. Falls Church, VA: International Code Council, 2000.
Preventing Water Penetration in Below-Grade Concrete Masonry Walls, TEK 19-03A. Concrete Masonry & Hardscapes Association, 2001.
Seismic Design Provisions for Masonry Structures, TEK 14-18B, Concrete Masonry & Hardscapes Association, 2009.
Specifications for Masonry Structures, ACI 530.1-02/ASCE 6-99/TMS 602-02. Reported by the Masonry Standards Joint Committee, 2002.
Standard Building Code. Birmingham, AL: Southern Building Code Congress International, Inc. (SBCCI), 1999.
Standard Specification for Grout for Masonry, ASTM C 476-01. American Society for Testing and Materials, 2001.
Standard Specification for Load-Bearing Concrete Masonry Units, ASTM C 90-01. American Society for Testing and Materials, 2001.
Standard Specification for Mortar for Unit Masonry, ASTM C 270-00. American Society for Testing and Materials, 2000.
Uniform Building Code. Whittier, CA: International Conference of Building Officials (ICBO), 1997.

Insulating Conrete Masonry Walls

August 2018

INTRODUCTION

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.
Grouting Concrete Masonry Walls, TEK 03-02A, Concrete Masonry & Hardscapes Association, 2005.

Earth-Sheltered Buildings

August 2018

INTRODUCTION

Earth-sheltering refers to using earth as part of a building’s thermal control system Earth-sheltered buildings can be either built into the earth or an existing hillside, or can be built above grade, and earth bermed around the exterior after construction. Earth-sheltered buildings can be built entirely underground, but are more often only partially earth-sheltered to allow adequate natural light into the interior. These buildings are most widely recognized for their energy efficiency, due to the insulating capacity of the earth and lower air infiltration through the earth-sheltered surfaces. In addition, earth sheltered buildings also offer superior protection from storms, insulation from outside noise, lower maintenance costs, and less impact on the surrounding landscape.

Concrete masonry is often the material of choice for earth-sheltered buildings. In addition to strength, durability, low maintenance and resistance to fire, soil gas, termites and other pests, the wide range of concrete masonry colors and textures provides an unlimited palette for the interior. Earth-sheltered buildings can also be constructed of conventional gray units, and easily finished with furring strips and drywall, since masonry is constructed square and plumb.

Earth-sheltered buildings are typically designed with passive solar features to further reduce mechanical heating and cooling requirements. In these designs, the concrete masonry absorbs solar energy, preventing interior overheating and providing heat after the sun sets. Types of passive solar systems and design considerations are covered in more detail in Passive Solar Design, TEK 06-05A (ref.1).

Many design and construction considerations for earth-sheltered buildings are the same as those for basements. For this reason, the reader is referred to Basement Manual: Design and Construction Using Concrete Masonry (ref. 2), which includes detailed information on structural design, water penetration resistance, crack control, insect protection, soil gas resistance as well as construction recommendations.

ENERGY EFFICIENCY

Earth-sheltered buildings save energy in several ways when compared to conventional structures. First, earth-sheltered buildings have a lower infiltration, or air leakage, rate. In homes, up to 20% of the total heating requirement can be due to infiltration. Almost half of that figure results from air leakage through walls other than windows or door openings. The earth covering effectively eliminates these losses.

Earth-sheltered construction also saves energy by reducing conduction heat losses through the walls and roof. The temperature difference between the building and the adjacent ground is typically much less than between an above grade structure and the outside air. In other words, the earth moderates the outdoor temperature swings, so that the earth-sheltered building is not subjected to as harsh an environment. In hot climates, the earth acts an a heat sink, helping keep the interior cooler.

CLIMATE AND SITE CONSIDERATIONS

Local climate can effect the practicality of earth-sheltering. Studies have shown that earth-sheltered houses are more cost effective in climates with larger daily temperature swings and low humidity, such as the northern Great Plains and the Rocky Mountains (ref. 3). In these locations, the earth temperature tends to be more stable than air temperatures, which allows the earth to act as a heat sink in hot weather and to insulate the building during cold weather.

Climate should also be considered when deciding on the type of earth-sheltered structure to build.

The site should be evaluated for water drainage. Choosing a site where the water will naturally drain away from the building is ideal. The finished grade should slope away from the building at least 6 in. in 10 ft (152 mm in 3.05 m) to carry surface water away. Where the topography is such that water flows towards the building, a shallow swale or trench can be constructed to intercept the water and divert it away from the structure.

