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Noise Control With Concrete Masonry

  • August 2018

INTRODUCTION

Sound control is an important design consideration in most buildings. Sound control involves two important properties: sound transmission and sound absorption, as depicted in Figure 1. The International Building Code (IBC, refs. 1, 2) contains minimum requirements for sound transmission in certain situations (see Sound Transmission Class Ratings of Concrete Masonry Walls, TEK 13-01D, ref. 3). However, the IBC does not contain minimum requirements for sound absorption, although proper control of sound reflected back into the room is a very important design function in many buildings as well, such as concert halls, gymnasiums, places of assembly, rooms containing loud equipment.

Concrete masonry is an ideal noise control material for both properties: it can act as a barrier by diffusing incident noise over a wide range of frequencies; and it can be an effective sound absorption material for absorbing noise generated within a room. This TEK discusses the sound absorption and sound transmission properties of concrete masonry, and provides general design guidance to help provide a good acoustic environment.

Figure 1—Sound Attenuation Characteristics of Concrete Masonry

MAXIMIZING SOUND ABSORPTION

Sound absorption control involves minimizing sound reflection, so that the noise generated within the space is not echoed back into the space. Sound absorption is most important in applications like assembly areas or concert halls. The extent of control provided by a particular surface depends on that surface’s ability to absorb rather than reflect sound waves. This ability is estimated by the surface’s sound absorption coefficient: an indication of its sound absorbing efficiency. A surface which can theoretically absorb 100% of incident sound would have a sound absorption coefficient of 1. Similarly, a surface capable of absorbing 45% of incident sound has a sound absorption coefficient of 0.45.

Because the sound absorption coefficient typically varies with the frequency of the incident sound, the sound absorption coefficients measured at various frequencies are averaged together to produce an overall absorption coefficient. Standard Test Method for Sound Absorption and Sound Absorption Coefficients by the Reverberation Room Method, ASTM C423 (ref. 4) prescribes the test method and calculations. Traditionally, sound absorption has been reported in terms of the noise reduction coefficient (NRC), determined by taking a mathematical average of the sound absorption coefficients obtained at frequencies of 250, 500, 1,000 and 2,000 Hertz. More recently, the Sound Absorption Average (SAA) has been added to ASTM C423. Although the SAA is very similar to NRC, it is determined by averaging the sound absorption coefficients obtained at the twelve one-third octave bands from 200 through 2,500 Hz. ASTM C423 requires that both NRC and SAA be reported. Experience in the concrete masonry industry has shown that the new SAA values and the old NRC values vary little and generally are within 1 or 2 percentage points of each other.

Sound absorption values depend primarily on the surface texture and porosity of the material under consideration. More porous and open-textured surfaces are able to absorb more sound and, hence, have a higher value. This is reflected in the concrete masonry NRC values listed in Table 1. Note that painting a concrete masonry wall closes small surface openings, and hence decreases the wall’s sound absorption value.

Table 1—Approximate Noise Reduction Coefficients

MINIMIZING SOUND TRANSMISSION

Sound insulation, as between dwelling units, is accomplished by designing walls to minimize sound transmission. For this purpose, effectiveness primarily depends on wall weight, rather than on surface texture. In general, the heavier a concrete masonry wall is, the more effectively it will block sound transmission.

The sound transmission class (STC) rating provides an indication of how effectively a given wall prevents sound transmission across a range of frequencies. STC ratings for concrete masonry walls are determined using Standard Method for Determining the Sound Transmission Class Rating for Masonry Walls, TMS 0302 (ref. 5). TEK 13-01D, Sound Transmission Class Ratings of Concrete Masonry Walls, contains a complete discussion on determining STC ratings, applicable building code requirements, as well as tabulated values for various concrete masonry walls.

WALL SELECTION

When used for noise control, concrete masonry walls should be evaluated for both surface texture and density. Sound transmission is reduced by using heavier walls, but may be increased by using units with a very open surface texture. Transmission loss characteristics of unpainted, open-textured units can be increased by plastering or painting, although this will also result in a corresponding reduction in the sound absorption (SAA or NRC) of the block.

In some cases, the designer may wish to use both the transmission loss and absorption properties of concrete masonry to advantage. For example, using open textured units in a cavity wall with back plastering on the inside face of one or both wythes provides sound absorption on both sides of the wall as well as sound transmission reduction. Another option for providing both effective sound absorption and sound transmission loss is the use of acoustical concrete masonry units, such as those shown in Figure 2. These units typically have an opening molded into the face shell, to allow sound energy to readily enter the masonry cells. The cells are designed to incorporate systems such as metal septa and/or fibrous fillers to dissipate the sound energy and minimize sound transmission.

Figure 2—Examples of Acoustical Concrete Masonry Units (viewed from bottom)

DESIGN AND CONSTRUCTION

Early in the design, a detailed noise survey should be conducted to determine the outside noise level and the anticipated background noise level in the various building areas. A building layout can then be developed which will help reduce noise transmission from one area to another. Effective sound control depends on proper layout and wall selection as well as good construction techniques.

Sound will be easily transmitted through any opening in a wall. An improperly fitted corridor door is a prime source of sound leakage, as well as openings around ducts, piping and electrical outlets which are improperly fitted or sealed. A crack just 0.007 in. (0.178 mm) wide along the top of a 12½ ft (3.8 m) wall will allow as much transmitted sound as a 1 in.² (645 mm²) hole. Hence, it is very important to seal all cracks, joints and gaps to maintain the acoustical integrity of the wall.

