A wall constructed with two or more wythes of masonry can technically be classified in one of three ways, depending on how each individual wythe is designed and detailed. These three wall systems are composite, noncomposite or veneer walls. A true veneer is nonstructural—any contribution of the veneer to the wall’s out-of plane load resistance is neglected.
Building Code Requirements for Masonry Structures (ref. 1) defines veneer as a masonry wythe which provides the exterior finish of a wall system and transfers out-of-plane loads directly to the backing, but is not considered to add load resisting capacity to the wall system.
Noncomposite walls, on the other hand, are designed such that each wythe individually resists the loads imposed on it. Bending moments (flexure) due to wind or gravity loads are distributed to each wythe in proportion to its relative stiffness.
Composite walls are designed so that the wythes act together as a single member to resist structural loads. This requires that the two masonry wythes be connected by masonry headers or by a mortar or grout filled collar joint and wall ties to help ensure adequate load transfer between the two wythes.
The primary function of anchored veneers is to provide an architectural facade and to prevent water penetration into the building. As such, the structural properties of veneers are neglected in veneer design. The veneer is assumed to transfer out-of-plane loads through the anchors to the backup system. Building Code Requirements for Masonry Structures Chapter 6 (ref. 1) includes requirements for design and detailing anchored masonry veneer.
A masonry veneer with masonry backup and an air space between the masonry wythes is commonly referred to as a cavity wall. The continuous air space, or cavity, provides the wall with excellent resistance to moisture penetration and wind driven rain as well as a convenient location for insulation. This TEK addresses concrete masonry veneer with concrete masonry backup.
DESIGN CONSIDERATIONS
Masonry veneers are typically composed of architectural units such as: concrete or clay facing brick; split, fluted, glazed, ground face or scored block; or stone veneer. Most commonly, anchored masonry veneers have a nominal thickness of 4 in. (102 mm), although 3 in. (76 mm) veneer units may be available as well.
Although structural requirements for veneers are minimal, the following design considerations should be accounted for: crack control in the veneer, including deflection of the backup and any horizontal supports; adequate anchor strength to transfer applied loads; differential movement between the veneer and backup; and water penetration resistance.
The continuous airspace behind the veneer, along with flashing and weeps, must be detailed to collect any moisture that may penetrate the veneer and direct it to the outside. A minimum 1 in. (25 mm) air space between wythes is required (ref. 1), and is considered appropriate if special precautions are taken to keep the air space clean (such as by beveling the mortar bed away from the cavity or by placing a board in the cavity to catch and remove mortar droppings and fins while they are still plastic). Otherwise, a 2 in. (51 mm) air space is preferred. As an alternative, proprietary insulating drainage products can be used.
Although veneer crack control measures are similar to those for other concrete masonry wall constructions, specific crack control recommendations have been developed for concrete masonry veneers. These include: locating control joints to achieve a maximum panel length to height ratio of 11/2 and a maximum spacing of 20 ft (6,100 mm), as well as where stress concentrations occur; incorporating joint reinforcement at 16 in. (406 mm) on center; and using Type N mortar for maximum flexibility. See CMU-TEC-009-23, Crack Control Strategies for Concrete Masonry Construction (ref. 2) for more detailed information.
Because the two wythes in a veneer wall are designed to be relatively independent, crack control measures should be employed as required for each wythe. It is generally not necessary for the vertical movement joints in the veneer wythe to exactly align with those in the backup wythe, provided that the ties allow differential in-plane lateral movement.
Wall ties may be joint reinforcement or wire wall ties. Wall ties for veneers transfer lateral loads to the structural wythe and also allow differential inplane movement between wythes. This second feature is particularly important when the two wythes are of materials with different thermal and moisture expansion characteristics (such as concrete masonry and clay brick), or in an insulated cavity wall which tends to have differential thermal movement between the wythes. When horizontal joint reinforcement is used to tie the two wythes together, hot-dipped ladder type reinforcement is preferred over truss type, because the ladder shape accommodates differential in-plane movement and facilitates placing vertical reinforcement, grout and loose fill insulation. Because veneers rely on the backup for support, wall ties must be placed within 12 in. (305 mm) of control joints and wall openings to ensure the free ends of the veneer are adequately supported. More information on ties for veneers can be found in TEK 03-06C, Concrete Masonry Veneers (ref. 4).
The distance between the inside face of the veneer and the outside face of the masonry backup must be a minimum of 1 in. (25 mm) and a maximum of 4 1/2 in. (114 mm). For glazed masonry veneer, because of their impermeable nature, a 2 in. (51 mm) wide airspace is recommended with air vents at the top and bottom of the wall to enhance drainage and help equalize air pressure between the cavity and the exterior of the wall. Vents can also be installed at the top of other masonry veneer walls to provide natural convective air flow within the cavity to facilitate drying. For vented cavities, it is prudent to create baffles in the cavity at the building corners to isolate the cavities from each other. This helps prevent suction being formed in the leeward cavities.
REFERENCES
Building Code Requirements for Masonry Structures, ACI 530-02/ASCE 5-02/TMS 402-02. Reported by the Masonry Standards Joint Committee, 2002.
