BIA notes 28D.pdf

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TECHNICAL NOTES on Brick Construction 12007 Sunrise Valley Drive, Suite 430, Reston, Virginia 20191 | www.gobrick.com | 703-620-0010

28D June

Brick Veneer/Concrete Masonry Walls Abstract: This Technical Note presents design, material and construction information for anchored brick veneer on concrete masonry backing. Description of properties, theories of structural design and proper detailing are presented. Refer to Technical Notes 28 and 28B for specific information related to drained wall assemblies with non-masonry backing.

Key Words: anchored, brick, concrete masonry, design, expansion joints, flashing, thermal resistance, ties, veneer.

Drainage/Air Space

• 2 in. (51 mm) minimum air space recommended; 1 in.

(25.4 mm) minimum air space* required

• For brick veneer, do not exceed 6⅝ in. (168 mm) between back of veneer and face of inner wythe unless ties are designed (see Ties)

• For non-composite multi-wythe walls, do not exceed 4½ in. (114 mm) maximum between back of outer wythe and face of inner wythe

• Completely fill air space below wall base flashing with mortar or grout

• Where continuous insulation is placed in drainage cavity, provide no less than a nominal 1 in. (25.4 mm) clearance between the back of outer wythe and exterior face of insulation

* An air space is allowed to be a 1 in. (25.4 mm) nominal dimension in the IRC and a 1 in. (25.4 mm) specified dimension in the IBC to account for construction tolerances.

Flashing

• Install at base of wall, at shelf angles, above window heads, below window sills and at other locations where air space is interrupted

• Extend vertical leg of flashing a minimum of 8 in.

(203 mm) and terminate in bed joint of inner wythe or with termination bar

• Where flashing laps are required, provide minimum 6 in.

(152 mm) overlap and seal

• Where flashing is discontinuous, form end dams by turning ends up at least 1 in. (25.4 mm) into a head joint

Weeps

• Place immediately above flashing

• Open head joint weeps preferred. Spacing recommended to be no more than 24 in. (610 mm) o.c.

Ties

• Select ties and spacing appropriate for wall construction and the intended level of connection between the two wythes (non-composite or veneer)

• Use wall ties that distribute lateral loads and accommodate differential movement between wythes

• Use one of the following tie types: unit ties, joint reinforcement, adjustable unit ties, or joint reinforcement with adjustable ties

• Except as noted herein, do not use corrugated ties

• Space ties at a maximum of 32 in. (813 mm) horizontally and 25 in. (635 mm) vertically

• For an air space not exceeding 4⅝ in. (117 mm), provide at least one tie with wire size W1.7 (MW11) per 2.67 sq ft (0.25 m²) of wall area; or at least one tie with wire size W2.8 (MW18) per 3.5 sq ft (0.33 m²) of wall area

• For an air space wider than 4⅝ in. (177 mm) and not exceeding 6⅝ in. (168 mm), provide at least one tie conforming to the requirements of Table 1 per 2.67 sq ft (0.25 m²) of wall area

• For an air space exceeding 6⅝ in. (168 mm), design ties using TMS Code “Alternative design of anchored masonry veneer” provisions

• Provide additional ties within 12 in. (305 mm) of openings larger than 16 in. (406 mm) at a maximum spacing of 3 ft (0.91 m) o.c.

• At columns or other interruptions, install special versions of ties intended for attachment to steel and concrete

Shelf Angles/Lintels

• Provide steel angles conforming to ASTM A36 with a minimum thickness of ¼ in. (6.4 mm)

• Size horizontal leg of shelf angles and lintels to provide minimum bearing of two-thirds the thickness of the brick wythe

• Install continuous flashing above shelf angles and lintels

• Use shelf angles to support veneer exceeding a height of

50 ft (15.24 m)

• Fasten shelf angles to structure using bolts with cast-in inserts, miscellaneous metal fabrications or post-installed anchors

• Where required, provide standoff shelf angle assemblies to allow installation of continuous insulation behind angle

Expansion Joints

• Provide vertical and horizontal expansion joints through brick veneer

• Design and construct expansion joints complying with recommendations of Technical Note 18A

Insulation

• Conduct hygrothermal analysis to determine the optimum type, location and amount of insulation

• Where required, install insulation in one or more of the following locations within the wall assembly: the air space/drainage cavity, the cells of hollow unit backing, or on the interior face of the interior wythe using studs or furring strips

Water Resistive Barriers, Air Barriers and Vapor Retarders

• Conduct hygrothermal analysis to determine suitability and location of air barriers and vapor retarders

• Install sheet, spray or fluid-applied air barrier membrane on exterior face of backing, or detail insulation joints to function as an air barrier

• Installation of sheet, spray or fluid-applied water-resistive barrier membrane preferred but not required

SUMMARY OF RECOMMENDATIONS:

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INTRODUCTION

Drained multi-wythe brick masonry walls were first built in the United States as early as 1850. Their early use was limited primarily to exterior loadbearing walls one or two stories in height. In the 1940s, designers of high-rise buildings began to recognize the advantages of this wall system and used it as an exterior curtain wall element or an infill wall element on buildings with structural frames. Since then, the system has been adopted for both loadbearing and non-loadbearing applications and used extensively throughout the United States in a wide variety of building types. Today, drained multi-wythe brick masonry walls remain popular due to their versatility and the long-term successful performance of the wall assembly.