In addition to the effect on water runoff, the site’s slope can significantly impact construction and design. Steeply sloping sites require much less excavation than flat or slightly sloping sites. South facing slopes work well in climates with a longer heating season, because the building can be easily designed with south-facing windows for direct solar gain (see also ref. 1). In climates with milder winters and hot summers, a north-facing slope may be preferable.

BUILDING MATERIALS

The choice of construction materials should consider the type of structure, depth below grade and soil type. Deeply buried buildings require stronger, more durable construction materials. The following is a brief list of recommendations for below-grade concrete masonry construction. Basement Manual: Design and Construction Using Concrete Masonry (ref. 2) contains more detailed recommendations as well as minimum requirements.

Concrete masonry units should be 8-in. (203-mm) or larger, depending on structural requirements. Use of unit shapes such as “A” or “H” facilitates unit placement around vertical reinforcing bars.
Type S mortar is generally recommended.
Joint reinforcement or horizontal reinforcing bars may be required to reduce potential shrinkage cracking and meet certain code requirements.
Grout, if used, must have a minimum compressive strength of 2,000 psi (13.8 MPa).
The concrete slab is typically a minimum of 2,500 psi (17.2 MPa) and 4 in. (102 mm) thick to allow the slab to span over weak soil areas without excessive cracking. Follow industry recommendations for subslab aggregate base and vapor barrier.
Backfill should preferably be free-draining material and should only be placed after the wall has gained sufficient strength and has been properly braced or supported.

TYPES OF EARTH-SHELTERED BUILDINGS

Earth-sheltered buildings can be constructed completely below grade or with part of the building above grade. An earth-sheltered building constructed completely below grade is referred to as an underground structure. More typically, though, the building is built partially or fully above grade, then earth is bermed up around one or more exterior walls. These bermed structures can in general accommodate more conventional building plans.

Underground Structures

Underground structures are most often designed using an atrium or courtyard design. This floorplan uses a subgrade central open area as the entry and focal point, and achieves an open feeling because it has four walls exposed to daylight. The structure is built completely below grade, typically on a flat site, and the interior spaces are arranged around a central outdoor courtyard. Windows and glass doors opening into the courtyard supply light, solar heat, natural ventilation, views and access to the ground level. Atrium/courtyard buildings are typically covered with less than 3 ft (0.91 m) of earth. Greater depths do not significantly improve the energy efficiency.

The atrium design provides minimal interruption to the natural landscape, good protection from winter winds and exterior noise, and a private outdoor space. Design considerations specific to atrium/courtyard structures are courtyard drainage and snow removal, as well as possibly limited passive solar gains, depending on the courtyard size and depth below grade.

Bermed Structures

Two general types of bermed structures are elevational and penetrational. Elevational floorplans have one whole building face exposed, while the other sides, and sometimes the roof, are covered with earth. The covered sides protect and insulate, while the exposed face, typically facing south, provides views, natural light and solar heat. This type of structure is typically set into the side of a hill, and tends to be the easiest type of earth sheltered building to construct, and therefore the most economical. Skylights and/or additional ventilation may need to be considered for the north-facing interior spaces.

Penetrational designs are built above grade, with earth bermed around and on top of it. The entire building is covered, except at windows and doors, where the earth is retained. This design allows natural light from all walls of the building, as well as cross-ventilation.

INSULATION PLACEMENT

Not all experts agree on the amount of insulation required nor the optimum placement around the structure, but two points are generally well agreed on:

(1) It is generally not cost-effective to insulate below the floor slab in an earth-sheltered building. Edge insulation is a good investment on walls that are not bermed.

(2) Insulation should be placed on the exterior side of the walls. Exterior insulation protects the waterproofing from abrasion damage and allows the thermal mass of the below-grade concrete masonry walls to contribute to the energy savings and indoor temperature moderation.

Because of the insulating effect of the soil, insulation is more effective for buildings located closer to the surface of the ground. Normally, for earth cover less than 5 ft (1.52 m) over the ceiling, the ceiling should be insulated. In most cases, it is less expensive to insulate the ceiling than to increase the roof capacity to carry the load of the additional earth.