Building design and layout can also impact the building’s acoustic effectiveness. Planning early in the design process can help alleviate potential problem areas farther down the line. For example, individual spaces should be planned to minimize common walls whenever possible (see Figure 3), and to place adjacent spaced such that quieter areas (such as bedrooms) abut each other, and noisy areas (such as kitchens) abut similar noisy areas (see Figure 4).

When considering building layout, also note that sound travels most effectively in straight lines. Every time sound energy changes direction, some of it is absorbed and some diffused, hence reducing the amount that is transmitted. For example, Figure 5 shows that simply offsetting hallway doors can decrease the sound transmitted from one space to another through the doors. Separating windows will have a similar effect (see Figure 6).

Any wall penetration will potentially transmit sound. Therefore, plan to eliminate penetration whenever possible (see Figure 7). When unavoidable, partial wall penetrations such as electrical boxes should be completely sealed with joint sealant. Through-wall openings should be completely sealed, after first filling gaps with foam, cellulose fiber, glass fiber, ceramic fiber or mineral wool. See Sound Transmission Class Ratings of Concrete Masonry Walls, TEK 13-01D, for a more complete discussion of minimizing sound transmission through wall penetrations.

Finally, building heating and cooling ducts offer a potential noise pathway throughout a building. There are many ways to absorb or dissipate this noise, including acoustic linings and splitters to help break up and disperse the sound energy (see Figure 8). Any changes to the building’s ductwork will also potentially impact heating and cooling distribution. These effects should be considered during the HVAC system design.

Figure 3—Plan the Building Layout to Minimize Common Walls
Figure 4—Use Mirror Floor Plans
Figure 5—Offset Doors Opening onto the Same Hallway
Figure 6—Move Windows Farther Away from Common Wall
Figure 7—Minimize Wall Penetrations
Figure 8—Acoustic Controls for Heating and Cooling Ducts

REFERENCES

  1. 2003 International Building Code. International Code Council, 2003.
  2. 2006 International Building Code. International Code Council, 2006.
  3. Sound Transmission Class Ratings of Concrete Masonry Walls, TEK 13-01D. Concrete Masonry & Hardscapes Association, 2012.
  4. Standard Test Method for Sound Absorption and Sound Absorption Coefficients by the Reverberation Room Method, ASTM C423-07. ASTM International, 2007.
  5. Standard Method for Determining the Sound Transmission Class Rating for Masonry Walls, TMS 0302-07. The Masonry Society, 2007.

TEK 13-02A, Revised 2007. CMHA and the companies disseminating this technical information disclaim any and all responsibility and liability for the accuracy and the application of the information contained in this publication.

Balanced Design Fire Protection for Multifamily Housing

  • August 2018

INTRODUCTION

The application of balanced design principles is particularly important in multifamily residential buildings. The risk of fires in apartments and condominiums is high because of the numerous kitchens, furnaces, hot water heaters, and other causes of residential fires. In addition, there is always a potential for sleeping occupants, children, and others who may be at a disadvantage for evacuating quickly. Fire safety in multifamily housing requires an understanding of the hazards involved, so that both the potential for fire and the threat to life-safety during a fire are minimized. The purpose of balanced design is to protect life and property during a fire. Death and injury from fire is caused by asphyxiation from toxic smoke and fumes; burns from direct exposure to the fire; heart attacks caused by stress and exertion; and impact due to structural collapse, explosion and falls. Life safety in multifamily housing is influenced by the design of the building, its fire protection features, and by the materials, building contents, quality of construction, and maintenance.

BALANCED DESIGN

Balanced design relies on three complementary life safety systems to reduce the risk of death due to fire:

  • a detection system to warn occupants of a fire
  • a containment system to limit the extent of fire and smoke
  • an automatic suppression system to control the fire until it can be extinguished.

Each of these essential systems contributes to lowering the risk of death and injury from fire in multifamily housing. The three balanced design components complement each other by providing fire protection features that are not provided by the other components. Some features of each balanced design component are intended to be redundant, so that in the event that one system is breached, or fails to perform, the other components continue to provide safety.

Although not a tangible element in fire protection, a strong education program should be an integral part of any good fire protection plan in addition to the physical components of a balanced design system.

DETECTION

Accurate early warning is the first line of defense against the slow smoldering fire, typical in dwelling units with a low heat release rate that doesn’t activate a sprinkler head. Detectors that respond to light smoke are important from a life-safety standpoint to alert occupants so they can evacuate.

Other detection or alarm systems may be used to notify the fire department, thus decreasing response time, expediting rescue operations, and limiting the resulting fire spread and property damage. Detectors wired to a central alarm and installed in corridors and common areas notify all building occupants, permit timely and orderly evacuation, and decrease the potential for injury and death.

The National Fire Protection Association (NFPA) National Fire Alarm Code, NFPA 72 (ref. 3), covers minimum performance, location, installation, testing and maintenance of detectors. The Standard includes heat, smoke, flame and gas sensing fire detectors.

The most common detector used in multifamily housing is the smoke sensing fire detector. Detectors should be wired into a continuous power supply. Their location in multifamily housing is determined in accordance with the building code.

Each dwelling unit should be equipped with detectors in all sleeping rooms and in areas adjacent to all sleeping rooms, and on each level of the building, including the basement. The amount of air movement and obstructions within the space, such as partitions, ceiling height, and other factors, will guide the fire protection engineer in the proper selection of the detector location.

The performance of detectors is vulnerable to unpredictable malfunctions, among which are lack of maintenance due to human error and neglect, faulty power supply, and even acts of sabotage by arsonists. Young children, the disabled, elderly, and the deaf may not be able to respond to auditory alarms.

Tests on smoke detectors (ref. 4) indicate the need for a regularly scheduled maintenance and testing program, as well as the periodic replacement of some components.