General Construction Drained multi-wythe brick masonry walls consist of two wythes of masonry separated by an air space and mechanically connected with adjustable ties or horizontal joint reinforcement. As required, the drainage cavity

PROPERTIES OF BRICK VENEER/MASONRY WALLS

Resistance to Moisture Penetration Brick veneer with CMU backing is more resistant to water penetration than barrier wall construction. If moisture penetrates the exterior wythe of masonry, the air space directs it down the back of the exterior brick wythe to the flashing at the bottom of the air space, where it is diverted to the exterior. For further discussion of moisture penetration resistance, refer to the Technical Note 7 Series.

Thermal Properties Both the materials and the construction of the veneer wall assembly contribute to its thermal properties. Brick masonry exhibits significant thermal mass, the ability to store and slowly release heat.

These properties help shift the peak heating or cooling loads to off-peak times and reduce the peak temperatures. Current energy codes accommodate thermal mass by requiring a lower R-value for mass walls. Refer to the Technical Note 4 Series for more information.

The separation of the exterior and interior wythes by the air space reduces clear field thermal bridging and reduces the rate at which heat moves through the wall assembly. Insulation may be placed in the air space by attaching or spraying continuous insulation on the backing, or it may be placed in the masonry cores of the backing by filling them with granular fill or foam. Insulation may also be placed on the interior face of the backing, where it is typically placed between furring strips supporting gypsum wallboard interior finishes.

Fire Resistance Fire resistance ratings of brick veneer walls with CMU backing range from 2 to 4 hours, depending upon the wall thickness and other factors. The fire rating of various types of brick wall assemblies with CMU backing can be calculated using the formulas in Technical Note 16. The inclusion of plastic-based materials (such as drainage board, insulation and mortar dropping collection devices) within the air space may increase the risk of fire spread within the wall assembly. To evaluate this condition, the IBC requires NFPA 285 testing to be conducted on such wall assemblies to determine the potential for fire propagation. Certain brick and CMU wall assemblies that have a maximum clearance between the brick and the insulation of 1 in. (25.4 mm) qualify for an exception in the IBC and do not require NFPA 285 testing.

Sound Transmission Sound on one side of a wall assembly can cause vibration of the closest masonry wythe. In a multi-wythe masonry wall, the air space provides a partial isolation of the two wythes, which creates a cushioning effect. This cushioning effect, combined with the mass of the masonry, dampens and greatly reduces the vibration caused by the sound source.

For instance, a wall with a 4 in. (250 mm) thick brick veneer and a hollow 8 in. (203 mm) thick CMU backing has a Sound Transmission Class (STC) rating of 53, which is usually sufficient for substantially reducing transfer of typical interior and exterior noises. Similar values can be achieved for Outside-Inside Transmission Class (OITC) ratings.

For more information on sound transmission, see Technical Note 5A.

www.gobrick.com | Brick Industry Association | TN 28D | Brick Veneer/Concrete Masonry Walls | Page 3 of 19 may also include continuous insulation and an air/ moisture/vapor barrier. When a drained multi-wythe brick masonry wall encloses occupied space, furring members and gypsum wallboard are typically installed on the interior face of the interior wythe. Placement of insulation in the wall assembly may vary and can include insulation in the air space, insulation within the cells of hollow masonry units or insulation inboard of the interior wythe, as well as various combinations of these locations.

Various materials can be used in a multi-wythe masonry wall. The exterior wythe generally consists of solid or hollow brick but can also include architectural concrete masonry units (CMU), calcium silicate units or cast stone accents. The interior wythe can consist of large-scale hollow brick, structural clay tile or CMU.

An example using a solid brick exterior wythe and a CMU interior wythe is depicted in Figure 1.

Structural Performance The various configurations and uses of multi-wythe masonry demonstrate the versatility of this wall assembly. A multi-wythe masonry wall can be either loadbearing or non-loadbearing, and within those categories it can consist of composite, non-composite or veneer construction. These categories are described in more detail as follows:

Loadbearing vs. Non-Loadbearing. A loadbearing wall is defined by its role as a primary element in the structural system of the building. It carries both gravity load (dead load, live load) and lateral load (forces from wind and earthquake). A non-loadbearing wall is a secondary element in the structural system. It does not carry gravity load, other than its self-weight, but resists lateral load and transfers it to the structural frame of the building.

Composite, Non-Composite and Veneer. These terms describe how the wall assembly resists the loads applied to it. In a composite wall, both wythes work together as a single element, resisting both lateral and vertical loads. The ties must meet specific requirements for size and spacing in order to connect the two wythes such that composite behavior is achieved. A non-composite wall is similar; however, each wythe resists a proportion of the load individually based on its stiffness. The ties connecting the non-composite wythes permit loads to be transferred among wythes, but the ties are not sufficient to create shared load resistance by the combined section.

In veneer walls, the exterior wythe (veneer) does not resist any load other than its self-weight and only transfers lateral load to the backing, which resists the full load.

Anchored Veneer vs. Cavity Wall. Nearly all multi-wythe masonry walls constructed today consist of an exterior wythe categorized as an anchored veneer. Another category of multi-wythe masonry is a cavity wall, which is less prevalent today. As defined by TMS 402, Building Code Requirements for Masonry Structures (TMS Code) [Ref. 2] and TMS 602, Specification for Masonry Structures (TMS Specification) [Ref. 10], a cavity wall is a non-composite masonry assembly with a continuous air space separating at least two wythes and with ties connecting each wythe. However, many design and construction professionals refer to any brick veneer drained wall assembly as a cavity wall. Be sure to clarify terminology to avoid confusion.