CMU-TEC-009-23, Crack Control Strategies for Concrete Masonry Construction, Concrete Masonry and Hardscapes Association, 2023.
TEK 03-06C, Concrete Masonry Veneers, Concrete Masonry and Hardscapes Association, 2012.
At critical locations throughout a building, moisture that manages to penetrate a wall is collected and diverted to the outside by means of flashing. The type of flashing and its installation may vary depending upon exposure conditions, opening types, locations and wall types. This TEK includes typical flashing details that have proven effective over a wide geographical range. The reader is also encouraged to review the companion TEK 19-04A Flashing Strategies for Concrete Masonry Walls (ref. 1) which addresses the effect of moisture on masonry, design considerations, flashing materials, construction practices, and maintenance of flashing.
CAVITY WALLS
For cavity walls, as illustrated in Figure 1, the cavity typically ranges from a minimum of 2 in. to a maximum of 4 ½ in. (25 to 114 mm) wide, with a minimum of a 1 in. (25 mm) clear airspace if rigid insulation is placed in the cavity. Cavities wider than 4 ½ in. (114 mm) are permitted only if a detailed analysis is performed on the wall ties per the International Building Code and Building Code Requirements of Masonry Structures (refs. 2, 3) The 1 in. (25 mm) clear airspace works only if the mason takes precautions to insure that mortar will not bridge the airspace. Such precautions would include beveling the mortar bed away from the cavity or drawing a piece of wood up the cavity to collect mortar droppings. If precautions are not taken, it is suggested that a wider airspace be utilized, i.e. 1½ to 2 in (38 to 51 mm). Also when using glazed masonry veneer, a 2 in. (51 mm) minimum airspace is recommended with air vents provided at the top and bottom of the wall because of the impermeable nature of the unit. Proprietary insulated drainage boards or mats are available that provide an unobstructed drainage path that eliminate the need for a clear airspace (ref. 4).
As shown in Figure 1, the flashing in a cavity wall at the intersection of the foundation should be sealed to the exterior faceshell of the backup wythe, project downward to the foundation surface, outward to the exterior face of the wall, and terminate with a sloped drip. Weep holes or open head joints should be located a maximum of 32 in. (813 mm) apart. Flashing at lintels and sills (shown in Figures 2 and 3, respectively) is very similar. Although not shown, vents can be installed in the vertical head joints at the top of masonry walls to provide natural convective air flow within the cavity to facilitate drying. Prefabricated flashing boots available for both single and multiwythe walls are shown in Figure 7.
Figure 1—Flashing Cavity Walls at Foundations
Figure 2—Flashing Cavity Walls at Bond Beam Locations
Figure 3—Flashing Cavity Walls at Sills
SINGLE WYTHE WALLS
Flashings in single wythe walls, like cavity walls should be positioned to direct water to the exterior. This is normally accomplished using two narrower units to make up the thickness of the wall and placing flashing between them as shown in Figures 4 and 8. Care should be exercised to insure that surfaces supporting the flashing are flat or are sloping to the exterior. This can be accomplished by using solid units, lintel or closed bottom bond beam units turned upside down similar to Figure 3, or by filling cells of hollow units with mortar or grout.
Flashing of single wythe walls at lintels, foundations, and bond beams is accomplished in the same manner as shown in Figure 4 while sills are shown in Figure 6. Through-wall flashing is used in many areas of the country as shown in Figure 9. However, the bondbreaking effects of this type of detail need to be evaluated in regard to the structural performance of the wall. Additional information for flashing single-wythe walls, particularly architectural concrete masonry walls, and means for providing a higher level of structural continuity at flashings is contained in TEK 19-02B (ref. 5). Flashing single wythe walls at the ends of bar joists which utilize wall pockets for bearing is shown in Figures 8 and 8a.
Figure 4—Flashing Single Wythe Walls
Figure 5—Two-Piece Flashing Detail
Figure 6—Flashing Single Wythe Walls at Sills
Figure 7—Prefabricated Flashing Boots
FLASHINGS AT COPINGS AND CAPS
The type of flashing detail to use on low-sloped roofs will in part depend on the type of roofing membrane being used. As with any flashing detail, the materials used should result in a uniform and compatible design. For example, joining two materials with significantly different coefficients of thermal expansion (such as metal flashing and bitumen roofing membrane) can cause tearing and failure of the joint. Many roofing membranes also shrink as they age. As a result, roofing membranes extending over the top of a parapet may pull the parapet off the wall as the roofing membrane shrinks. Counter flashing provides a solution to these problems as shown in Figure 8. Counter flashing also facilitates the reroofing process by allowing easy removal and access to the flashing membrane fasteners.
During placement of the final courses of masonry in parapets, and commencing with the second course below the coping/cap location, a grout stop should be placed over cores so that grout can be placed for the positioning of anchor bolts (Figure 8).
In coping installations it is imperative that penetrations of through-wall flashing be tightly sealed to prevent water infiltration. A full mortar bed is required to be placed on the through-wall flashing to allow proper positioning of coping units. Full head joints are placed between the coping units as well as properly spaced control joints. The joints between the coping units should then be raked and a joint sealant applied.