SUPPRESSION

The function of automatic sprinkler systems is to control a fire at the point of origin. While not designed to extinguish a fire, residential sprinklers have been shown to be very reliable and effective in controlling a fire in the room of origin until it can be extinguished. Sprinklers reduce the likelihood of flashover. Flashover, the rapid ignition of volatile gasses, is particularly hazardous in exit corridors. Suppression of a fire allows access to the building to permit rescue and fire fighting efforts to proceed. Sprinklers are credited with preventing multiple deaths in fires.

The NFPA maintains minimum standards for the design and installation of sprinkler systems. Sprinkler systems for multifamily housing more than four stories in height are covered by NFPA Standard 13 (ref. 1). NFPA Standard 13R (ref. 2) covers the installation of sprinkler systems in multifamily housing up to and including four stories in height. When the interior construction or building contents contain a large amount of combustibles, sprinkler systems should meet the NFPA 13 Standard, regardless of height, to ensure protection in attics, closets, and other concealed spaces built with combustible materials, and to provide additional suppression in all areas due to the higher fuel loadings.

The NFPA Standards cover the design, installation, acceptance testing, and maintenance of sprinkler systems. In addition, there are specific spaces which are not required by NFPA 13R to be sprinklered. The Standards require an adequate water supply and a piping system designed to deliver sufficient water to the sprinkler head. Sprinkler head requirements ensure proper water coverage based on the room dimensions, area to be covered, and fuel loading. The Standards also list exceptions for specific spaces which are not required to be sprinklered. Once installation is complete, the Standards require inspection and acceptance of the system’s piping, valves, pumps and tanks. Testing also includes verification of adequate water flow to the sprinkler heads. After the sprinkler system is in use, it must be maintained; however, specific maintenance requirements and frequency of maintenance are not specified by the Standards.

Performance of automatic sprinklers can be vulnerable to system failures due to inadequate maintenance and inspection, or inadequate water supply. Sprinklers are not intended to control electrical and mechanical equipment fires or fires of external origin, such as fires from adjacent buildings, trash fires, and brush fires. Fires in concealed spaces, including some attics, closets, flues, shafts, ducts, and other spaces where sprinkler heads are not required to be installed, can compromise life safety due to the spread of toxic fumes and smoke. Inadequate water supply can occur due to low pressure in the municipal water system, broken pipes due to earthquakes or excavation equipment, explosions, freezing temperatures, closed valves due to human error, arson or vandalism, corrosion of valves, pump failure due to electrical outage, and lack of system maintenance.

COMPARTMENTATION

Compartmentation contains a fire until it can be brought under control by fire fighters as illustrated in Figure 1. Compartmentation limits the extent of fire by dividing a building into fire compartments enclosed by fire walls or fire separation wall assemblies, and by fire rated floors and ceilings. Compartments also minimize the spread of toxic fumes and smoke to adjacent areas of a building. Conflagrations beyond the fire compartment are prevented by limiting the total fuel load contributing to the fire. Compartmentation provides safe areas of refuge for handicapped, young, elderly, incapacitated and other occupants who may not be capable of unassisted evacuation. Compartmentation also provides safe areas of refuge for extended periods, where evacuation is precluded due to smoke filled exit ways or blocked exits. Compartmented construction provides protection for fire and rescue operations. Highly hazardous areas, such as mechanical, electrical or storage rooms, can be isolated by fire walls from other occupied areas of a building. Fire separation walls and floor/ceiling assemblies between dwelling units in multifamily housing afford protection from fires caused by the carelessness of other occupants.

Each compartment is enclosed by fire resistive components. Floor and wall elements forming the boundaries of each compartment should have a fire resistance rating of at least two hours, and should be constructed of noncombustible materials that are capable of preserving the structural integrity of the building throughout the duration of the fire.

Openings through compartment boundaries should be protected openings. Doors should be self closing when fire or smoke is detected. In multifamily housing, each dwelling unit should form a separate compartment. In addition, interior exit ways, as well as storage, electrical, and mechanical rooms, should be separate compartments. Exterior walls should be fire rated to form a barrier to the penetration of exterior fires and to contain interior fires.

The value of compartmentation could be reduced when joints between floors and walls, typically exterior curtain walls, or between walls and ceilings, are not properly fire-stopped. Damage caused by equipment, abuse, or the installation of utilities which are not properly sealed, can allow the passage of smoke and gas. Unsealed openings around penetrations can also allow the convective spread of smoke. Self-closing mechanisms on doors in compartment walls may fail if not maintained, or if blocked open.

PROPERTY PROTECTION

The initial cost of providing fire safety can be significant; however, balanced design offers advantages which offset initial costs. The higher level of protection for both the structure and its contents limits the potential loss due to fire. Immediate and long term savings will be reflected in lower insurance rates for both the building and its furnishings. Balanced design limits both fire and smoke damage of the building’s contents to the compartment of fire origin. Noncombustible compartment boundaries limit damage to the structure itself and reduce repair time following a fire. Repair is generally nonstructural, but may include the replacement of doors and windows; electrical outlets, switches and wiring; heating ducts and registers; and floor, wall and ceiling coverings.

SUMMARY

Fire protection engineering is as much an art as it is a science. The number of unknowns and potential fire propagation scenarios are numerous. Fire protection is, therefore, generally based more on risk assessment than precise calculation. Currently, building code prescriptive criteria, (ref. 5, 6) along with an understanding of the science of fire protection, guides the designer in addressing fire safety.