This Technical Note will focus primarily on anchored brick veneer with a backing of concrete masonry because it is the most common combination for contemporary drained multi-wythe wall assemblies. For simplicity, this type of wall will be referred to as brick veneer/CMU (BV/CMU).

Building Science Performance Modern building construction has increased energy efficiency, in part by incorporating materials and methods that were not used historically. Materials such as plastic-based insulation, air barriers and vapor retarders are regularly installed within wall assemblies, but they have a wide range of properties with respect to permitting or impeding the movement of moisture and air, as well as resisting or propagating fire.

Figure 1 Typical Brick Veneer/CMU Wall www.gobrick.com | Brick Industry Association | TN 28D | Brick Veneer/Concrete Masonry Walls | Page 4 of 19

While these materials help to improve performance, they must be used correctly to avoid unintended consequences. Differences in temperature and humidity between the interior and exterior of a building mean that moisture from the air may condense within the wall assembly. The goal is to control where condensation will occur through proper material selection and placement, and to create a location within the wall assembly that can manage the moisture and direct it to the exterior. In the case of a brick veneer wall assembly, the ideal location is the drainage cavity/air space.

Hygrothermal analysis, which models the heat and moisture flow through a wall assembly, can be used to determine points in the wall where condensation may occur. This modeling can also compare similar wall assemblies with different component materials, component placement and insulation thicknesses to determine the configuration best suited to the local climate and the code requirements for the project.

Specific to brick veneer wall assemblies, widening the air space to increase the drying potential of the wall and including continuous insulation in the drainage cavity to supplement the insulating function of the air space are effective strategies to force condensation to occur within the “wet zone” of the wall assembly. For further discussion on causes and prevention of condensation within brick veneer wall assemblies, refer to Technical Note 47.

DESIGN OF BV/CMU WALLS

The following describes the various components of the BV/CMU wall system in more detail, with commentary about the appropriate materials and their function.

Brick Solid brick units must meet the requirements of ASTM C216, Standard Specification for Facing Brick, or ASTM C62, Standard Specification for Building Brick [Ref. 1]. Hollow brick units must meet the requirements of ASTM C652, Standard Specification for Hollow Brick. Grade SW brick is the default for brick conforming to ASTM C216, C62 and C652 and is recommended for use in most areas of the United States. Note that brick meeting ASTM C62 are not subject to appearance requirements. Grade MW brick can be used for interior wythes in these areas, but the limited availability and potential for construction errors may outweigh the benefit of its use.

Single-fired ceramic glazed brick used for either the exterior or interior wythe of BV/CMU walls must meet the requirements of ASTM C1405, Standard Specification for Glazed Brick (Single Fired, Brick Units). Other ceramic glazed units may conform to ASTM C126, Standard Specification for Ceramic Glazed Clay Facing Tile, Facing Brick and Solid Masonry Units, or other appropriate standards.

Information on the classification and selection of brick can be found in Technical Notes 9A and 9B, respectively.

Further information on brick masonry material selection for adequate strength and compliance with the TMS Code and Specification can be found in the Technical Note 3 Series.

Other Masonry Units CMU. As indicated in the “General Construction” section of this Technical Note, CMU are usually installed as the backing material for exterior brick veneer. CMU with an architectural finish may also be used as accent bands in the exterior brick wythe. Solid and hollow concrete masonry units must conform to ASTM C90, Standard Specification for Loadbearing Concrete Masonry Units, or ASTM C1634, Standard Specification for Concrete Facing Brick, respectively.

Structural Clay Tile. Structural clay tile may also be used as the interior wythe of multi-wythe masonry wall construction. Structural clay tile used for this purpose must conform to ASTM C34, Standard Specification for Structural Clay Loadbearing Wall Tile, or ASTM C212, Standard Specification for Structural Clay Facing Tile.

Where structural clay tile are glazed, they must also conform to ASTM C126, Standard Specification for Ceramic Glazed Structural Clay Facing Tile, Facing Brick, and Solid Masonry Units. Clay tile conforming to ASTM C212 and C126 are sometimes used for the interior wythe of a multi-wythe masonry wall when left exposed for their architectural appearance.

Cast Stone. Cast stone is a specialty architectural concrete product fabricated to replicate natural cut building stone, such as limestone. As such, cast stone units are frequently used within brick facades as sills, fenestration surrounds, keystones, copings, water tables, and other trim or accent elements. Cast stone must conform to www.gobrick.com | Brick Industry Association | TN 28D | Brick Veneer/Concrete Masonry Walls | Page 5 of 19

ASTM C1364, Standard Specification for Architectural Cast Stone, and the Standards for Architectural Cast Stone (TMS 404, 504 and 604) [Ref. 12], which cover the design, fabrication and installation of cast stone.

Calcium Silicate Units. Calcium silicate masonry is a non-cementitious manufactured stone product that is formed using pressure and cured in an autoclave. It is used similarly to cast stone as an accent element in an exterior brick facade. Calcium silicate units must conform to ASTM C73, Standard Specification for Calcium Silicate Brick (Sand-Lime Brick).