Figure 1 shows four variations of insulation placement, with some general performance guidelines for underground buildings. Note that in some cases, insulation which is effective at reducing winter heat losses can actually be detrimental when cooling needs are considered. For this reason, it is important to match the insulation strategy to the heating and cooling needs of the building.

WATER PENETRATION RESISTANCE

All below-grade spaces are potentially vulnerable to water penetration from rainfall, melting snow, irrigation and natural groundwater, regardless of the construction materials used. For adequate protection, the following should be employed (see ref. 2 for a complete discussion):

Identify the water sources (precipitation, irrigation, groundwater and/or condensation) and address potential water entry points prior to construction.
Follow proper construction techniques and details
Provide drainage to direct surface and roof water away from the structure.
Install a subsurface drainage system to collect and direct water away from the foundation.
Apply damp-proofing or waterproofing systems to the masonry walls. A drainage board can also be used to drain water quickly and reduce backfill pressure.

OTHER CONSIDERATIONS

Earth-sheltered buildings require all of the considerations typically associated with basement design and construction, such as structural capacity, insect protection and soil gas protection. In addition, considerations such as adequate ventilation, egress and natural light may also be considerations for earth-sheltered structures.

Adequate ventilation must be carefully planned for earth sheltered buildings. Ventilation is the exchange of indoor air for outdoor air, and reduces indoor pollutants, odors and moisture. For buildings with low air leakage, such as earth-sheltered buildings, natural ventilation alone should not be relied upon. Instead, the building should utilize a mechanical ventilation system. ASHRAE recommends balanced air to-air systems with heat recovery for very air-tight homes (ref. 6).

The International Residential Code (IRC) (ref. 7) requires all habitable rooms to have a minimum glazing area of 8% of the room’s floor area, with minimum openable area of 4% of the floor area to provide natural ventilation. For earth-sheltered homes, if these requirements cannot be met using windows, doors, window wells and skylights, the IRC includes exceptions for homes with mechanical ventilation capable of providing 0.35 air changes per hour in the room or a whole-house system capable of supplying 15 ft3 /min. (7.08 L/s) of outdoor air per occupant. Supplementary artificial lighting may also be required.

In addition, bedrooms are required to have at least one openable emergency escape and rescue opening with a minimum net clear opening of 5.7 ft2 (0.530 m2). Window wells must have a horizontal area at least 9 ft2 (0.84 m2), with a minimum projection and width of 36 in. (914 mm). These emergency egress requirements may drive the building layout. Homes designed using an “elevational” floorplan, for example, tend to be long and narrow, so that the bedrooms and main living spaces are aligned along the above-grade wall.

Indoor humidity can increase during the summer, which can lead to problems such as condensation and mold if not addressed. Exterior insulation on the walls prevents the walls from cooling down to the earth temperature, but also reduces the heat sink effect for summer cooling. Mechanical dehumidification or air conditioning may be required to control indoor humidity levels.

REFERENCES

Passive Solar Design, TEK 06-05A, Concrete Masonry & Hardscapes Association, 2006.
Basement Manual: Design and Construction Using Concrete Masonry, CMU-MAN-002-01, Concrete Masonry & Hardscapes Association, 2001.
EERE Consumers Guide: Site-Specific Factors for Earth Sheltered Home Design. U. S. Department of Energy, 2005.
Earth-Sheltered Home Design. U. S. Department of Energy, http://www.eere.energy.gov/consumer/your_home/designing_rem deling/index.cfm/mytopic=10100.
Forowicz, T. Z. An Anlaysis of Different Insulation Strategies for Earth-Sheltered Buildings. ASHRAE Transactions, Vol. 100 Part 2, 1994.
2005 ASHRAE Handbook Fundamentals. American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc., 2005.
2003 International Residential Code for One and Two Family Dwellings. International Code Council, 2003.

R-Values and U-Factors of Single Wythe Concrete Masonry Walls

August 2018

INTRODUCTION

Single wythe concrete masonry walls are often constructed of hollow units with cores filled with insulation and/or grout. This construction method allows insulation and reinforcement to be used to increase thermal and structural performance, respectively, without increasing the wall thickness.

U-factors and R-values are used to estimate heat flow under steady state conditions (neglecting the effects of thermal mass). These steady-state values can be used in conjunction with factors such as thermal mass, climate, and building orientation to estimate a building envelope’s thermal performance, typically using software.

