By Robert M. Chamra, PE This paper was presented at the 2025 IIBEC International Convention and Trade Show.
MASONRY VENEER IS a well-known and commonly used cladding system found in the built environment due to its aesthetic possibilities and durability. Historically, this “nonstructural” element has fallen under the architect’s purview in the design process, but with increasing complexity in building performance and geometry, building enclosure consultants are frequently joining the design team for, or providing third-party design review of, masonry veneer construction. When project demands require masonry to exceed the prescriptive design limitations, engineered design of masonry veneer is required. The 2022 edition of The Masonry Society’s TMS 402/6021 includes engineered design methods, which allow for new design and construction possibilities for masonry veneer beyond prescriptive limitations. A BRIEF USE AND CODE HISTORY OF MASONRY VENEER ASTM International defines masonry as “the type of construction made of manufactured masonry units laid with mortar, grout, or other methods of joining,”2 although colloquially, natural stone or “dimension stone” unit assemblies are regularly referred to as masonry veneer as well. Natural stone masonry structures, such as ancient Egyptian pyramids, have existed for millennia, so users of masonry as a building material have expectations that it will be durable. Subsequently, mass masonry structures used multiple layers, or wythes, of smaller masonry units to maintain the durability and aesthetics of the ancient structures with improved constructability. Nonetheless, mass masonry walls remained a labor-intensive construction method. In modern construction, masonry veneer was the next evolution to decrease installation costs. The Masonry Society (TMS) defines masonry veneer as “a masonry wythe that provides the exterior finish of a wall system and transfers out-of-plane load directly to a backing but is not
considered to add strength or stiffness to the wall system.”1 Masonry veneer can be broken into two attachment categories: anchored veneer and adhered veneer. An anchored veneer assembly transfers out-of-plane load to the backing predominantly through veneer ties (Item 32 in Fig. 1).3 An adhered masonry veneer assembly transfers out-of-plane load to the backing through either direct bond or mechanical fasteners and lath into the backing (Item 40 in Fig. 2).4 Unlike mass masonry walls, masonry veneer typically contains a drainage cavity and associated accessory products to expel incidental water that penetrates the porous masonry units and mortar. The detailing to prevent bulk water infiltration and provide lateral attachment of the masonry veneer is critical to maintain the durability and safety of masonry cladding. The code history for masonry veneer is relatively short, as summarized in Table 1. The masonry veneer standard referenced in the 2024 International Building Code5 is TMS 402/602-22.1 As the numbering suggests, the document is split into two sections: the design code (TMS 402) and the construction specification (TMS 602). TMS 602 includes the minimum construction requirements that can be incorporated into design specifications and drawing notes by reference. TMS 402 includes the remaining design requirements that must be defined in either the design specifications or drawings to convey the intended masonry veneer design for a given project. To avoid misinterpretation of the design intent, TMS 402 cannot be incorporated into design documents by reference.
PRESCRIPTIVE DESIGN OF MASONRY VENEER Before diving into engineered design, it is important to note that prescriptively designed masonry veneer is allowed and used in many situations. This overview of the prescriptive design requirements is intended to differentiate the circumstances where each design method is appropriate. A good starting point for the discussion is the masonry unit materials used within the veneer. Figure 3 can be found in the commentary to TMS 402/602-22.1 While compliance with code commentary is not required for design or construction, this particular table summarizes the specific unit requirements in the subsequent prescriptive and engineered veneer sections. Dimension stone is defined as “natural stone that has been selected and fabricated to specific sizes and shapes.”1 The properties of natural stone inherently vary depending on the type of material and location of the quarry. Because naturally occurring materials cannot be standardized like manufactured masonry units, anchored dimension stone veneer design requires material testing to determine the compressive strength, durability, and mortar bond strength. The results of the testing determine whether the design assumptions were correct, or revisions are needed to meet the design intent. Therefore, the design of all anchored dimension stone masonry veneer must be engineered. Seismic design category and wind pressure control the permitted design method (Fig. 4). Strength-level design wind pressures for masonry veneer (pveneer) are determined using the ASCE/SEI 7 Chapter 30 components and cladding provisions, including, but not limited to, surrounding