Mortar Masonry mortar must conform to the requirements of ASTM C270, Standard Specification for Mortar for Unit Masonry. This standard includes a proportion-based specification and a property-based specification for each mortar Type; the proportion-based option is the default and is most commonly specified. Type N or S mortars are typically used in brick masonry veneer walls, with Type N preferred in veneer or non-loadbearing applications and Type S preferred in loadbearing applications. Mortars with air content of less than 12 percent are recommended for their bond strength and resistance to moisture penetration.

Portland cement-lime, mortar cement or masonry cement mortars can be used. While all three mortar Types meet specifications, they are not equal and must be evaluated for project-specific compatibility. The TMS Code requires reduced allowable flexural tensile stresses for assemblies constructed with masonry cement mortars or air-entrained portland cement-lime mortars. In addition, the TMS Code prohibits the use of all Type N mortars in Seismic Performance Categories D and E and permits the use of masonry cement mortars only if the masonry elements are fully grouted.

See the Technical Note 8 Series for more detailed information on mortar Types and selection, and Technical Note 7A for a discussion of brick and mortar compatibility.

Drainage Cavity/Air Space The drainage cavity or air space between wythes is permitted to vary from 1 to 6⅝ in. (25.4 to 168 mm), per the prescriptive requirements of the TMS Code. Although permitted, air spaces less than 2 in. (50 mm) are not recommended. Where the exterior wythe acts as a veneer, the prescriptive requirements of the TMS Code permit the air space to be a maximum of 6⅝ in. (168 mm) wide. Where the exterior wythe acts as a part of a non-composite wall, the prescriptive requirements are for an air space no wider than 4½ in. (114 mm).

In many climate zones, the optimum location to place continuous insulation in the wall assembly is the air space.

When insulation is placed in the air space, the clearance from the interior of the brick to the exterior side of the insulation must be no less than a nominal 1 in. (25.4 mm). This provides sufficient space for the mason to lay the brick properly and for the wall to function as a drainage wall.

For air spaces between 4⅝ and 6⅝ in. (117 and 168 mm), more substantially sized ties are required. Air spaces greater than 6⅝ in. (168 mm) may adversely impact the ability of typical masonry ties applied at the code-prescribed spacing to properly transfer lateral loads. Where these larger air spaces are used, supplemental and/ or stronger ties are generally necessary to achieve adequate load transfer capability, which requires additional product research and engineering analysis.

Insulation Properties of insulation materials vary widely. Due to the large number of types of insulation, and the even larger number of manufacturers, individual manufacturers must be consulted for design values and other properties of their specific materials and their applications. Manufacturers’ literature should be reviewed in detail before selection. In general, plastic insulation placed within a wall assembly requires testing to determine its potential to contribute to fire spread per NFPA 285 [Ref. 8]. However, the International Building Code (IBC) [Ref. 5] does not require this testing when the plastic insulation is covered on each face by 1 in. (25.4 mm) or more of masonry or concrete, the air space is limited to 1 in. (25.4 mm), and the plastic insulation has a Class A flame spread rating.

If needed, many manufacturers of insulation installed in masonry wall assemblies have results for NFPA 285 available for review.

Refer to the Technical Note 4 Series for more information on energy and insulation of brick masonry walls and to Technical Note 47 for information on prevention and control of condensation.

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Placement. There are multiple options for insulation placement within a BV/CMU assembly. Insulation can be placed 1) in the drainage cavity/air space; 2) in the cells of hollow unit backing; or 3) on the interior face of the interior wythe between studs or furring strips. The optimum location and amount of insulation needed for a particular building can be obtained from hygrothermal analysis. In recent years, the thickness of insulation required within the drainage cavity has increased in many climate zones. The use of standoff shelf angles permits insulation installed in the drainage cavity to continue behind the vertical leg of the angle, which reduces the thermal bridging effect caused by the shelf angle. When insulation is installed in the drainage cavity/air space, it is critical that the product be intended for use in the “wet zone” of a wall assembly and have an established history of successful use in this application. Insulation applied to the drainage cavity side of the interior wythe can sometimes form part of the air barrier system. For insulation to work effectively as an air barrier, proper attachment to the interior masonry wythe and fully sealed or taped joints are necessary.

Board Insulation. Many board insulation materials can be installed in the air space of BV/CMU walls. Among the most common are rigid plastic foams: expanded polystyrene (EPS), extruded polystyrene (XPS) and polyisocyanurate. Mineral wool is considered semi-rigid and is included within this category, as it is typically installed in similar-sized sheets and locations as rigid board insulation. Although similar in appearance to fiberglass batt insulation, mineral wool is fire-resistant and does not absorb moisture, resisting rot and biological growth while maintaining its R-value. Insulation boards are attached to the interior face of the drainage cavity using insulation adhesive or mechanical fasteners, which can include clips or plates that slip over the veneer ties.

A minimum clearance of a nominal 1 in. (25.4 mm) must be maintained between the face of the insulation and the back of the brick.

Rigid board insulation must conform to one of the following material standards: ASTM C578, Standard Specification for Rigid, Cellular Polystyrene Thermal Insulation; ASTM C1224, Standard Specification for Reflective Insulation for Building Applications; or ASTM C1289, Standard Specification for Faced Rigid Cellular Polyisocyanurate Thermal Insulation Board. Mineral wool insulation for use in BV/CMU walls must conform to ASTM C612, Standard Specification for Mineral Fiber Block and Board Thermal Insulation.

There are also proprietary formed rigid foam inserts that can be used as integral insulation placed inside the cells of hollow CMU to improve thermal and sound transmission performance. These products are generally made from EPS foam.