This TEK lists thermal resistance (R) and thermal transmittance (U) values of single wythe walls. Cavity wall R-values are listed in TEK 06-01C, R-Values of Multi-Wythe Concrete Masonry Walls (ref. 1).

The R-values/U-factors listed in this TEK were determined by calculation using the code-recognized series-parallel (also called isothermal planes) calculation method (refs. 2, 3, 4). The method accounts for the thermal bridging (energy loss) that occurs through the webs of concrete masonry units. The method is fully described in TEK 06-01C. Alternate code approved means of determining R values of concrete masonry walls include two-dimensional calculations and testing (ref. 2).

CONCRETE MASONRY ENERGY PERFORMANCE

Although this TEK presents a compendium of concrete masonry assembly R-values and U-factors, it is important to note that R values/U-factors alone do not fully describe the thermal performance of a concrete masonry assembly.

Concrete masonry’s thermal performance depends on both its steady state thermal characteristics (described by R-value or U-factor) as well as its thermal mass (heat capacity) characteristics. The steady state and mass performance are influenced by the size, type, and configuration of masonry unit, type and location of insulation, finish materials, density of masonry, climate, and building orientation and exposure conditions.

Thermal mass describes the ability of materials to store energy. Because of its comparatively high density and specific heat, masonry provides very effective thermal storage. Masonry walls retain their temperature long after the heat or air-conditioning 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 energy performance to more heavily insulated light frame buildings.

These thermal mass effects have been incorporated into energy code requirements as well as sophisticated computer models. Due to the thermal mass, 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 Standard 90.1 (ref. 2), require less insulation in concrete masonry assemblies than equivalent light-frame systems. Although applicable to all climates, the greater benefits of thermal mass tend to be found in warmer climates (lower-numbered Climate Zones).

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 assemblies may require additional insulation, particularly when designed under more contemporary building code requirements or to achieve above-code thermal performance. For such conditions, there are many options available for insulating concrete masonry construction.

Although in general higher R-values reduce energy flow through a building element, R-values have a diminishing impact on the overall building envelope energy use. In other words, it’s important not to automatically equate higher R-value with improved energy efficiency. As an example, consider a two story elementary school in Bowling Green, Kentucky. If this school is built using single wythe concrete masonry walls with cell insulation only and a resulting wall R-value of 7 hr.ft2.oF/Btu (1.23 m2.K/W), an estimate of the building envelope energy use for this structure is approximately 27,800 Btu/ft2 (87.7 kW.h/m2), as shown in Figure 1. If we increase the R-value of the wall to R14 by adding additional insulation while holding the other envelope variables constant, the building envelope energy use drops by only 2.5%, which is not in proportion to doubling the wall R-value. Figure 1 illustrates this trend: as wall R-value increases, it has less and less impact on the building envelope thermal performance.

In this example, a wall R-value larger than about R12 no longer has a significant impact on the envelope energy use. At this point, it makes more sense to invest in energy efficiency measures other than wall insulation.

When required, concrete masonry can provide assemblies with R values that exceed code minimums. For overall project economy, however, the industry recommends balancing needs and performance expectations with reasonable insulation levels.

ENERGY CODE COMPLIANCE

Compliance with prescriptive energy code requirements can be demonstrated by:

the concrete masonry wall by itself or the concrete masonry wall plus a prescribed R-value of added insulation, or
the overall U-factor of the wall.

The IECC prescriptive R-value table 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 of continuous insulation include rigid insulation adhered to the interior of the wall with furring and drywall applied over the insulation, continuous insulation in the cavity of a masonry cavity wall, and exterior insulation and finish systems. These and other insulation options for concrete masonry assemblies are discussed in TEK 06 11A, Insulating Concrete Masonry Walls (ref. 6).

If the concrete masonry assembly will not include continuous insulation, there are several other options to comply with the IECC requirements—concrete masonry assemblies are not required to have continuous insulation in order to meet the IECC, regardless of climate zone.

Other compliance methods include: prescriptive U-factor tables, and computer programs which may require U-factors and heat capacity (a property used to indicate the amount of thermal mass) to be input for concrete masonry walls. See TEK 06-04B, Energy Code Compliance Using COMcheck, (ref. 7) for more detailed information. Another compliance method, the energy cost budget method, incorporates sophisticated modeling to estimate a building’s annual energy cost.