topographical conditions, required design wind speeds, and total height.6 Sites located at the top of a hill or in a dense, urban area will naturally experience higher wind pressures. Proximity to coasts or mountains will increase the required wind speeds and the correlating wind pressures. Wind pressures also increase with height above grade, so midrise and high-rise buildings may require an adjustment of the masonry veneer design along the height or near building corners. Seismic activity provides another source of lateral loading on masonry veneer. Due to the mass of the anchored masonry veneer, high-seismic areas (Seismic Design Category D and higher) require more restrictive design provisions regardless of wind pressures. As a result, the anchored veneer prescriptive design method in TMS 402 was split into basic and enhanced provisions for veneer tie spacing (Table 2). Simply stated, as lateral loads from
wind or seismic increase, the maximum veneer tie spacing decreases to maintain the same assumed load per veneer tie. Correspondingly, prescriptive adhered masonry veneer provisions are limited to a maximum wind pressure pveneer of 60 lb/ft² (2.87 kPa). For Seismic Design Category D and higher, the required mechanical fastener spacings for securing lath over wood and coldformed metal framing are reduced to 80% for adhered masonry
veneer.1 Lastly, the maximum height allowed for prescriptively designed adhered masonry veneer is limited to 60 ft (18.3 m) above grade. The prescriptive design method is based upon the masonry unit limitations shown in Table 3. Any masonry units not meeting the criteria in Table 3 must use the engineered design method. For anchored masonry veneer, the mortar joint width is also required to be at least twice the thickness of embedded tie materials. For example, a mortar joint containing a 3/16 in. (4.76 mm) diameter wire tie must be at least 3/8 in. (9.53 mm) wide. Anchored veneer mortar type must also be specified; Type N is commonly used in anchored veneer for balance in strength and stiffness. TMS 402/602-22 prescriptively requires the setting bed mortar for adhered veneer units to be a polymer-modified mortar for superior bond.1 Mortar materials greatly impact the overall performance of the masonry veneer, so it is critical that the design intent is conveyed within the design documents. Figure 5 illustrates the different veneer tie types referenced in TMS 402/602. The 2022 edition reorganized the previous prescriptive anchored veneer requirements into tables limited to the type of backing (Fig. 6) and the selected veneer tie type (Fig. 7). While it is not the intent of this paper to review each of the prescriptive design requirements for anchored veneer, Fig. 6 and 7 are included because they are referred to within the engineered design requirements of anchored masonry veneer that are discussed later. Dependent upon the backing type, different veneer tie types are allowed in the prescriptive design requirements. For each veneer tie type, the prescriptive design requirements include but are not limited to the following: • Maximum specified cavity width • Fastener type
• Fastener diameter • Fastener length • Veneer tie dimensions TMS 402/602-22 includes general requirements for both anchored and adhered veneer regarding water-penetration resistance and accommodation for differential movement. Due to an ever-changing array of building enclosure materials, specific flashing and drainage components are not explicitly mentioned by TMS 402/602-22. Differential movement encompasses thermal, moisture, and structural movements, which must be accommodated to avoid the masonry veneer providing unintended restraint, and associated potential future distress conditions, of the completed building system. ENGINEERED DESIGN OF MASONRY VENEER The following conditions, though not intended to be exhaustive of all design scenarios, exceed the prescriptive design methods discussed previously and must be engineered: • Anchored dimension stone veneer (Fig. 3) • Anchored veneer with components and cladding wind pressures exceeding 75 lb/ft2 (366 kg/m2) (Fig. 4) • Anchored veneer with veneer tie spacing tributary area or spacing exceeding the basic prescriptive and enhanced prescriptive maximum requirements (Table 2) • Anchored veneer masonry units less than 2.625 in. (66.7 mm) or greater than 5 in. (127 mm) in depth, or greater than 16 in. (406 mm) in height (Table 3) • Anchored veneer masonry units with weights exceeding 50 lb/ft2 (244 kg/m2) (Table 3) • Anchored veneer or veneer ties not compliant with prescriptive limitations (Fig. 6 and 7) • Adhered veneer with components and cladding wind pressures exceeding 60 lb/ft2 (2.87 kPa) • Adhered veneer exceeding a height of 60 ft (18.3 m) above grade • Adhered veneer masonry units greater than 2.625 in. (66.7 mm) in depth (Table 3) • Adhered veneer masonry units with weights exceeding 30 lb/ft2 (146 kg/m2) (Table 3) Prior to TMS 402/602-22, any masonry veneer not complying with the prescriptive limitations was required to be designed using the alternative design method, which resembles the current engineered design of adhered veneer conditions1 and the modeling