Granular Fills. Granular fills are typically used in the hollow cells of concrete block backing. One advantage of granular fills is that they can be installed after wall sections have been completed. This permits the mason to work uninterrupted, shortening construction time and lowering costs. However, the water resistance of the fill is of utmost importance. Settling of the fill material may lead to thermal bridging in the wall system. Two types of granular fill may be used for BV/CMU insulation: water-repellent vermiculite and silicone-treated perlite insulation.

EPS bead granular fill is not recommended.

Vermiculite is an inert, lightweight material manufactured by expanding an aluminum magnesium silicate mineral, which is a form of mica, to 15 times its original size by subjecting it to high temperatures. Perlite is a white, inert, lightweight material made from crushed volcanic siliceous rock. Exposure to high temperature creates a void structure within the rock, and further heating can expand perlite to 20 times its original volume. Water-repellent vermiculite and silicone-treated perlite must conform to ASTM C516, Standard Specification for Vermiculite Loose Fill Thermal Insulation, and ASTM C549, Standard Specification for Perlite Loose Fill Insulation, respectively. Each of these specifications contains limits on density, grading, thermal conductivity and water repellency.

Installation of granular fill is relatively straightforward. Bags of material are placed into the top of the open cells, either directly or via hoppers. A 20 ft height limit for a placement lift is recommended to ensure that the cells are fully filled without gaps. To maintain the thermal performance, do not rod or tamp the fill.

Foamed-in-Place. Foamed-in-place insulation has traditionally been used to fill the cells of hollow masonry units. These foams may consist of cementitious material (magnesium oxychloride cement and ceramic talc) or aminoplast resin. One advantage of foamed-in-place insulation is that it can be installed after wall sections have been completed, which is beneficial for filling cells of hollow masonry. The insulation is placed under pressure through ports in the side of the wall. Newly constructed walls must be allowed to cure long enough to resist the pressures applied. Foamed-in-place insulation does not have an ASTM material standard, but the performance properties of the material are determined using relevant ASTM test standards.

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Spray Polyurethane Foam. Spray foam insulation can be applied directly to the outer face of the interior wythe of a BV/CMU wall and can serve as a water-resistive barrier and an air barrier. When used in the drainage cavity or on the interior face of a wall, spray foam insulation is typically applied before the exterior brick wythe or interior finishes are installed. Polyurethane spray foam must comply with ASTM C1029, Standard Specification for Spray Applied Rigid Cellular Polyurethane Thermal Insulation.

One disadvantage of spray foam is that shrinkage of the foam may occur. This condition could lead to moisture drainage paths and air leakage through the wall system; therefore, compatible membranes are installed at edges and transitions on the interior wythe to ensure coverage of the underlying substrate when shrinkage occurs.

Most foams are multicomponent systems formed by a chemical reaction of two or more liquids that expand when combined and require specialized equipment to install. The insulation materials that fall within the categories of foamed-in-place and spray foam have different properties and characteristics, such as open cell vs. closed cell, resistance to moisture and R-values. As such, some foams may be better suited to filling cells in hollow masonry than filling the drainage cavity/air space. Manufacturers’ literature should be consulted for technical information on applications and usage.

Air Barriers, Water-Resistive Barriers and Vapor Permeance As discussed in the previous section, insulation can be placed in the drainage cavity/air space, in the cells of hollow unit backing or on the interior face of the interior masonry wythe. The placement of the insulation plays a role in determining where the air barrier and vapor retarder should be installed within the wall assembly. The results of the hygrothermal analysis can help determine the placement of the air barrier and vapor retarder.

Air Barriers. Controlling airflow within the wall assembly helps to eliminate drafts and prevents moisture-laden air from reaching areas of the wall assembly intended to remain dry. As a result, building codes require air barriers.

Per the International Energy Conservation Code (IECC) [Ref. 6], an air barrier consists of “one or more materials joined together in a continuous manner to restrict or prevent the passage of air through the building envelope and its assemblies.” Masonry walls with CMU backing can appear relatively airtight but may experience air leakage when a dedicated air barrier product is not used. The use of block filler or two layers of paint allow a CMU wall to comply as an approved air barrier assembly. Some air barrier materials such as membranes or insulation can also perform as water-resistive barriers.

Water-Resistive Barriers. Water-resistive barriers (WRB) are intended to resist liquid water that has penetrated behind the exterior wythe from further intruding into the wall assembly. The use of a WRB is not required by building codes for wall assemblies with masonry or concrete backup construction, but a WRB is sometimes installed on the exterior face of the interior wythe to protect against ingress of incidental moisture or moisture-laden air that reaches that interface. If applied, the WRB must be continuous over the backing and must be sealed at interfaces with other elements or materials.

Parging. Historically, parging the exterior or interior face of the interior masonry wythe with mortar was used to reduce air and water leakage. However, the effectiveness of parging is limited due to the tendency of cementitious materials to crack and because it is not recognized by the building code to serve as a water-resistive barrier.

Parging qualifies as an air barrier assembly per the IECC, provided that it is portland cement based and has a minimum ½ in. (13 mm) thickness. In some cases, parging may be recommended for application as a substrate for another air barrier or water-resistive barrier membrane; however, the manufacturers of air barrier and water-resistive barrier membranes typically have their own surface preparation requirements that may or may not be compatible with the use of parging.