A more complete discussion of concrete masonry IECC compliance can be found in TEK 06-12E (for the 2012 IECC) (ref. 8).

CONCRETE MASONRY UNIT CONFIGURATIONS

Revisions in 2011 to ASTM C90¸ Standard Specification for Loadbearing Concrete Masonry Units (ref. 9) have significantly reduced the minimum amount of web material required for CMU. Values in this TEK are based on concrete masonry units with three webs, with each web being the full height of the unit, and having a minimum thickness as provided in historical versions of ASTM C90 (see Table 1).

The changes in C90, however, allow a much wider range of web configurations, with corresponding changes in R-values and U-factors (because the webs of a CMU act as thermal bridges, reducing the CMU web area increases the R-value of the corresponding concrete masonry assembly). More discussion on the impact of web configuration and thermal performance can be found in CMU-TEC 001-23, Concrete Masonry Unit Shapes, Sizes, Properties, and Specifications (ref. 10).

The Thermal Catalog of Concrete Masonry Assemblies (ref.11) lists R-values and U-factors of traditional units, as included here, as well as wall assemblies with smaller web areas, as now allowed by ASTM C90. The additional wall assemblies are based on:

CMU having two full-height 3/4 in. (19 mm) thick webs, and
a ‘hybrid’ system of CMU, intended to maximize thermal efficiency. The hybrid system uses the two-web units described above for areas requiring a grouted cell, and a one-web unit where grout confinement is not required.

Although the R-values/U-factors in Table 2 are based on typical 8-in. (203-mm) high concrete masonry units, 4-in. (102 mm) high units (commonly called “half-high” units) are also widely available, and other heights may be available in some markets. Because the wall R values vary so little with different unit heights, the values in Table 2 can be applied to units with heights other than 8 in. (203 mm).

U-FACTOR AND R-VALUE TABLES – TRADITIONAL THREE-WEB UNITS

Table 2 lists calculated U-factors and R-values of various thicknesses of concrete masonry walls, for concrete densities of 85 to 135 lb/ft3 (1,362 to 2,163 kg/m3), with various core fills. Table 3 shows the approximate percentage of grouted and ungrouted wall area for different vertical and horizontal grout spacings, which can be used to determine R-values of partially grouted walls (see following section).

In addition to the core insulations listed across the top of Table 2, polystyrene inserts are available which fit in the cores of concrete masonry units. Inserts are available in many shapes and sizes to provide a range of insulating values and accommodate various construction conditions. Specially designed concrete masonry units may incorporate reduced height webs to accommodate inserts. Such webs also reduce thermal bridging through masonry, since the reduced web area provides a smaller cross-sectional area for energy flow. To further reduce thermal bridging, some manufacturers have developed units with two webs rather than three. In addition, some inserts have building code approval to be left in the grouted cores, thus improving the thermal performance of fully or partially grouted masonry walls.

The values for insulated and grouted cores in Table 2 are based on the assumption that all masonry cores are insulated or grouted, respectively. In other words, for ungrouted walls and fully grouted, the values in Table 2 can be used directly. For partially grouted walls, refer to the following section.

R-values of various interior and exterior insulation and finish systems are listed in Table 4. (Note that the use of batt insulation is not recommended, due to its susceptibility moisture.) These R-values can be added to the wall R-values in Table 2. After adding the R-values, the wall U-factor can be found by inverting the total R-value (i.e., U = 1 /R) (see also the following example). Note that tables of precalculated R-values and U-factors, including the various insulation and finish systems, are available in Thermal Catalog of Concrete Masonry Assemblies.

Thermal properties used to compile the tables are listed in Table 5.

R-VALUES AND U-FACTORS OF PARTIALLY GROUTED CONCRETE MASONRY

For partially grouted walls, the values in Table 2 must be modified to account for the grouted cores, using an area weighted average approach. The first step is to determine how much of the wall area is grouted (see Table 3). The U-factor of the wall is calculated from the area-weighted average of the U-factors of the grouted area and ungrouted areas as follows:

For example, consider an 8 in. (203 mm) wall composed of hollow 105 lb/ft3 (1682 kg/m3) concrete masonry, and grouted at 48 in. (1,219 mm) o.c. both vertically and horizontally. The ungrouted cores contain polyurethane foamed-in-place insulation, and the wall is finished on the interior with gypsum wallboard.