Coping units should be sized such that overhangs and a drip reveal are provided on both sides of the wall. Metal caps require wood plates for anchorage, which in turn are usually attached to the wall with anchor bolts. The cap should be sloped to prevent water from draining onto the exposed surface of the masonry and should extend at least 4 in. (102 mm) over the face of the masonry and sealed on both sides. Smooth face or uniform split face CMU should be considered for use under the cap to ensure a relatively tight fit between the masonry and cap that might be hindered by uneven concrete masonry units such as split-face or fluted units.
Figure 8a—Isometric of Flashing Around End of Joist (ref. 6)
Figure 8—Flashing Single Wythe Walls at Roof/Parapet Intersection (ref. 6)
INTERIOR WALL TREATMENTS
Concrete masonry walls with an interior treatment may also utilize a through-wall flashing installation of flashings as shown in Figure 9. However, as noted in the figure, through-wall flashings generally create a bond-breaker, which reduces the structural capacity of a masonry wall. This effect should be carefully evaluated before implementing this type of detail particularly in high-wind and seismic areas.
As shown in Figure 9, the flashing should project through the wall and be carried up on the interior concrete masonry surface. Furring strips installed to receive the plastic vapor retarder and the interior gypsum board will hold the flashing in position. This procedure permits any water that may penetrate to the interior surface of the concrete masonry wall to drain out at the base of the wall. Weep holes should project completely through the wall thickness. Vents, if used, should project into the core areas only.
Figure 9—Through-Wall Flashing
SPLICING FLASHING
When it is necessary to splice the flashing, extra precautions are required to ensure that these discreet locations do not become sources of water penetration. Flashing should be longitudinally continuous or terminated with an end dam as shown in Figure 7. The splicing of flashing materials consisting of plastic and rubber compounds is acheived by overlapping the joint a minimum distance of 4 in. (102 mm). The lapped area is then bonded together with adhesive if the flashing material is not self-adhering.
Lap splicing of metal flashing is not recommended as it has a different coefficient of thermal expansion than that of concrete masonry. As the temperature fluctuates, the flashing material will expand and contract differently than the masonry material, which can result in sealant failure and a potential point of entry for moisture. A typical flashing splice is detailed in Figure 10. Here, two sections of sheet metal type flashing that are to be spliced are first installed with a ¼-in. (6.4 mm) gap between them to allow for expansion of the flashing. Next, a section of pliable self-adhering membrane (such as rubberized-asphalt) or other pliable membrane set in mastic is fully bonded to the flashing at the location of the gap.
Figure 10—Splicing Metal Flashing
REFERENCES
Flashing Strategies for Concrete Masonry Walls, TEK 1904A, Concrete Masonry & Hardscapes Association, 2008.
International Building Code. International Code Council, 2003 and 2006.
Building Code Requirements for Masonry Structures, ACI 530/ASCE 5/TMS 402, reported by the Masonry Standards Joint Committee, 2002 and 2005.
Flashing…Tying the Loose Ends, Masonry Advisory Council, Chicago, IL, 1998.
Design for Dry Single-Wythe Concrete Masonry Walls, TEK 19-02B, Concrete Masonry & Hardscapes Association, 2012.
Generic Wall Design, Masonry Institute of Michigan, 1998.
Masonry connectors can be classified as wall ties, anchors or fasteners. Wall ties connect one masonry wythe to an adjacent wythe. Anchors connect masonry to a structural support or frame. Fasteners connect an appliance to masonry. This TEK covers metal wall ties and anchors. Fasteners are discussed in TEK 12-05 (ref. 1).
The design of anchors and ties is covered by the International Building Code and Building Code Requirements for Masonry Structures (refs. 2, 3).These provisions require that connectors be designed to resist applied loads and that the type, size and location of connectors be shown or indicated on project drawings. This TEK provides a guide to assist the designer in determining anchor and tie capacity in accordance with the applicable standards and building code requirements.
DESIGN CRITERIA
Connectors play a very important role in providing structural integrity and good serviceability. As a result, when selecting connectors for a project, designers should consider a number of design criteria. Connectors should:
Transmit out-of-plane loads from one wythe of masonry to another or from masonry to its lateral support with a minimum amount of deformation. It is important to reduce the potential for cracking in masonry due to deflection. There is no specific criteria on connector stiffness, but some authorities suggest that a stiffness of 2,000 lb/in. (350 kN/m) is a reasonable target.
Allow differential in-plane movement between two masonry wythes connected with ties. This is especially significant as more insulation is used between the outer and inner wythes of cavity walls and where wythes of dissimilar materials are anchored together. On the surface, it may appear that this criterion is in conflict with Item 1, but it simply means that connectors must be stiff in one direction (out-of-plane) and flexible in the other (in plane). Note that some connectors allow much more movement than unreinforced masonry can tolerate (see ref. 27 for a discussion of potential masonry wall movements). In order to preserve the in-plane and out-of-plane wall tie stiffness, current codes (refs. 2, 3) allow cavity widths up to 4 1/2 in. (114 mm) without performing wall tie analysis. With an engineered analysis of the wall ties, cavity widths may be significantly increased to accommodate thicker insulation.