Vapor Permeance. A material’s vapor permeance controls the amount of moisture that can be transmitted through it (vapor diffusion). Materials with a higher vapor permeance/permeability are often referred to as “breathable.” Both air barriers and water-resistive barriers can have various levels of permeability; the suitability of a particular product depends on the code requirements for a vapor retarder in the wall assembly and the results of the hygrothermal analysis.

In-depth discussion of air barriers, water-resistive barriers and vapor retarders is outside the scope of this Technical Note. There are many building science resources available for reference [see Ref. 3]. For buildings with unusual walls, consultation with building envelope professionals is recommended for development of project-specific recommendations for materials and placement of those materials in the wall assembly. For further discussion on air barriers, water-resistive barriers and vapor retarders, refer to the Technical Note 7 Series.

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Wall Ties/Anchors For the purposes of this Technical Note, the term “tie” is used to describe a fastener connecting the veneer to the backing or an outer wythe to an inner wythe. The TMS Code uses the term “anchors” to describe the fasteners that attach the brick veneer to the structural backing. In the context of composite or non-composite walls, the term “anchors” sometimes refers to fasteners used to connect the inner wythe of the wall to the structure, and the term “ties” refers to the fasteners used to connect the separate wythes of masonry.

For a tie system to function properly, it must meet the following criteria:

• Be securely attached to or embedded in the masonry wythes

• Have sufficient strength to transfer lateral loads with minimal deformations

• Have a minimal amount of mechanical play (if adjustable)

• Have sufficient corrosion resistance

• Be easily installed without damage to the tie system or other wall components

Connection to Frame. Masonry walls used to enclose or infill frame structures must be carefully designed and detailed to permit the transfer of loads applied to the wythes to the frame in a manner that accommodates differential movement. The anchorage of the exterior veneer to the building frame generally provides out-of-plane support for the veneer and resists tension and compression from the loads perpendicular to the plane of the wall.

This permits in-plane differential movement between the building frame and the exterior veneer without causing distress. Ties must be designed and detailed to accommodate construction tolerance differences and differential movement resulting from loads applied to the frame and floor elements. Horizontal joint reinforcement and separate ties should not be placed in the same bed joint, as there is not adequate space to accommodate both and surround them with mortar.

Connection of Wythes. Ties serve three important functions: to provide a connection for each wythe, to transfer lateral loads between wythes and to accommodate differential movement between wythes. There are multiple tie types for use in brick veneer walls with CMU backing, including unit ties, horizontal joint reinforcement and adjustable ties. All types must conform to the applicable requirements for wire size, tie spacing and configuration listed in the TMS Code and summarized in Table 1 and Table 2.

TABLE 1

Adjustable Tie Requirements for Brick Veneer with a Backing of CMU or Concrete¹

Air Space,

in. (mm) Tie Type Minimum

Wire Size

Maximum Wall Area per Tie, sq ft (m²)

Backing Attachment Requirements

Pintle or Adjustable Part Requirements

≤ 4⅝ (117)

Joint Reinforcement with

Adjustable Ties or

Adjustable Unit Ties²

W1.7

(MW11) 2.67 (0.25)

Ladder, Tab or Eye:

Min. wire W1.7 (MW11) Plate:

Min. 0.06 in. (1.5 mm) thick and ⅞ in. (22.2 mm) wide

Wire:

Min. W2.8 (MW18) Pintle Legs:

1 min.

Offset:

Max. 1¼ in. (31.8 mm)

> 4⅝ (117) and

≤ 6⅝ (168)

Joint Reinforcement with

Adjustable Ties or

Adjustable Unit Ties²

W2.8

(MW18) 2.67 (0.25)

Ladder, Tab or Two Eyes:

Min. wire W2.8 (MW18) Barrel:

Min. ¼ in. (6.4 mm) outside dia.

Plate/Prong:

Min. 0.074 in. (1.88 mm) thick and 1¼ in. (31.8 mm) wide

Wire:

Min. W2.8 (MW18) Pintle Legs:

2 min.

Offset:

Max. 1¼ in. (31.8 mm) Distance from Inside Face of Brick to End of Adj. Part:

Max. 2 in. (51 mm)

> 6⅝ (168) Design ties using TMS Code “Alternative design of anchored masonry veneer” provisions

1. Tie requirements shown are for brick veneer with a backing of CMU or concrete, as appropriate. For multi-wythe masonry with composite or non-composite action, see the TMS Code for tie requirements.

2. Adjustable unit ties may also include a sheet-metal adjustable part (dovetail anchors). Sheet-metal adjustable parts should conform to backing attachment requirements for plate in air spaces less than or equal to 4⅝ in.

www.gobrick.com | Brick Industry Association | TN 28D | Brick Veneer/Concrete Masonry Walls | Page 9 of 19

TABLE 2

Non-Adjustable Tie Requirements for Brick Veneer with a Backing of CMU or Concrete¹

Air Space,

in. (mm) Tie Type² Minimum Wire or Plate Size Maximum Wall Area per Tie, sq ft (m²)

≤ 4⅝ (117)

Joint Reinforcement and Unit Ties—Wire

W1.7 (MW11) 2.67 (0.25)

W2.8 (MW18) 3.50 (0.33)

Unit Ties—Sheet-Metal Min. 0.06 in. (1.5 mm) thick and ⅞ in. (22.2 mm) wide 3.50 (0.33)

> 4⅝ (117) and ≤ 6⅝ (168) Joint Reinforcement W2.8 (MW18) (longitudinal and cross wires) 1.77 (0.16)³

> 6⅝ (168) Design ties using TMS Code “Alternative design of anchored masonry veneer” provisions

1. Tie requirements shown are for brick veneer with a backing of CMU or concrete, as appropriate. For multi-wythe masonry with composite or non-composite action, see the TMS Code for tie requirements.