REFERENCES

R-Values of Multi-Wythe Concrete Masonry Walls, TEK 06-01C, Concrete Masonry & Hardscapes Association, 2013.
Energy Standard for Buildings Except Low-Rise Residential
Buildings, ANSI/ASHRAE/IESNA 90.1-2010. American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc., 2010.
ASHRAE Handbook, Fundamentals. American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc., 2009.
Guide to Thermal Properties of Concrete and Masonry Systems. ACI 122R-02. American Concrete Institute, 2002.
International Energy Conservation Code. International Code Council, 2006, 2009, 2012.
Insulating Concrete Masonry Walls, TEK 06-11A, Concrete
Masonry & Hardscapes Association, 2010.
Energy Code Compliance Using COMcheck, TEK 06-04B, Concrete Masonry & Hardscapes Association, 2012.
Concrete Masonry in the 2012 Edition of the IECC, TEK 06-12E, Concrete Masonry & Hardscapes Association, 2012.
Standard Specification for Loadbearing Concrete Masonry Units, ASTM C90-11. ASTM International, 2011.
Concrete Masonry Unit Shapes, Sizes, Properties, and Specifications, CMU-TEC-001-23, Concrete Masonry & Hardscapes Association, 2023.
Thermal Catalog of Concrete Masonry Assemblies, Second Edition, CMU-MAN-004-12, Concrete Masonry & Hardscapes Association, 2012.

R-Values of Multi-Wythe Concrete Masonry Walls

August 2018

INTRODUCTION

Multi-wythe concrete masonry construction lends itself to placing insulation between two wythes of masonry when the wythes are separated to form a cavity. Placing insulation between two wythes of masonry offers maximum protection for the insulation while allowing a vast amount of the thermal mass to be exposed to the conditioned interior to help moderate temperatures. Masonry cavity walls can easily meet or exceed energy code requirements, because the cavity installation allows a continuous layer of insulation to envelop the masonry. When properly sealed, this continuous insulation layer can also increase energy efficiency by mitigating air infiltration/exfiltration.

Cavity wall construction provides hard, durable surfaces on both sides of the assembly, efficiently utilizing the inherent impact resistance and low maintenance needs of concrete masonry. While these needs are most commonly associated with multifamily dwellings, hospitals, schools and detention centers, the benefits of resistance to damage from hail, shopping and loading carts, gurneys, motorized chairs, and even sports make cavity construction ideal for any application.

This TEK lists thermal resistance (R) values of multi-wythe walls. Single wythe R-values are listed in TEK 06-02C, R-Values and U Factors of Single Wythe Concrete Masonry Walls (ref. 1).

The R-values listed in this TEK were determined by calculation using the code-recognized series-parallel (also called isothermal planes) calculation method (refs. 2, 3, 4). The method accounts for the thermal bridging (energy loss) that occurs through the webs of concrete masonry units. The method is fully described on page 4 of this TEK. Alternate code-approved means of determining R-values of concrete masonry walls include two dimensional calculations and testing (ref. 2).

CAVITY WALLS

The term cavity insulation, which in some codes refers to the insulation between studs in lightweight framing systems, should not be confused with the long established term “masonry cavity wall.” Cavity walls are comprised of at least two wythes of masonry separated by a continuous airspace (cavity).

Under current building code requirements a 1 in. (25-mm) clear airspace between the insulation and the outer wythe is required (2 in. (51 mm) is preferred) to help ensure free water drainage (ref. 5).

Cavity walls are typically designed and detailed using actual out-to out dimensions. Thus, a 14-in. (356-mm) cavity wall with a nominal 4 in. (102-mm) exterior wythe and 8-in. (203-mm) backup wythe has an actual cavity width of 23/4 in. (68 mm), allowing for 11 /2 in. (38 mm) of rigid board insulation.

Typical cavity walls are constructed with a 4, 6, 8, 10 or 12 in. (102, 152, 203, 254 or 305 mm) concrete masonry backup wythe, a 2 to 41 /2 in. (51 to 114 mm) wide cavity, and a 4-in. (102-mm) masonry veneer. By reference to Specification for Masonry Structures (ref. 6), the International Building Code (ref. 7) allows cavity widths up to 41/2 in. (114 mm), beyond which a detailed wall tie analysis must be performed. More detailed information on cavity walls can be found in References 8 through 11.