Meet applicable material requirements:
plate and bent-bar anchors—ASTM A36 (ref. 4)
sheet-metal anchors and ties—ASTM A1008 (ref. 5)
wire anchors and ties—ASTM A82 (ref. 6), and adjustable wire ties must also meet the requirements illustrated in Figure 1
wire mesh ties – ASTM A185 (ref. 7)
Provide adequate corrosion protection. Where carbon steel ties and anchors are specified, corrosion protection must be provided by either galvanizing or epoxy coating in conformance with the following (ref. 8):
A. Galvanized coatings:
Joint reinforcement in interior walls exposed to a mean relative humidity of 75% or less—ASTM A641 (ref. 13), 0.1 oz zinc/ft2 (0.031 kg zinc/m2)
Joint reinforcement, wire ties and wire anchors, exterior walls or interior walls exposed to a mean relative humidity greater than 75%—ASTM A153 (ref. 14), 1.5 oz zinc/ft2 (458 g/m2)
Sheet metal ties or anchors, interior walls exposed to a mean relative humidity of 75% or less—ASTM A653 (ref. 15) Coating Designation G60
Sheet metal ties or anchors, exterior walls or interior walls exposed to a mean relative humidity greater than 75%—ASTM A153 Class B
Steel plates and bars, exterior walls or interior walls exposed to a mean relative humidity greater than 75%—ASTM A123 (ref. 16) or ASTM A153 Class B
Plate and bent-bar anchors—ASTM A480 and ASTM A666 (refs. 10, 11)
Sheet metal anchors and ties—ASTM A480 and ASTM A240 (refs. 10, 12)
Wire ties and anchors—ASTM A580
B. Epoxy coatings:
Joint reinforcement—ASTM A884 (ref. 17) Class A Type 1 > 7 mils (175 µm)
Wire ties and anchors—ASTM A899 (ref. 18) Class C 20 mils (508 µm)
Sheet metal ties and anchors—20 mils (508 µm) per surface or per manufacturer’s specification
Where stainless steel anchors and ties are specified, Specification for Masonry Structures (ref. 8) requires that AISI Type 304 or 316 stainless steel be provided that complies with:
Joint reinforcement—ASTM A580 (ref. 9)
Accommodate construction by being simple in design and easy to install. Connectors should not be so large and cumbersome as to leave insufficient room for mortar in the joints, which can result in a greater tendency to allow water migration into the wall. In the same way, connectors should readily accommodate insulation in wall cavities.
WALL TIE AND ANCHOR REQUIREMENTS
Multiwythe Masonry Wall Types
Wall ties are used in all three types of multiwythe walls (composite, noncomposite and veneer), although some requirements vary slightly depending on the application. The primary differences between these wall systems are in construction details and how the applied loads are assumed to be distributed.
Composite walls are designed so that the masonry wythes act together as a single structural member. This requires the masonry wythes to be connected by masonry headers or by a mortar- or grout filled collar joint and wall ties to help ensure adequate load transfer. TEKs 16-01A and 16-02B (refs. 19, 20) more fully describe composite walls.
In noncomposite masonry (also referred to as a cavity wall), wythes are connected with metal wall ties, but they are designed such that each wythe individually resists the loads imposed on it. Noncomposite walls are discussed in TEKs 16-01A and 16-04A (refs. 19, 21).
In a veneer wall, the backup wythe is designed as the load-resisting system, with the veneer providing the architectural wall finish. Information on veneer walls can be found in TEKs 05-01B and 03 06C (refs. 22, 23). Note that although a cavity wall is defined as a noncomposite masonry wall (ref. 3), the term cavity wall is also commonly used to describe a veneer wall with masonry backup.
Building Code Requirements for Masonry Structures also includes empirical requirements for wire wall ties and strap-type ties used to connect intersecting walls. These requirements are covered in TEK 14-08B (ref. 24).
Wall Ties
Wire wall ties can be either one piece unit ties, adjustable two piece ties, joint reinforcement or prefabricated assemblies made up of joint reinforcement and adjustable ties (see Figure 2). Note that the 2011 edition of Specification for Masonry Structures allows adjustable pintle ties to have only one leg (previously, two legs were required for this type of wall tie).
Wall ties do not have to be engineered unless the nominal width of the wall cavity is greater than 4 1/2 in. (114 mm). These wall tie analyses are becoming more common as a means to accommodate more thermal insulation in the wall cavity. Masonry cavities up to 14 in. (356 mm) have been engineered. Of note for these analyses is that the span of wire is a more critical factor than cavity width, i.e. the span length of the pintel component typically controls the mode of failure.
The prescribed size and spacing is presumed to provide connections that will be adequate for the loading conditions covered by the code. These wall tie spacing requirements can be found in TEK 03-06C (for veneers) and TEK 16-01A (for composite and noncomposite walls). Note that truss-type joint reinforcement is stiffer in the plane of a wall compared to ladder-type, so it is more restrictive of differential movement. For this reason, laddertype joint reinforcement is recommended when significant differential movement is expected between the two wythes or when vertical reinforcement is used. See TEK 12-02B (ref. 25) for more information.
Additional tests are needed for adjustable anchors of different configurations and for one piece anchors. Proprietary anchors are also available. Manufacturers of proprietary anchors should furnish test data to document comparability with industry-tested anchors.