2. It is recommended that unit ties in air spaces greater than 4⅝ in. should be designed using TMS Code “Alternative design of anchored masonry veneer” provisions.

3. Recommended maximum wall area per tie. Assumes placement of joint reinforcement at 16 in. o.c. vertically (two courses of typical

CMU).

Note that as the air space dimension increases, the requirements for ties become more stringent.

Additional ties must be provided within 12 in.

(305 mm) of openings larger than 16 in. (406 mm) at a maximum spacing of 3 ft (0.91 m) o.c. It is recommended to place ties within 12 in. (305 mm) of veneer expansion joints and edges of veneer.

Unit Ties/Anchors. Unit ties can be formed from wire or sheet-metal. Typical wire ties are rectangular ties or “Z” ties, as shown in Figure 2. Metal “Z” ties are intended to be used between wythes of solid masonry units only and are not appropriate for hollow masonry units. Rectangular ties can be used between the wythes of all masonry units, including solid and hollow units, and are therefore recommended for multi-wythe, non-composite masonry walls. Wire ties should be of wire size W1.7 (0.148 in. [3.8 mm]) or W2.8 (3⁄16 in.

[4.8 mm]) in diameter. Sheet-metal ties must have a minimum base metal thickness of 0.06 in. (1.5 mm) or 16 gage.

Joint Reinforcement. Horizontal joint reinforcement configurations available are the ladder, truss and tab types shown in Figure 3. When used to tie the inner and outer wythes together, the interior and exterior wythes each receive at least one longitudinal wire.

The longitudinal wires are connected by cross wires to tie the wythes together. Horizontal joint reinforcement is typically produced in 10 to 12 ft (3 to 4 m) lengths.

Longitudinal wires are typically wire size W1.7 or W2.8 in diameter. Cross wires are also W1.7 or W2.8 in diameter and should be spaced at a maximum of 16 in. (406 mm) o.c. horizontally. The total thickness of the wires must not exceed one-half the mortar joint thickness.

Tests indicate that BV/CMU walls tied with horizontal joint reinforcement have similar performance to those

Figure 2 Unit Ties

Figure 3 Joint Reinforcement

Ladder Type

3-Wire Ladder Type

Truss Type

3-Wire Truss Type

Tab Type

Rectangular Tie “Z” Tie www.gobrick.com | Brick Industry Association | TN 28D | Brick Veneer/Concrete Masonry Walls | Page 10 of 19 tied with metal unit ties. These tests also indicate that truss type joint reinforcement used in BV/CMU wall construction helps to develop a degree of composite action in the horizontal span but does not contribute to any composite action in the vertical span. This restraint in the horizontal direction will reduce the amount of in-plane movement and could possibly result in bowing of the masonry walls. In addition, if the inner wythe consists of reinforced masonry, the diagonal cross wires of truss type joint reinforcement can conflict with the vertical reinforcing bars and the placement of grout in those cells.

Therefore, truss type joint reinforcement is not recommended for BV/CMU walls. Instead, ladder type and tab type joint reinforcement, which allow for the in-plane movement between the wythes, are recommended.

Adjustable Unit Ties/Anchors. Adjustable unit ties typically consist of two pieces in a double eye and pintle configuration, shown in Figure 4. The piece with the eyes is installed during construction of the inner wythe, while the piece with the pintle(s) is installed during construction of the exterior wythe. Adjustable pintle ties are required to have a minimum wire size of W2.8 in diameter and a maximum vertical offset between the eye and pintle components of 1¼ in. (31.8 mm).

In addition, adjustable ties should be detailed to prevent disengagement and have a maximum horizontal out-of-plane mechanical play within the connecting pieces of 1⁄16 in.

(1.6 mm).

Joint Reinforcement with Adjustable Ties/Anchors. Joint reinforcement with adjustable ties in a ladder and truss type configuration are also available, as shown in Figure 5. This type of tie consists of rectangular tie extensions with eyes connected to standard joint reinforcement. The use of the combined joint reinforcement and adjustable ties is preferred for brick veneer walls with CMU backing, as it avoids potential conflicts between unit tie wires and joint reinforcing wires.

Masonry Headers. Contemporary multi-wythe masonry walls are typically bonded by the use of metal ties;

however, masonry headers may be encountered in older wall construction. A header is a masonry unit laid perpendicular to the exterior wythe, or sometimes at an angle to the exterior wythe, that is used to connect two wythes of masonry. The TMS Code still permits the use of masonry headers and includes provisions for the evaluation of their shear capacity, embedment and minimum percentage within the wall. Although the TMS Code allows wythes of masonry designed for composite action to be bonded structurally by masonry headers, they are not commonly used in contemporary construction. The use of masonry headers is no longer recommended due to their lack of ductility, limited ability to accommodate differential movement, and because they provide a direct path for water penetration from the outside of the wall to the interior along the head and bed joints.