Changing the interior finish materials of a multi-wythe assembly does not typically change the overall assembly R-value significantly, unless the finish material itself is insulative. For cavity assemblies with interior-side finish materials installed on furring, such as wood paneling, the R-values for 1/2 in. (13 mm) gypsum wallboard on furring in Table 4 can be used as a very close approximation.

CONCRETE MASONRY ENERGY PERFORMANCE

Although this TEK presents concrete masonry assembly R-values, it is important to note that R-values or U-factors alone do not fully describe the thermal performance of a concrete masonry assembly.

Thermal mass describes the ability of materials to store energy. Because of its comparatively high density and specific heat, masonry provides very effective thermal storage. Masonry walls retain their temperature long after the heat or air-conditioning 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 energy performance to more heavily insulated light frame buildings.

These thermal mass effects have been incorporated into energy code requirements as well as sophisticated computer models. Due to the thermal mass, energy codes and standards such as the International Energy Conservation Code (IECC) (ref. 12) and Energy Efficient Standard for Buildings Except Low-Rise Residential Buildings, ASHRAE Standard 90.1 (ref. 2), require less insulation in concrete masonry assemblies than equivalent light-frame systems. Although applicable to all climates, the greater benefits of thermal mass tend to be found in warmer climates (lower-numbered Climate Zones).

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 assemblies may require additional insulation, particularly when designed under more contemporary building code requirements or to achieve above-code thermal performance. For such conditions, there are many options available for insulating concrete masonry construction.

Although in general higher R-values reduce energy flow through a building element, R-values have a diminishing impact on the overall building envelope energy use. In other words, it’s important not to automatically equate higher R-value with improved energy efficiency. As an example, consider a two-story elementary school in Bowling Green, Kentucky. If this school is built using single wythe concrete masonry walls with cell insulation only and a resulting wall R-value of 7 hr. ft2.oF/Btu (1.23 m2.K/W), an estimate of the building envelope energy use for this structure is approximately 27,800 Btu/ft2 (87.7 kW. h/m2), as shown in Figure 1. If we increase the R-value of the wall to R14 by adding additional insulation while holding the other envelope variables constant, the building envelope energy use drops by only 2.5%, which is not in proportion to doubling the wall R-value. Figure 1 illustrates this trend: as wall R-value increases, it has less and less impact on the building envelope thermal performance.

ENERGY CODE COMPLIANCE

Compliance with prescriptive energy code requirements can be demonstrated by:

the concrete masonry wall by itself or the concrete masonry wall plus a prescribed R-value of added insulation, or

the overall U-factor of the wall.

Other compliance methods include prescriptive U-factor tables and computer programs which may require U-factors and heat capacity (a property used to indicate the amount of thermal mass) to be input for concrete masonry walls. See TEK 06-04B, Energy Code Compliance Using COMcheck, (ref. 14) for more detailed information. Another compliance method, the energy cost budget method, incorporates sophisticated modeling to estimate a building’s annual energy cost. A more complete discussion of concrete masonry IECC compliance can be found in TEK 06-12E (for the 2012 IECC) (ref. 15).

CONCRETE MASONRY UNIT CONFIGURATIONS

Revisions in 2011 to ASTM C90¸ Standard Specification for Loadbearing Concrete Masonry Units (ref. 16) have significantly reduced the minimum amount of web material required for CMU. Values in this TEK are based on concrete masonry units with three webs, with each web being the full height of the unit, and having a minimum thickness as provided in historical versions of ASTM C90 (see Table 1).

The Thermal Catalog of Concrete Masonry Assemblies (ref.18) lists R-values and U-factors based on traditional units, as included here, as well as units with smaller web areas, as now allowed by ASTM C90. The additional wall assemblies are based on:

CMU having two full-height 3 /4 in. (19 mm) thick webs, and
a ‘hybrid’ system of CMU, intended to maximize thermal efficiency. The hybrid system uses the two-web units described above for areas requiring a grouted cell, and a one-web unit where grout confinement is not required.

R-VALUE TABLES-TRADITIONAL THREE-WEB UNITS

Table 2 presents R-values of uninsulated concrete masonry cavity walls with 4, 6, 8, 10 and 12 in. (102, 152, 203, 254 and 305 mm) backup wythes and a 4 in. (102 mm) hollow unit concrete masonry veneer. These R-values should be added to the applicable R-values in Tables 3 and 4 to account for cavity insulation and/or interior furring with insulation, respectively. Table 5 contains the thermal data used to develop the tables.