Anchors are usually designed based on their contributory area. This is the traditional approach, but some computer models suggest that this approach does not always reflect the actual behavior of the anchorage system. However, there is currently no accepted computer program to address this point, so most designers still use the contributory area approach with a factor of safety of three. The use of additional anchors near the edges of wall panels is also recommended and required around large openings and within 12 in. (305 mm) of unsupported edges.
CONSTRUCTION
When typical ties and anchors are properly embedded in mortar or grout, mortar pullout or pushout will not usually be the controlling mode of failure. Specification for Masonry Structures requires that connectors be embedded at least 1 1/2 in. (38 mm) into a mortar bed of solid units. The required embedment of unit ties in hollow masonry is such that the tie must extend completely across the hollow units. Proper embedment can be easily attained with the use of prefabricated assemblies of joint reinforcement and unit ties. Because of the magnitude of loads on anchors, it is recommended that they be embedded in filled cores of hollow units. See TEK 03-06C for more detailed information.
REFERENCES
Fasteners for Concrete Masonry, TEK 12-05. Concrete Masonry & Hardscapes Association, 2005.
International Building Code. International Code Council, 2012.
Building Code Requirements for Masonry Structures, TMS 402-11/ACI 530-11/ASCE 5-11. Reported by the Masonry Standards Joint Committee, 2011.
Standard Specification for Carbon Structural Steel, A36-ASTM International, 2008.
Standard Specification for Steel, Sheet, Cold-Rolled, Carbon, Structural, High-Strength Low-Alloy with Improved Formability, A1008-11. ASTM International, 2011.
Standard Specification for Steel Wire, Plain for Concrete Reinforcement, A82-07. ASTM International, 2007.
Standard Specification for Steel Welded Wire Reinforcement, Plain, for Concrete, A185-07. ASTM International, 2007.
Specification for Masonry Structures, TMS 602 -11/ACI 530.1-11/ASCE 6-11. Reported by the Masonry Standards Joint Committee, 2011.
Standard Specification for Stainless Steel Wire, ASTM A580-08. ASTM International, 2008.
Standard Specification for General Requirements for Flat Rolled Stainless and Heat-Resisting Steel Plate, Sheet, and Strip, ASTM A480-11a. ASTM International, 2011.
Standard Specification for Annealed or Cold-Worked Austenitic Stainless Steel, Sheet, Strip, Plate and Flat Bar, ASTM A666-10. ASTM International, 2010.
Standard Specification for Chromium and Chromium Nickel Stainless Steel Plate, Sheet and Strip for Pressure Vessels and for General Applications, ASTM A240-11a. ASTM International, 2011.
Standard Specification for Zinc-Coated (Galvanized) Carbon Steel Wire, ASTM A641-09a. ASTM International, 2009.
Standard Specification for Zinc Coating (Hot-Dip) on Iron and Steel Hardware, ASTM A153-09. ASTM International, 2009.
Standard Specification for Steel Sheet, Zinc-Coated Galvanized or Zinc-Iron Alloy-Coated Galvannealed by the Hot-Dip Process, ASTM A653-10. ASTM International, 2010.
Standard Specification for Zinc (Hot-Dip Galvanized) Coating on Iron and Steel Products, ASTM A123-09. ASTM International, 2009.
Standard Specification for Epoxy-Coated Steel Wire and Welded Wire Fabric for Reinforcement, ASTM A884-06. ASTM International, 2006.
Standard Specification for Steel Wire Epoxy Coated, ASTM A899-91(2007). ASTM International, 2007.
Empirical Design of Concrete Masonry Walls, TEK 14-08B, Concrete Masonry & Hardscapes Association, 2008.
Joint Reinforcement for Concrete Masonry, TEK 12-02B, Concrete Masonry & Hardscapes Association, 2005.
Porter, Max L., Lehr, Bradley R., Barnes, Bruce A., Attachments for Masonry Structures, Engineering Research Institute, Iowa State University, February 1992.
Crack Control Strategies for Concrete Masonry Construction, CMU-TEC-009-23, Concrete Masonry & Hardscapes Association, 2023.
In addition to its structural use or as the exterior wythe of composite and noncomposite walls, concrete brick and architectural facing units are also used as veneer over various backing surfaces. The variety of surface textures, colors, and patterns available makes concrete masonry a versatile and popular exterior facing material. Architectural units such as split-face, scored, fluted, ground face, and slump are available in a variety of colors and sizes to complement virtually any architectural style.
VENEER—DESIGN CONSIDERATIONS
Veneer is a nonstructural facing of brick, stone, concrete masonry or other masonry material securely attached to a wall or backing. Veneers provide the exterior wall finish and transfer out-of-plane loads directly to the backing, but they are not considered to add to the load-resisting capacity of the wall system. Backing material may be masonry, concrete, wood studs or steel studs.
There are basically two types of veneer—anchored veneer and adhered veneer. They differ by the method used to attach the veneer to the backing, as illustrated in Figure 1. Unless otherwise noted, veneer requirements are those contained in the International Building Code (IBC) and Building Code Requirements for Masonry Structures (refs. 2, 3).