Workmanship. Construction workmanship is critical to achieving high-performing masonry. While design, detailing and material selection is important, good workmanship cannot be overemphasized. Therefore, all mortar joints in both the exterior and interior masonry wythe should be completely filled as the brick—and CMU, if applicable—are laid. Face shell bedding of CMU is permitted. All mortar joints must be tooled or struck in a profile to consolidate the mortar at the surface of the brick masonry, which protects against water penetration. Technical Note 7B discusses more information related to workmanship issues for brick masonry. One workmanship consideration specific to BV/CMU construction is that both wythes of masonry must be adequately and properly tied together.

The main concern for the designer is assurance that all the ties are firmly embedded in and bonded to the mortar. To achieve this, the masonry wythes must be laid with completely filled bed joints, and the ties must be spaced properly with a minimum ⅝ in. (16 mm) of mortar cover from the exterior face of the brick and a minimum embedment of 1½ in. (38.1 mm). Extensive data indicates that wall ties have excellent tying capacity when they

Figure 4 Adjustable Unit Ties

Figure 5 Joint Reinforcement with Adjustable Ties

Ladder Types

Truss Types www.gobrick.com | Brick Industry Association | TN 28D | Brick Veneer/Concrete Masonry Walls | Page 11 of 19 are fully embedded in the masonry bed joints. If any ties are improperly embedded in the masonry units, the ties that are installed correctly will be required to carry the load of those that are not, resulting in potential overloading of ties and a weak structural system for the wall assembly as a whole.

Further discussion on proper tie selection and other applicable code requirements for veneer ties used with concrete or CMU backing is discussed in Technical Note 44B.

Shelf Angles/Lintels Lintels provide support of brickwork over masonry openings by bearing on the brickwork on each side of the opening.

They are not attached to the building structure. Shelf angles provide continuous intermediate support for the brickwork through connection to the building structure. Shelf angles are occasionally referred to as relieving angles.

Brick veneer walls with a rigid backing of concrete or CMU have no prescriptive height limitations in the TMS Code and therefore do not require the use of shelf angles. However, the maximum recommended height that brick veneer with this rigid backing may be supported at the foundation and between shelf angles is approximately 50 ft (15 m).

Shelf angles and lintels are designed similarly, except that a shelf angle must carry the full weight of brick masonry above, while a lintel is typically permitted to carry a reduced load due to the arching action of the wythe supported. Steel angles are most frequently used as shelf angles and lintels, but lintels may also be reinforced masonry, precast concrete or stone. Steel used for shelf angles and lintels must conform to the requirements in ASTM A36/A36M, Standard Specification for Carbon Structural Steel. All non-galvanized steel and non-stainless steel angles should be primed and painted (with a commercial or industrial corrosion-inhibiting coating) to prevent corrosion. In harsher climate conditions, consider the use of hot-dipped galvanized or stainless-steel angles.

Steel angles should have a minimum thickness of ¼ in. (6.4 mm). The horizontal leg of the shelf angle or lintel must be sized to accommodate a dimension of two-thirds the thickness of the brick veneer at a minimum. The maximum allowable deflection along the length of the shelf angle or lintel is L/600, and the total rotation of the toe of the shelf angle is limited to 1⁄16 in. (1.6 mm). Lintels require a minimum bearing length of 4 in. (102 mm) on the brick at each side of the opening. Shelf angles should not be installed as one continuous member. Space should be provided at intervals to permit thermal expansion and contraction of the steel angle without causing cracking or other distress of the masonry.

For concrete structures, shelf angles are typically fastened using bolts corresponding to a matching wedge insert cast into the concrete. Alternatively, cast-in embed plates may be present on concrete structures, which permit welding as an attachment method. For steel structures, miscellaneous metal fabrications are used. Post-installed anchors designed for structural anchorage into cured concrete, grouted masonry and hollow masonry can also be used to connect shelf angles to the structure. The structural engineer for the project must design these fabrications and connections. Standoff shelf angles can be designed by the structural engineer, by fabricating miscellaneous metal brackets or by using prefabricated standoff shelf angle brackets. Prefabricated brackets may be either fully proprietary systems including brackets and the brick support or brackets intended for use with standard hot-rolled angle shapes. Where shims are installed between the shelf angle and the structure, the shims must extend the full height of the vertical leg of the angle to ensure that load transfer is consistent with the design.

For further information on the design of lintels and shelf angles, refer to Technical Note 31B.

Through-Wall Flashing Through-wall flashing is an impervious material installed in a drainage wall system to contain and redirect moisture that has penetrated back to the exterior. Similar to other drainage wall assemblies, flashing is required at the base of the wall, above and below all wall openings, at shelf angles, at the tops of walls, beneath copings, and at any other discontinuities in the air space. Flashing should extend to the face of the exterior brick wythe at a minimum. However, extending the flashing beyond the face of the brick and forming a drip promotes improved drainage, which is preferred. Where flashing is not continuous, the ends of the flashing should be turned up a minimum of 1 in. (25 mm) to form an end dam.

Aspects of flashing unique to brick veneer with concrete or CMU backing include the following:

• The vertical leg of the flashing should extend up the backing a minimum of 8 in. (203 mm) and be terminated in a bed joint of the interior masonry wythe or a horizontal slot (reglet) in concrete. If www.gobrick.com | Brick Industry Association | TN 28D | Brick Veneer/Concrete Masonry Walls | Page 12 of 19 desired, flashing can be mounted to the face of the backing using a termination clamp or bar with fasteners intended for masonry or concrete applications.

• In some locations, the inner wythe of the BV/CMU wall is not…