Some of the more significant fire safety issues requiring consideration are listed in Table 1, along with the effectiveness of each component of balanced design. As shown by the table, there may be more than one component which is considered effective in mitigating a particular hazard. Since none of the components are fail-safe, overlapping functions are needed to provide the required level of safety. In addition, there are some functions listed in the table which are addressed by only one component of balanced design. The appendix of NFPA Standard 13R (ref. 2) also recognizes the need for compartmentation and detection, along with sprinklers, to ensure a reasonable degree of life-safety protection.

There is a general agreement among the engineering and scientific communities that the desired approach to improving fire safety in buildings is through computer modeling. Limited success to date has been achieved in developing a system (ref. 7) that will assess risk and design protection levels for each of the three components of balanced design. Future efforts will be directed through the government and the private sector in a cooperative effort to develop this tool.

REFERENCES

  1. Installation of Sprinkler Systems, NFPA 13, National Fire Protection Association, 2007.
  2. Standard for the Installation of Sprinkler Systems in Residential Occupancies up to and Including Four Stories in Height, NFPA 13R, National Fire Protection Association, 2007.
  3. National Fire Alarm Code, NFPA 72 National Fire Protection Association, 2007.
  4. Why We Need to Test Smoke Detectors, Leon Cooper, Fire Journal, National Fire Protection Association, November 1986.
  5. Life Safety Code, NFPA 101, National Fire Protection Association, 2006.
  6. Standard on Types of Building Construction, NFPA 220, National Fire Protection Association, 2006.
  7. Fire Hazard Assessment Method, Hazard I, NIST Handbook No. 146, National Institute of Standards and Technology, U.S. Department of Commerce, 1989.

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

  1. Passive Solar Design, TEK 06-05A, Concrete Masonry & Hardscapes Association, 2006.
  2. Basement Manual: Design and Construction Using Concrete Masonry, CMU-MAN-002-01, Concrete Masonry & Hardscapes Association, 2001.
  3. EERE Consumers Guide: Site-Specific Factors for Earth Sheltered Home Design. U. S. Department of Energy, 2005.
  4. Earth-Sheltered Home Design. U. S. Department of Energy, http://www.eere.energy.gov/consumer/your_home/designing_rem deling/index.cfm/mytopic=10100.
  5. Forowicz, T. Z. An Anlaysis of Different Insulation Strategies for Earth-Sheltered Buildings. ASHRAE Transactions, Vol. 100 Part 2, 1994.
  6. 2005 ASHRAE Handbook Fundamentals. American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc., 2005.
  7. 2003 International Residential Code for One and Two Family Dwellings. International Code Council, 2003.

Passive Solar Design

  • August 2018

INTRODUCTION

Passive solar design involves utilizing a building’s basic elements walls, windows and floors—to produce a comfortable environment with less reliance on mechanical heating and cooling. Passive solar systems can provide space heating, natural ventilation, cooling load avoidance, daylighting and water heating. The U. S. Department of Energy estimates that 30 to 50% energy cost reductions are economically realistic in new office design with an optimum mix of energy conservation and passive solar design strategies (ref. 1). In addition, most passive solar design strategies integrate well with active solar applications such as photovoltaics.

Concrete masonry plays a vital role in effective passive solar design, by providing thermal mass to absorb and slowly release solar heat. Without sufficient thermal mass, passive solar buildings can overheat and be uncomfortable.

It is most economical to evaluate passive solar strategies early in the design process. The rules of thumb included in this TEK are intended as a starting point for determining preliminary size and location for concrete masonry and glazing. As the design progresses, a more detailed analysis should be performed, preferably using software designed to accommodate passive solar interactions. Some appropriate software programs are briefly discussed near the end of this TEK.

PASSIVE SOLAR IN BUILDING CODES AND LEED

Renewable energy sources, such as passive solar, are typically not explicitly included in energy code criteria. Often, a passive solar building will comply with energy code requirements when the passive solar elements are neglected. Where this is not the case, for example where the prescriptive limit on glazing area is exceeded, most building codes allow compliance using an analysis based on whole building performance. For residential buildings three stories or less in height, Chapter 4 of the International Energy Conservation Code (IECC, ref. 2) describes the criteria for an annual energy analysis to demonstrate compliance.

For commercial and high-rise residential buildings, IECC compliance falls under section 806, Total Building Performance, or via Chapter 7 which references Energy Standard for Buildings Except Low-Rise Residential Buildings, ASHRAE/IESNA 90.1-2001 (ref. 3). Section 11 of Standard 90.1, Energy Cost Budget Method, is used for passive solar compliance. Note that a 2004 edition of ASHRAE 90.1 is also available, but the energy cost budget provisions are essentially the same as those in the 2001 edition. As for IECC Chapter 4, these sections define criteria for the annual whole-building analysis required to demonstrate compliance.

In the LEED program (ref. 4), passive solar systems are included under Energy and Atmosphere Credit 1, Optimize Energy Performance. This credit again references the energy cost budget method defined in Section 11 of ASHRAE/IESNA Standard 90.1 for demonstrating the building energy performance. Note that E&A Credit 2, Renewable Energy, applies only to renewable energy systems that generate power, such as photovoltaics, biomass and wind turbines.

ELEMENTS OF A PASSIVE SOLAR DESIGN

The components of a passive solar design are familiar parts of any building. In a passive solar building, however, these elements are carefully chosen, sized and located to work together to provide comfort. The function of each of these components is briefly described here. Some general guidance regarding sizing and location is included in the section Passive Solar Design Rules of Thumb.