For the purposes of design, veneer is assumed to support no load other than its own weight. The backing must be designed to support the lateral and in some instances the vertical loads imposed by the veneer in addition to the design loads on the wall, since it is assumed the veneer does not add to the strength of the wall.
Masonry veneers are typically designed using prescriptive code requirements that have been developed based on judgement and successful performance. The prescriptive requirements relate to size and spacing of anchors and methods of attachment, and are described in the following sections. The assembly can be designed as a noncomposite cavity wall where the out-of-plane loads are distributed to the two wythes in proportion to their relative stiffness. Design criteria are provided in IBC Chapter 16 as well as in TEK 16-04A, Design of Concrete Masonry Noncomposite (Cavity) Walls, (ref. 4).
In addition to structural requirements, differential movement between the veneer and its supports must be accommodated. Movement may be caused by temperature changes, moisture-volume changes, or deflection. In concrete masonry, control joints and horizontal joint reinforcement effectively relieve stresses and accommodate small movements. For veneer, control joints should generally be placed in the veneer at the same locations as those in the backing, although recommended control joint spacing can be adjusted up or down based on local experience, the aesthetic requirements of the project, or as required to prevent excessive cracking. See CMU-TEC 009-23, Crack Control for Concrete Brick and Other Concrete Masonry Veneers (ref. 5), for further information.
For exterior veneer, water penetration into the cavity is anticipated. Therefore, the backing system must be designed and detailed to resist water penetration and prevent water from entering the building. Flashing and weeps in the veneer collect any water that penetrates the veneer and redirects it to the exterior. Partially open head joints are one preferred type of weep. They should be at least 1 in. (25 mm) high and spaced not more than 32 in. (813 mm) on center. If necessary, insects can be thwarted by inserting stainless steel wool into the opening or by using proprietary screens. For anchored veneer, open weeps can also serve as vents, allowing air circulation in the cavity to speed the rate of drying. Additional vents may be installed at the tops of walls to further increase air circulation. More detailed information is contained in TEK 05-01B, Concrete Masonry Veneer Details, TEK 19-04A, Flashing Strategies for Concrete Masonry Walls, and TEK 19-05A, Flashing Details for Concrete Masonry Walls (refs. 1, 6, 7).
ANCHORED VENEER
Anchored veneer is veneer which is supported laterally by the backing and supported vertically by the foundation or other structural elements. Anchors are used to secure the veneer and to transfer loads to the backing. Anchors and supports must be noncombustible and corrosion-resistant.
The following prescriptive criteria apply to anchored veneer in areas with velocity pressures, qz, up to 40 psf (1.92 kPa). Modified prescriptive criteria is available for areas with qz greater than 40 psf (1.92 kPa) but not exceeding 55 psf (2.63 kPa) with a building mean roof height up to 60 ft (18.3 m). These modified provisions are presented in the section High Wind Areas. In areas where qz exceeds 55 psf (2.63 kPa), the veneer must be designed using engineering philosophies, and the following prescriptive requirements may not be used.
In areas where seismic activity is a factor, anchored veneer and its attachments must meet additional requirements to assure adequate performance in the event of an earthquake. See the section Seismic Design Categories C and Higher for details.
Masonry units used for anchored veneer must be at least 2 ⅝ in. (67 mm) thick.
A 1 in. (25 mm) minimum air space must be maintained between the anchored veneer and backing to facilitate drainage. A 1 in. (25 mm) air space is considered appropriate if special precautions are taken to keep the air space clean (such as beveling the mortar bed away from the cavity). Otherwise, a 2 in. (51 mm) air space is preferred. As an alternative, proprietary insulating drainage products can be used.
The maximum distance between the inside face of the veneer and the outside face of the backing is limited to 4 ½ in. (114 mm), except for corrugated anchors used with wood backing, where the maximum distance is 1 in. (25 mm).
When anchored veneer is used as an interior finish supported on wood framing, the veneer weight is limited to 40 lb/ft2 (195 kg/m2).
Deflection Criteria
Deflection of the backing should be considered when using masonry veneer, in order to control crack width in the veneer and provide veneer stability. This is primarily a concern when masonry veneer is used over a wood or steel stud backing. Building Code Requirements for Masonry Structures, however, does not prescribe a deflection limit for the backing. Rather, the commentary presents various recommendations for deflection limits.
For anchored veneer, Chapter 16 of the International Building Code requires a deflection limit of l/240 for exterior walls and interior partitions with masonry veneer.
Support of Anchored Veneer
The height and length of the veneered area is typically not limited by building code requirements. The exception is when anchored veneer is applied over frame construction. For wood stud backup, veneer height is limited to 30 ft (9.14 m) (height at plate) or 38 ft (11.58 m) (height at gable). Similarly, masonry veneer over steel stud backing must be supported by steel shelf angles or other noncombustible construction for each story above the first 30 ft (9.14 m) (height at plate) or 38 ft (11.58 m) (height at gable). This support does not necessarily have to occur at the floor height, for example it can be provided at a window head or other convenient location.