To convert the R-value to U-factor (as may be needed for code compliance), simply invert the R-value, i.e.: U = 1/R. Note that U factors of various wall components cannot be directly added together. To determine the overall cavity wall U-factor, first add the component R-values together, then determine overall U-factor by inverting the total R-value.

As an example, to determine the R-value of a concrete masonry cavity wall with 8 in. (152 mm) 105 pcf (1,682 kg/m3) backup insulated with 2 in. (51 mm) of extruded polystyrene insulation in the cavity, first determine the R-value of the uninsulated wall from Table 2 (4.22 ft2.hr.oF/Btu, 0.74 m2.K/W), then add the cavity insulation R value from Table 3 (10 ft2.hr.oF/Btu, 1.8 m2.K/W), to obtain the total R-value of 14.2 ft2.hr.oF/Btu (2.5 m2.K/W). The corresponding U factor for this wall is:

U = 1/R = 1/14.2 = 0.070 Btu/ hr.oF/Btu (0.4 W/ m2.K)

Note that tables of precalculated R-values and U-factors, including the various insulation and finish systems, are available in Thermal Catalog of Concrete Masonry Assemblies.

The values in Table 2 are based on an ungrouted backup wythe. However, the addition of grout to a hollow concrete masonry backup wythe does not significantly affect the overall R-value of an insulated cavity wall. For example, the R-value of a cavity wall with 8 in. (203 mm) ungrouted 105 pcf (1,682 kg/m3) backup and insulated cavity decreases only about 5% when the backup wythe is solidly grouted. With a partially-grouted backup, the difference in R-value is smaller than 5%.

Calculations are performed using the series-parallel (also called isothermal planes) calculation method (refs. 2, 3, 4). The method accounts for the thermal bridging that occurs through the webs of concrete masonry units. The method is briefly described below, and its use is demonstrated in Appendix C of Thermal Catalog of Concrete Masonry Assemblies.

REFERENCES

R-Values and U-Factors of Single Wythe Concrete Masonry Walls, TEK 06-02C, Concrete Masonry & Hardscapes Association, 2013.
Energy Standard for Buildings Except Low-Rise Residential
Buildings, ANSI/ASHRAE/IESNA 90.1-2010. American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc., 2010.
ASHRAE Handbook, Fundamentals. American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc., 2009.
Guide to Thermal Properties of Concrete and Masonry Systems. ACI 122R-02. American Concrete Institute, 2002.
Building Code Requirements for Masonry Structures, TMS 402/ACI 530/ASCE 5. Reported by the Masonry Standards Joint Committee, 2005, 2008, 2011.
Specification for Masonry Structures, TMS 602/ACI 530.1/ASCE 6. Reported by the Masonry Standards Joint Committee, 2005, 2008, 2011.
International Building Code. International Code Council, 2006, 2009, 2012.
Concrete Masonry Veneers, TEK 03-06C, Concrete Masonry & Hardscapes Association, 2012.
Concrete Masonry Veneer Details, TEK 05-01B, Concrete Masonry & Hardscapes Association, 2003.
Design of Concrete Masonry Noncomposite (Cavity) Walls, TEK 16-04A, Concrete Masonry & Hardscapes Association, 2004.
Flashing Details for Concrete Masonry Walls, TEK 19-05A,
Concrete Masonry & Hardscapes Association, 2008.
International Energy Conservation Code. International Code Council, 2006, 2009, 2012.
Insulating Concrete Masonry Walls, TEK 06-11A, Concrete
Masonry & Hardscapes Association, 2010.
Energy Code Compliance Using COMcheck, TEK 06-04B,
Concrete Masonry & Hardscapes Association, 2012.
Concrete Masonry in the 2012 Edition of the IECC, TEK 06-12E, Concrete Masonry & Hardscapes Association, 2012.
Standard Specification for Loadbearing Concrete Masonry Units, ASTM C90-11. ASTM International, 2011.
Concrete Masonry Unit Shapes, Sizes, Properties, and Specifications, CMU-TEC-001-23, Concrete Masonry &
Hardscapes Association, 2023.
Thermal Catalog of Concrete Masonry Assemblies, Second Edition, CMU-MAN-004-12, Concrete Masonry & Hardscapes Association, 2012.