Thermal Mass

Thermal mass in passive solar design provides three functions: it quickly absorbs solar heat to help avoid overheating when the sun shines; it stores the solar heat; and it slowly releases the heat to provide warmth after the sun sets. Concrete masonry walls and concrete paver floors are very efficient thermal storage mediums, and are commonly used in passive solar buildings to provide these functions. Masonry location and thickness are important to passive solar design, as are the conduction, specific heat and density. As these three properties increase, the heat storage effectiveness generally increases accordingly.

However, very high conductances should be avoided since this can shorten the time lag for heat delivery.

One important performance measure of passive solar buildings is the ability to maintain comfortable indoor temperatures. The amplitude of the indoor temperature swing is determined by the amount of effective thermal mass in the building. As the amount of thermal mass increases, the daily indoor temperature swing typically decreases.

Glazing

Glazing allows solar heat and light into the building. Choice of particular glazing products, sizes and locations will vary with the desired heat gain, cooling load avoidance and daylighting needs. These may vary within the building according to how the interior spaces are used. For example, because of glare, areas such as lobbies and atria may be more appropriate on a south-facing wall with a large amount of direct sunlight, than, for example, an office space.

Shading

Appropriate shading helps prevent solar heat gain during the summer. Shading may include permanent overhangs or porch roofs, moveable awnings, shutters, vegetation to shade east and west-facing windows, and/or limiting east/west glass.

Ventilation

Venting can rid the building of heat when the thermal mass is saturated. It can also provide outdoor air to cool the building when the outside air is cooler than the building’s thermostat setting, such as by precooling the building at night. Ventilation can be accomplished using natural ventilation or using an exhaust fan tied to a thermostatic control.

Types of Passive Solar Designs

Passive solar designs can generally be classified as one of three types, depending on where the solar heat is collected relative to where it is used: direct gain, indirect gain or isolated gain. The basic components are illustrated in Figure 1.

Direct Gain Systems

In a direct gain space, solar energy penetrates directly into the space where it is stored and used. Direct gain systems are the simplest to install since only windows and mass are required. Figure 1a shows the proper use of thermal mass in the walls and on the floor. Heat is collected and distributed by transmission through the windows, absorption at the mass surface, and convection and radiation within the room. Using sufficient thermal mass improves performance and comfort.

Indirect Gain

With indirect gain, a thermal storage material is used between the glazing and the space to be heated to collect, store and distribute solar radiation. An example is the trombe wall (see Figure 1b). A trombe wall uses a south-facing masonry wall faced with glazing placed 3/4 to 2 in. (19-51 mm) from the masonry. Heat from sunlight passing through the glass is absorbed by the masonry and slowly transferred through the wall to the interior space. Shading and/or ventilation are used to prevent unwanted heat gains during warmer periods. Vents at the top and bottom of a trombe wall are sometimes included to set up a convective current for passive cooling.

Isolated Gain

Isolated gain systems, such as sunspaces, collect solar energy in an area that can be closed off from the rest of the building. In addition to thermal mass floors, sunspaces typically use concrete masonry walls for thermal storage and as a heat transfer “valve” between the sunspace and the living or working space. Sunspace heat can be moved through vents with backdraft dampers to prevent improper flow. A fan, doors and/or windows can also be used to circulate warm air to the living space.

Because of the potential for overheating, care must be used when designing with sloped (i.e., overhead) glazings. Vertical glazings and pop-up skylights can be used with only a small decrease in performance. Vertical glazing is less expensive than sloped glazing, and overheating is more easily prevented.

PASSIVE SOLAR DESIGN RULES OF THUMB

Rules of thumb are useful early in the design process, as a first step in laying out the building and sizing the systems and materials. The rules of thumb listed below are most appropriate for buildings with skin-dominated heating loads, such as residential and small commercial buildings. Note that many of these design considerations involve compromises. For example, allowing maximum solar heat gain while minimizing summer heat gain. The designer should consider the specifics of the site and climate when evaluating appropriate passive solar design strategies. Software is particularly effective for evaluating these interactions for a particular building. General suggestions for successful passive solar performance include:

  1. Building orientation. Ideally, the building south wall should face within 15 degrees of true south. With this orientation, the building receives maximum winter and minimum summer heat gains. Between 15 and 30 degrees east or west of true south, performance tends to be reduced about 15 percent from the optimum.
  2. Buffer the north side of the building. Place rooms with low heating, lighting and use requirements, such as utility rooms, storage rooms, and garages on the north side of the building to buffer the other spaces. This can reduce the normally higher heat loss through north walls while not interfering with solar access.
  3. Match the solar heating system to the room use. Consider occupancy patterns when choosing a system: what are the heating, daylighting and privacy requirements of the room? For example, a bedroom requires privacy and needs heat after sunset, so a thermal storage wall might be the logical choice. A living room, on the other hand, needs daytime and early evening heat and has higher lighting requirements; therefore, a direct gain system or sunspace may be more appropriate.
  4. Include adequate thermal mass. For buildings with southfacing glass area more than 7% of the floor area, additional thermal mass must be included to absorb heat and maintain comfort. Thermal mass, such as concrete masonry walls and concrete paver floors, should be relatively thin (2 to 4-in. (51 to 102-mm) thick) to allow heat absorption and release within a 24-hour cycle; and should be spread over a large area to help prevent localized hot or cold spots.

Eight-in. (203-mm) fully grouted concrete masonry should be used if the wall is used as a north-south division wall separating two direct gain rooms. Such a wall can store heat on both sides, optimizing the mass storage. Do not fill the cores of these walls with sand, soil or insulation.

For trombe walls, the concrete masonry wall is typically 8 to 16 in. (203 to 406 mm) thick, depending on the desired time lag for heat distribution indoors.