Exterior anchored veneer is permitted to be supported on wood construction under the following conditions:
the veneer has an installed weight of 40 psf (195 kg/m2) or less,
the veneer has a maximum height of 12 ft (3.7 m),
a vertical movement joint in the veneer is used to isolate the veneer supported on wood construction from that supported by the foundation,
masonry is designed and constructed so that the masonry is not in direct contact with the wood, and
the horizontally spanning member supporting the masonry veneer is designed to limit deflection due to unfactored dead plus live loads to l/600 or 0.3 in. (7.5 mm).
Over openings, the veneer must be supported by non- combustible lintels or supports attached to noncombustible framing, as shown in Figure 2.
The following requirements assume that the veneer is laid in running bond. When other bond patterns are used, the veneer is required to have joint reinforcement spaced no more than 18 in. (457 mm) on center vertically. The joint reinforcement need only be one wire, with a minimum size of W1.7 (MW11).
Figure 2—Steel Lintel Flashing Detail (ref. 8)
(backing not shown for clarity)
Anchors
Veneers may generally be anchored to the backing using sheet metal anchors, wire anchors, joint reinforcement or adjustable anchors, although building codes may restrict the use of some anchors. Corrugated sheet metal anchors are permitted with masonry veneer attached to wood backing only. Requirements for the most common anchor types are summarized in Figures 3 through 5 and Table 1. As an alternative, adjustable anchors of equivalent strength and stiffness may be used. Cavity drips are not permitted. See TEK 12-01B, Anchors and Ties for Masonry, (ref. 9) for detailed information on anchor materials and requirements.
Attachment to Backing
When masonry veneer is anchored to wood backing, each anchor is attached to the backing with a corrosion- resistant 8d common nail, or a fastener with equivalent or greater pullout strength. For proper fastening of corrugated sheet metal anchors, the nail or fastener must be located within ½ in. (13 mm) of the 90° bend in the anchor. The exterior sheathing must be either water resistant with taped joints or be protected with a water- resistant membrane, such as building paper ship-lapped a minimum of 6 in. (152 mm) at seams, to protect the backing from any water which may penetrate the veneer.
When masonry veneer is anchored to steel backing, adjustable anchors must be used to attach the veneer. Each anchor is attached with corrosion-resistant screws that have a minimum nominal shank diameter of 0.19 in. (4.8 mm), or an anchor with equivalent pullout strength. Cold-formed steel framing must be corrosion resistant and should have a minimum base metal thickness of 0.043 in. (1.1 mm). Sheathing requirements are the same as those for wood stud backing.
Masonry veneer anchored to masonry backing may be attached using wire anchors, adjustable anchors or joint reinforcement. Veneer anchored to a concrete backing must be attached with adjustable anchors.
Figure 3—Adjustable Anchors
Figure 4—Corrugated Sheet Metal Anchor Requirements
Anchor Placement
When typical ties and anchors are properly embedded in mortar or grout, mortar pullout or pushout will not usually be the controlling mode of failure. For this reason, connectors must be embedded at least 1 ½ in. (38 mm) into a mortar bed of solid units, and the mortar bed joint must be at least twice the thickness of the embedded anchor. The required embedment of unit ties in hollow masonry is such that the tie must extend completely across the hollow units (Figure 6). Proper embedment can be easily attained with the use of prefabricated assemblies of joint reinforcement and unit ties. Because of the magnitude of loads on anchors, it is recommended that they be embedded in filled cores of hollow units. To save mortar, screens can be placed under the anchor and 1 to 2 in. (25 to 51 mm) of mortar can be built up into the core of the block above the anchor (Figure 7).
Figure 5—Requirements for Joint Reinforcement Used to Anchor Veneer
Figure 6—Minimum Embedment of Joint Reinforcement and Wire Ties
Figure 7—Use of Mesh to Facilitate Embedment of Anchor in Mortar
High Wind Areas
In areas with qz greater than 40 psf (1.92 kPa) but not exceeding 55 psf (2.63 kPa) with a building mean roof height up to 60 ft (18.3 m), the following modified prescriptive provisions may be used.
The modified prescriptive provisions are:
the maximum wall area supported by each anchor must be reduced to 70% of the value listed in Table 1,
anchor spacing is reduced to a maximum of 18 in. (457 mm), both vertically and horizontally, and
around openings larger than 16 in. (406 mm) in either direction, anchors must be placed within 12 in. (305 mm) of the opening and spaced at 24 in. (610 mm) on center or less.
In areas where qz exceeds 55 psf (2.63 kPa), the veneer must be designed using engineering philosophies.
Seismic Design Categories C and Higher
To improve veneer performance under seismic loading in Seismic Design Category (SDC) C, the sides and top of the veneer must be isolated from the structure, so that vertical and lateral seismic forces are not transferred to the veneer. This reduces accidental loading and allows more building deflection without causing damage to the veneer.
In SDC D, in addition to this isolation, the maximum wall area supported by each anchor must be reduced to 75% of the value listed in Table 1, although the maximum spacings are unchanged. In addition, when the veneer is anchored to wood backing, the veneer anchor must be attached to the wood using a corrosion-resistant 8d ring-shank nail, a No. 10 corrosion- resistant screw with a minimum nominal shank diameter of 0.190 in. (4.8 mm), or with a fastener having equivalent or greater pullout strength.