analysis method for anchored veneer. This design method for masonry veneer includes the following: • Units shall comply with the prescriptive requirements or be tested to determine material properties. • Loads shall be distributed through the veneer to the backing using the principles of mechanics. • Masonry veneer assembly shall comply with TMS 602 or be tested to determine design properties. This means engineering analysis can be used to determine the nonprescriptive load path for the given masonry veneer assembly. When the installation of adhered masonry units differs from the prescriptive requirements, the assembly and installation method must be tested to determine the properties to be used with the engineering analysis. For anchored masonry veneer, two engineered design methods are outlined: the tributary area method and the modeling analysis method.1 Regardless of the selected engineered method, the veneer tie properties included in Fig. 8 or the veneer tie manufacturer’s product literature may be used. A veneer tie testing standard
is being developed by ASTM International at the time of this writing. With the publication of this new standard, the masonry industry is facilitating more regular publication of veneer tie capacities and tie assembly stiffnesses for use in engineered design. The tributary area method determines the strength-level force in each veneer tie through the strength-level out-of-plane load on the masonry veneer (pu), the tributary area of the veneer tie (At), and the stiffness of the veneer tie (ktie) using the following equations:1 • 2puAt when ktie ≤ 2,500 lb/in. (438 N/mm) (Equation 1) • 2.5puAt when 2,500 lb/in. (438 N/mm) < ktie ≤ 5,000 lb/in. (876 N/mm) (Equation 2) • 3puAt when 5,000 lb/in. (876 N/mm) < ktie ≤ 8,000 lb/in. (1,400 N/mm) (Equation 3) • 4puAt when ktie > 8,000 lb/in. (1,400 N/mm) (Equation 4) Design strengths in Fig. 8 implicitly include strength reduction factors and can be directly compared with the strength-level forces.1
To convert to allowable stress level forces, pu is replaced with pallow, the allowable wind pressure on the masonry veneer. The tributary area method is limited to anchored veneer with masonry units equal to or less than 5 in. (127 mm) in depth. Veneer ties with lower stiffness allow for a more uniform distribution of lateral forces between the ties. As the stiffness increases, more force is attracted by the veneer tie. For this sample calculation, consider the following scenario: • Cold-formed metal framing backing • Masonry unit depth between 2.625 and 5 in. (66.7 to 127 mm) • Adjustable two-leg pintle veneer tie type (see “plate or prong” type depicted in Fig. 5) • Typical tie spacing of 18 in. (457 mm) by 16 in. (406 mm) or At = 2.00 ft2 (0.186 m2) • pu of 60 lb/ft2 (2.87 kPa) Engineered design is required due to the maximum tributary area exceeding 1.78 ft2 (0.165 m2), which is the enhanced prescriptive limit. Due to the stiffness of the veneer tie type, use Equation 1 and the veneer tie properties in Fig. 7. 2puAt = 2 × 60 lb/ft2 (2.87 kPa) × 2.00 ft2 (0.186 m2) = 240 lb (1,068 N) > 210 lb (934 N), therefore, the solution is not acceptable. Let’s retry using the adjustable slotted veneer tie type. Due to the stiffness of the veneer tie type, use Equation 2. 2.5puAt = 2.5 × 60 lb/ft2 (2.87 kPa) × 2.00 ft2 (0.186 m2) = 300 lb (1,334 N) < 330 lb (1,468 N), therefore, the solution is acceptable. When adjusting the veneer tie type does not reach acceptable results, the tributary area can be reduced by reducing the tie spacing. Alternatively, if large out-of-plane load resistance requires the masonry veneer to be engineered, a wind-tunnel analysis could be performed to potentially reduce the calculated wind-pressure requirements for the components and cladding. POSSIBILITIES OF ENGINEERED MASONRY VENEER Anchored dimension stone veneer is a common exterior cladding system where limestone, sandstone, and other natural stone types are readily available. Dimension stone offers an aesthetic that can define the regional architecture where the stone exists. While some natural stone types exceed the properties of manufactured units, many types have poor
durability characteristics, such as freeze-thaw resistance, or poor bond to modern masonry mortars. Engineering anchored dimension stone veneer, typically through material testing, will confirm whether the available stone products can be attached with veneer ties laid in mortar or whether mechanical anchors, such as kerfstyle anchors, are required to transfer the loads into the backing. While high-wind environments are prescriptively excluded above 75 lb/ft2 (3.59 kPa) for anchored veneer and above 60 lb/ft2 (2.87 kPa) for adhered veneer, hurricane- or tornado-prone regions can benefit greatly from the use of engineered masonry veneer. Manufactured masonry veneer units can offer wind-blown debris or “missile” impact resistance in highwind events. If exterior cladding is installed correctly, the durability of a masonry veneer finish also can protect against one of the leading causes of damage in a hurricane: water infiltration. A building enclosure system protected by masonry veneer will minimize wind-driven