Minimum recommended ratios of thermal mass area to additional glass area (i.e., south-facing glass area > 7%) are (ref. 5):

  • 1: 5.5 for floor in direct sunlight,
  • 1:4 for floor not in direct sunlight, and
  • 1:8.3 for wall and ceilings.

5. Distribute the thermal mass throughout the room. In direct gain systems, the primary collection mass is placed in direct sunlight. In addition to this mass, comfort is improved if mass is distributed evenly around the room because localized hot or cold spots are less likely to develop. Performance is relatively the same whether the mass is located on the east, west or north walls, or in the floor. The mass should be distributed over an interior surface area approximately equal to six times the solar glass area.

6. Avoid “insulating” thermal mass. Rugs or carpets in the solar collection space will significantly impact thermal mass performance. In general, an exposed strip of massive floor about 8 ft (2.4 m) wide provides a good floor collection area.

7. Select an appropriate thermal mass color. Masonry walls can be any color in direct gain systems, although the mass should be somewhat darker (0.5 < a < 0.8) than the low-mass materials. (Absorptivity, a, ranges from 0 to 1, indicating the percentage of incident solar energy that is absorbed. a = 1 indicates 100% absorption) The absorptivity of natural or colored concrete masonry falls in this range without paints or special treatments. Mass walls that are too dark (0.8 < a < 1.0), can result in high surface temperatures where surfaces are exposed directly to the sun, and less absorption elsewhere on the wall. Masonry floors, on the other hand, should be dark (0.7 < a < 1.0) to increase the absorption of the concrete pavers or masonry units and to counter the tendency of the heat to be released too rapidly to the atmosphere. A matt floor finish will maximize absorption and reduce glare. Thermal storage walls should be dark (a > 0.8) or coated with a selective surface material, such as a metallic film specifically designed to maximize absorption and minimize heat loss due to radiation back towards the glass. Materials without significant thermal mass, such as frame walls, should be lighter in color.

  1. Choose appropriate glass. Windows are typically rated by their solar heat gain coefficient (SHGC) and conductance (U-factor). Regardless of climate, the U-factor should be as low as possible (0.35 or less), to minimize conductive heat loss through the windows. For south-facing glass in most climates, choose windows with a SHGC as high as possible (0.6 or higher) to allow maximum heat gain during the winter, and rely on overhangs or other shading to limit summer sun. In cooling climates, such as south Florida, choose windows with a SHGC as low as possible.
  2. Use appropriate window shading. Windows facing within about 30o of true south can be shaded with properly sized overhangs. Figure 2 shows guidelines for sizing the overhangs to allow sunlight entry from about mid September through mid-March (software is also available for sizing overhangs). Off-south wall orientations reduce overhang effectiveness.

    East- and west-facing glass can be a significant source of heat gain and glare year-round, because of low morning and evening sun angles. Of the two, west-facing glass is more of a concern, because afternoons are typically hotter than mornings. There are several strategies to address these issues: limit the area of east- and west-facing glass; use wide overhangs (such as porch roofs; smaller overhangs will not be effective); use evergreens for shading; or use glass that blocks solar heat (although this may require different glass types for different walls of the building).
  3. Landscaping. Consider solar access and prevailing wind patterns when choosing trees and shrubs. Issues to consider include: shading of south-, east- and west-facing glass; channeling summer breezes; summer shading of the roof and paved areas; and blocking prevailing winter winds. Because leafless deciduous trees can block as much as 30% of winter solar energy, trees should not be placed where they block the south-facing windows in locations where significant winter solar heating is expected. However, in climates where summer heat is a significant problem, trees on the south-facing side may be appropriate.

SOFTWARE TOOLS

Software to evaluate passive solar buildings should include an annual whole-building analysis, and be able to correctly model solar gains and thermal mass. Programs such as DOE2 and BLAST are very comprehensive and well-documented. However, these programs require a high level of user expertise and can be cumbersome to use.

Energy-10 is a conceptual design tool focused on making whole building trade-offs during early design phases for residential and small commercial buildings (less than 10,000 ft2 (930 m2 ) floor area). The program performs an hourly annual whole-building energy analysis, including dynamic thermal and daylighting calculations. Outputs include a summary table, detailed tabular results and 20 graphical outputs.

EnergyPlus builds on the capabilities of BLAST and DOE2, with some additional simulation capabilities such as time steps of less than an hour. Input and output are via ASCII text files, although the program was developed to facilitate thirdparty user-friendly interfaces (see http://www.eere.energy.gov/ buildings/energyplus/ for available interfaces).

These programs are described on the Department of Energy website, http://www.eere.energy.gov/buildings/tools_directory. The website contains a list of over 300 building analysis programs, searchable by name, subject or platform. The site also includes information on program capabilities, input, output, user expertise required, how to obtain the software, as well as strengths and weaknesses.

REFERENCES

  1. Passive Solar Design. U. S. Department of Energy, www.eere.energy.gov/buildings/info/design/integratedbuilding/passive.html.
  2. 2003 International Energy Conservation Code. International Code Council, 2003.
  3. Energy Standard for Buildings Except Low-Rise Residential Buildings, ASHRAE/IESNA 90.1-2001/2004. American Society of Heating, Refrigerating and AirConditioning Engineers, Inc., 2001/2004.
  4. LEED for New Construction and Major Renovations, LEED-NC version 2.2. U. S. Green Building Council, 2005.
  5. Green Building Guidelines: Meeting the Demand for LowEnergy, Resource-Efficient Homes. Sustainable Buildings Industry Council, 2004.
  6. ASHRAE Handbook, Fundamentals. American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc., 2005.

Residential Details for High Wind Areas

  • August 2018

INTRODUCTION

High winds subject buildings to large horizontal forces as well as to significant uplift. Reinforced concrete masonry is well suited to resist the large uplift and overturning forces due to its relatively large mass.