In SDC E and F, the requirements listed above for SDC C and D must be met, as well as the additional requirements listed here. The weight of each story of anchored veneer must be supported independently of other stories to help limit the size of potentially damaged areas. In addition, to improve veneer ductility the veneer must have continuous W1.7 (MW11) single wire joint reinforcement at 18 in. (457 mm) o.c. or less vertically, with a mechanical attachment to the anchors, such as clips or hooks.
ADHERED VENEER
Conventional adhered veneer is veneer secured and supported through adhesion with a bonding material applied over a backing that both meets required deflection limits and provides for necessary adhesion. When applied to a masonry or concrete backing, the veneer may be applied directly to the backing substrate using layers of neat cement paste and Type S mortar, as illustrated in Figure 1. When applied over steel or wood framing, the adhered masonry veneer is applied to a metal lath and portland cement plaster backing placed against the sheathing element and attached to the stud framing members.
Alternative design of adhered veneer is permitted under the International Building Code when in compliance with Building Code Requirements for Masonry Structures (MSJC), where the requirements of unit adhesion (shear stress > 50 psi, 345 kPa) are met, out-of-plane curvature of the backing is limited to prevent the veneer from separating from the backing, and freeze thaw cycling, water penetration, and air and water vapor transmission are considered. Although the MSJC does not stipulate a deflection limit to control out-of-plane curvature, the Tile Council of America limits the deflection of backing supporting ceramic tiles to l/360 (ref. 11). Similarly, IBC Chapter 16 (for engineered design) requires a deflection limit of l/360 for exterior walls and interior partitions with plaster or stucco, which would be similar to an adhered veneer application.
Proprietary polymer-fortified adhesive mortars exist that meet the adhesion requirements and are used as a mortar setting bed to adhere the masonry veneers directly to a masonry or concrete backing, or to a lath and plaster backing system over wood or steel studs.
In addition, several proprietary systems are available to aid in placement of adhered masonry veneer on suitable exterior or interior substrates. These typically take the form of galvanized steel support panels that are mechanically anchored to a masonry or concrete backing, or placed against the sheathing element and attached to stud framing members. These products essentially take the place of the metal lath in the adhered veneer application. The metal panels contain support tabs and other features to facilitate the veneer application, carry the dead load of the veneer, and improve bonding of the veneer to the panel. In some cases, metal panel systems provide drainage or air flow channels as well. In lieu of mortar, construction adhesives having a shear bond strength greater than 50 psi (345 kPa) are used to bond the masonry veneer to the panel and masonry pointing mortar is used to fill the joint space between the masonry units. Installation using these products should follow manufacturer’s instructions.
Masonry units used in this application are limited to 2 ⅝ in. (67 mm) thickness, 36 in. (914 mm) in any face dimension, 5 ft2 (0.46 m2) in total face area and 15 lb/ft2 (73 kg/m2 ) weight. In addition, the International Building Code (ref. 4) stipulates: a minimum thickness of 0.25 in. (6.3 mm) for weather-exposed adhered masonry veneer; and, for adhered masonry veneers 2 used on interior walls, a maximum weight of 20 lb/ft2 (97 kg/ m2).
When an interior adhered veneer is supported by wood construction, the wood supporting member must be designed for a maximum deflection of 1/600 of its span.
Adhered veneer and its backing must also be designed to either:
have sufficient bond to withstand a shearing stress of 50 psi (345 kPa) based on the gross unit surface area when tested in accordance with ASTM C482, Standard Test Method for Bond Strength of Ceramic Tile to Portland Cement Paste (ref. 10), or
be installed according to the following:
A paste of neat portland cement is brushed on the backing and on the back of the veneer unit immediately prior to applying the mortar coat. This neat cement coating provides a good bonding surface for the mortar.
Type S mortar is then applied to the backing and to each veneer unit in a layer slightly thicker than ⅜ in. (9.5 mm). Sufficient mortar should be used so that a slight excess is forced out the edges of the units.
The units are then tapped into place to eliminate voids between the units and the backing which could reduce bond. The resulting thickness of mortar between the backing and veneer must be between ⅜ and ¼ in. (9.5 and 32 mm).
Mortar joints are tooled with a round jointer when the mortar is thumbprint hard.
When applied to exterior stud walls, the IBC requires adhered masonry veneer to include a screed or flashing at the foundation. In addition, minimum clearances must be maintained between the bottom of the adhered veneer and paved areas, adjacent walking surfaces and the earth.
Backing materials for adhered veneer must be continuous and moisture-resistant (wood or steel frame backing with adhered veneer must be backed with a solid water repellent sheathing). Backing may be masonry, concrete, metal lath and portland cement plaster applied to masonry, concrete, steel framing or wood framing. Note that care must be taken to limit deflection of the backing, which can cause veneer cracking or loss of adhesion, when adhered masonry veneer is used on steel frame or wood frame backing. The surface of the backing material must be capable of securing and supporting the imposed loads of the veneer. Materials that affect bond, such as dirt, grease, oil, or paint (except portland cement paint) need to be cleaned off the backing surface prior to adhering the veneer.
NOTATIONS:
l = clear span between supports, in. (mm)
qz = velocity pressure evaluated at height z above ground, in.-lb/ft2 (kPa)