rain-related and enclosure impact damage in the veneer area. Engineered masonry veneer removes the dimensional constraints of the prescriptive design method, which provides the designer with more aesthetic possibilities. Large cavity widths can occur with continuous insulation requirements. Any adjustments in unit depth or corbelling pattern further exacerbate veneer cavity depth issues. The prescriptive limitations on cavity width remove compressive buckling as a failure mechanism for the veneer ties. When exceeded, the veneer tie capacity will decrease with increased cavity depth to account for buckling. Working with veneer tie manufacturers to determine ways to counter buckling for the desired cavity depth allows the use of nonprescriptive wall sections. For adhered veneer, units exceeding 30 lb/ft2 (146 kg/m2) or 720 in.2 (0.464 m2) may affect constructability. Adhered veneer unit installation methods are critical to the long-term performance of the adhered masonry veneer assembly. Large units are difficult to install with the uniform pressure to fill the space behind the adhered masonry unit and develop the intended bond strength. As a result, poor installation method is a leading cause of adhered masonry veneer failures. Constructability must be a consideration when developing engineered adhered masonry veneer solutions. Engineered masonry veneer requirements do not necessarily have to exceed prescriptive design method requirements. A powerful application of engineered masonry veneer is optimization of veneers that could be prescriptively designed. Let’s revisit the tributary area method calculation with new conditions to explore optimization. For this sample calculation, consider the following scenario: • Concrete masonry backing • Masonry unit depth between 2.625 and 5 in. (66.7 to 127 mm) • Adjustable two-leg pintle veneer tie type (see wire component of “joint reinforcement” type in Fig. 5) • Typical tie spacing of 16 in. (406 mm) by 16 in. (406 mm) or At = 1.78 ft2 (0.165 m2) • pu of 35 lb/ft2 (1.68 kPa) • Located in Seismic Design Category C Prescriptive design is allowed due to the maximum tributary area not exceeding 2.67 ft2 (0.248 m2), pu < 50 lb/ft2 (2.39 kPa), and location in a low-seismic region. Engineered design is used to optimize the required veneer tie spacing. Due to the stiffness of the veneer tie type, use Equation 1 and the veneer tie properties in Fig. 7. 2puAt = 2 × 35 lb/ft2 (1.68 kPa) × 1.78 ft2 (0.165 m2) = 125 lb (556 N) < 210 lb (934 N), therefore, the solution is acceptable, but there’s room for optimization. Let’s retry using a typical tie spacing of 24 in. (610 mm) by 16 in. (406 mm) (At = 2.67 ft2). Due to the stiffness of the veneer tie type, use Equation 1. 2puAt = 2 × 35 lb/ft2 (1.68 kPa × 2.67 ft2 [0.248 m2] = 187 lb [832 N] < 210 lb [934 N]), therefore, the solution is acceptable. The optimized veneer tie spacing removed 33% of the two leg pintles and layers of joint reinforcement required for the masonry veneer. The cost of the reduced material and labor could be applied elsewhere on the project or used to lower project cost. CONCLUSION Prescriptive design requirements and limitations for masonry veneer are acceptable in many situations. The new engineered design requirements for masonry veneer in TMS 402/602-22 can be used in situations exceeding the prescriptive limitations or to optimize masonry veneer that could be prescriptively designed. Through use of the engineered design provisions, masonry veneer can be used in new applications in a safe and durable manner. The possibilities of engineering masonry veneer are endless. REFERENCES 1. TMS (The Masonry Society), Building Code Requirements and Specification for Masonry Structures, TMS 402/602-22 (Longmont, CO: TMS, 2022). 2. ASTM Subcommittee C15.08, Standard Terminology for Masonry, ASTM C1232-24 (West Conshohocken, PA: ASTM International, 2024). 3. IMI (International Masonry Institute), Base of Wall | Anchored Brick Veneer, CMU Backing, CMU Foundation, May 2, 2019, https://imiweb.org/wp-content/ uploads/01.030.0332-2.pdf. 4. IMI (International Masonry Institute), Base of Wall | Adhered Brick Veneer, CMU Backing, Lath & Scratch Coat, March 26, 2020, https://imiweb.org/wp-content/ uploads/01.070.0301.pdf. 5. ICC (International Code Council), International Building Code (Country Club Hills, IL: ICC, 2024). 6. ASCE (American Society of Civil Engineers), Minimum Design Loads and Associated Criteria for Buildings and Other Structures, ASCE/SEI 7 (Reston, VA: ASCE, 2017). ABOUT THE AUTHOR Robert “Bobby” Chamra is a professional engineer with 12 years of experience focused on structural restoration and building enclosure consulting in existing buildings. Chamra is currently serving as a voting member for The Masonry Society’s TMS 402/602 Building Code Requirements and Specification for Masonry Structures for the 2028 Code Cycle and is the secretary for the Veneer Subcommittee. He has also served as a member of ASTM International Committee C15 Manufactured Masonry Units, Mortars, and Grouts. When not working on the existing built environment, he enjoys spending time with his family, playing golf, gardening, cooking, and eating.