High wind provisions generally apply to areas where the design wind speed is over 100 mph (161 km/hr) and over three second gust as defined by ASCE 7 (ref. 10). The enclosed details represent prescriptive minimum requirements for concrete masonry buildings, based on Standard for Hurricane Resistant Residential Construction (ref. 3).

CONTINUOUS LOAD PATH

Connections between individual building elements—roof, walls, floors and foundation—are critical to maintaining structural continuity during a high wind event. The critical damage to buildings in such events typically occurs due to uplift on the roof, resulting in the loss of crucial diaphragm support at the top of the wall. A primary goal for buildings subjected to high winds is to maintain a continuous load path from the roof to the foundation. This allows wind uplift forces on the roof to be safely distributed through the walls to the foundation. If one part of the load path fails or is discontinuous, building failure may occur.

Proper detailing and installation of mechanical connectors is necessary for maintaining continuous load paths. Note that in order for connectors to provide their rated load capacity, they must be installed according to the manufacturer’s or building code specifications. In coastal areas, corrosion protection is especially important due to the corrosive environment. Note that water penetration details are not specifically highlighted in the following details. The reader is referred to references 7 through 9 for more information on preventing water penetration in concrete masonry walls. In addition to a continuously reinforced bond beam at the top of the wall around the entire perimeter of the building, vertical reinforcement must be placed throughout a wall to resist the high uplift loads and provide continuity, including: at corners and wall intersections; on each side of openings wider than 6 ft (1,829 mm); at the ends of shear segments; and where girders or girder trusses bear on the concrete masonry wall (refs. 3, 4). Each of the exterior walls on all four sides of the building and all interior walls designed as shear walls must have at least one 2 ft (610 mm) minimum section of wall identified as a shear segment to resist the high lateral loads. Longer shear segments are more effective and are recommended where possible or required by design. See Figure 1 for a summary of reinforcement requirements (ref. 3).

Reinforcement must be properly spliced to provide load path continuity. Using allowable stress design, a splice length of 40 bar diameters is required by Building Code Requirements for Masonry Structures (ref. 1) for Grade 40 reinforcement and 48 bar diameters for Grade 60 reinforcement. If the wall was designed assuming Grade 40 and Grade 60 was used for construction, however, the 40 bar diameter lap splice may still be used. See Steel Reinforcement for Concrete Masonry, TEK 12-04D (ref. 5) for standard hook requirements.

DETAILS

Exterior Loadbearing Wall

Figure 2 shows a typical loadbearing wall with a floating floor slab. Vertical reinforcement should be placed in the center of the concrete masonry cores to adequately resist both positive and negative wind pressures. Bond beam depth and minimum horizontal reinforcement varies with design wind velocity, ceiling height, roof truss span and spacing of vertical wall reinforcement. Since wind suction forces on the leeward side of a building can be essentially as high as the pressure forces on the windward side, limitations are placed on the height above grade. However, if the slab is laterally supported and tied to the concrete masonry foundation wall as shown in Figure 3, the foundation wall may be extended to 8 ft (2,440 mm) above grade (ref. 3).

Roof Truss Anchor

Figure 4 shows a typical roof truss anchor cast into the bond beam of a concrete masonry bearing wall. The required anchor load capacity depends on the design wind speed as well as the roof truss span. In addition to being rated for uplift, the anchor must be rated for horizontal forces parallel to the wall (in-plane) and perpendicular to the wall (out-of-plane).

Often, the direct embedded roof truss anchor method of connecting the roof to walls is preferred over the bolted top plate and hurricane clip method, as it generally has greater capacity and fewer connections. Additionally, the nail area available for the hurricane clip is limited by the thickness of the top plate.

Bolted Top Plate

As an alternate to the roof truss anchor, a bolted top plate may be used for the roof to wall connection (see Figure 5); however, anchor bolt spacing must be reduced (24 in. (610 mm) maximum) because the top plate is loaded in its weak direction. The detail illustrates several different connector types that are commonly used to connect the truss to the top plate.

Gable End Walls

Because of their exposure, gable end walls are more prone to damage than are hipped roofs unless the joint at the top of the end wall and the bottom of the gable (see Figure 6b) is laterally supported for both inward and outward forces. Figure 6a shows a continuous masonry gable end wall using either a raked concrete bond beam or a cut masonry bond beam along the top of full height reinforced concrete masonry gable end walls.

As an alternative, a braced gable end wall can be constructed as shown in Figure 6b by stopping the masonry of the gable end at the eave height and then using conventional wood framing to the roof diaphragm. However, unless the end wall is properly braced to provide the necessary lateral support as shown in Figure 6b, this results in a weak point at the juncture of the two materials with little capacity to resist the high lateral loads produced by high winds. The number and spacing of braces depends on design wind speed, roof slope and roof span (ref. 2, 3, 6).

Gable End Wall Overhangs

Figure 7a shows a continuously reinforced castin-place concrete rake beam along the top of the gable end wall. The beam is formed over uncut block in courses successively shortened to match the slope of the roof. A minimum of 4 in. (102 mm) is needed from the highest projected corner of block to the top of the beam. Reinforcement that is continuous with the bond beam reinforcement in the side walls is placed in the top of the beam. In this detail, an outlooker type overhang is shown where the rake beam is constructed 3½ in. (89 mm) lower than the trusses so that a pressure treated 2 x 4 (38 x 89 mm) can pass over it. A ladder type overhang detail also can be used with the concrete rake beam where the beam is constructed to the same height as the trusses similar to that shown for the cut masonry rake beam in Figure 7b.

Figure 7b shows a continuously reinforced cut masonry rake beam along the top of the gable end wall. Masonry units are cut to conform to the roof slope at the same height as the roof trusses. A 2 ¾ in. (70 mm) deep notch is cut into the tops of the concrete masonry webs to allow placement of reinforcement that is continuous with the bond beam reinforcement in the side walls. A minimum of height of 4 in. (102 mm) is needed for the cut masonry bond beam. In this figure, a ladder type overhang is shown. However, an outlooker type overhang detail can be used similar to that shown for the cast-in-place concrete rake beam in Figure 7a.

REFERENCES

  1. Building Code Requirements for Masonry Structures, ACI
    530-02/ASCE 5-02/TMS 402-02. Reported by the Masonry
    Standards Joint Committee, 2002.
  2. The Guide to Concrete Masonry Residential Construction
    in High Wind Areas. Florida Concrete & Products
    Association, Inc., 1997.
  3. Standard for Hurricane Resistant Residential Construction,
    SSTD 10-99. Southern Building Code Congress
    International, Inc., 1999.
  4. 2000 International Building Code. International Code
    Council, 2000.
  5. Steel Reinforcement for Concrete Masonry, TEK 12-04D.
    Concrete Masonry & Hardscapes Association, 2002.
  6. Annotated Design and Construction Details for Concrete
    Masonry, CMU-MAN-001-23. Concrete Masonry &
    Hardscapes Association, 2003.
  7. Design for Dry Single-Wythe Concrete Masonry
    Walls, TEK 19-02B. Concrete Masonry & Hardscapes
    Association, 2012.
  8. Flashing Strategies for Concrete Masonry Walls, TEK 19-
    04A. Concrete Masonry & Hardscapes Association, 2003.
  9. Flashing Details for Concrete Masonry Walls, TEK 19-05A.
    Concrete Masonry & Hardscapes Association, 2008.
  10. Minimum Design Loads for Buildings and Other
    Structures, ASCE 7-02. American Society of Civil
    Engineers, 2002.

Concrete Masonry Residential Details

  • August 2018

INTRODUCTION

Concrete masonry homes reflect the beauty and durability of concrete masonry materials. Masonry housing provides a high standard of structural strength, design versatility, energy efficiency, termite resistance, economy and aesthetic appeal.

A wide range of architectural styles can be created using both architectural concrete masonry units and conventional units. Architectural units are available with many finishes, ranging from the rough-hewn look of split-face to the polished appearance of groundface units, and can be produced in many colors and a variety of sizes. Concrete masonry can also be finished with brick, stucco or any number of other finish systems if desired. Concrete masonry’s mass provides many consumer benefits. It has a high sound dampening ability, is energy efficient, fire and insect proof, durable and can easily be designed to resist hurricane-force winds and earthquakes.

WALLTYPES

Figures 1 through 3 illustrate a few of the construction options available for concrete masonry home construction, some of which are described in more detail below. Both top plate/anchor bolt and embedded strap anchor roof connections are shown and can be used interchangeably, along with several foundation types. See also 05 07A Floor and Roof Connections to Concrete Masonry Walls and 05-03A Concrete Masonry Foundation Wall Details (refs. 2, 3) for additional alternatives.

Single wythe walls offer the economy of providing structure and an architectural facade in a single building element. They supply all of the attributes of concrete masonry construction with the thinnest possible wall section. To enhance the performance of this wall system, two areas in particular need careful consideration during design and construction—water penetration resistance and energy efficiency. Design for water resistance is discussed in detail in References 4 through 6. A full discussion of options for energy efficient concrete masonry walls is contained in Insulating Concrete Masonry Walls (ref. 7).

The use of exterior finish systems lends itself to exterior insulation. Figure 1 shows an exterior insulation system, including a water drainage plane and stucco. Stucco can also be applied directly to the exterior block surface and used in conjunction with integral or interior insulation. Note that local codes may restrict the use of foam plastic insulation below grade in areas where the hazard of termite damage is high.

Figure 2 shows a residential wall section with exposed concrete masonry on the exterior and a furred-out and insulated interior. Concrete masonry can be exposed on the interior as well. In this case, integral insulation (placed in the masonry cores) can be used as required.

Figure 3 shows exterior siding with insulation installed between furring. Wood or vinyl siding, as shown, is typically attached using exterior wood furring strips which have been nailed to the masonry.

Cavity wall details are shown in TEK 05-01B, Concrete Masonry Veneer Details (ref. 8).

REFERENCES

  1. Annotated Design and Construction Details for Concrete
    Masonry, CMU-MAN-001-03. Concrete Masonry &
    Hardscapes Association, 2003.
  2. Floor and Roof Connections to Concrete Masonry Walls,
    05-07A. Concrete Masonry & Hardscapes Association,
    2001.
  3. Concrete Masonry Foundation Wall Details, TEK 05-03A.
    Concrete Masonry & Hardscapes Association, 2003.
  4. Water Repellents for Concrete Masonry Walls, TEK 19-01.
    Concrete Masonry & Hardscapes Association, 2002.
  5. Design for Dry Single-Wythe Concrete Masonry
    Walls, TEK 19-02B. Concrete Masonry & Hardscapes
    Association, 2012.
  6. Flashing Details for Concrete Masonry Walls, TEK 19-05A.
    Concrete Masonry & Hardscapes Association, 2000.
  7. Insulating Concrete Masonry Walls, TEK 06-11A. Concrete
    Masonry & Hardscapes Association, 2010.
  8. Concrete Masonry Veneer Details, TEK 05-01B. Concrete
    Masonry & Hardscapes Association, 2003.