Masonry system 7 is a rainscreen wall system with steel-framed wall structure and adhered veneer. The adhered masonry veneer may be thin brick, natural stone, or manufactured stone. The components of this system, from interior to exterior, are shown in Fig. 7-1. This system is appropriate for many applications including low- or mid-rise residential or commercial buildings. An example application of this system is shown in Fig. 7-2 on page 7-2.
As noted in the Introduction, an above-grade wall system controls liquid water, air, heat, and possibly water vapor to function as an effective and durable environmental separator. Control of these elements, specific to this wall system, is provided by the following control layer systems and/or materials:
For a summary of the relationship between building enclosure loads, control layers, and associated systems and materials, Refer to Fig. i-13 on page i-21 of the introductory chapter.
Fig. 7-3 illustrates the water- shedding surface and control layer locations for this wall system. The water-shedding surface and control layers for typical system details are also provided adjacent to each detail at the end of this chapter.
As shown in Fig. 7-3, the water-shedding surface occurs at face of the adhered masonry veneer, with most water-shedding occurring at the wall while some water is stored within the masonry veneer to be released later. The water control layer and air control layer occur at the same location exterior of the wall sheathing. The thermal control layer occurs at the framed wall cavity insulation and exterior insulation. The vapor control layer is located at the interior (warm-in-winter side) of the steel-framed structure.
The water-shedding surface is a system that serves to reduce the water load on the enclosure. A general overview of the water-shedding surface is provided in the Water-Shedding Surface discussion on page i-19.
The adhered veneer cladding—including both grout joints and veneer units—is the primary water-shedding surface of this wall system. Additional water-shedding surface components include sheet-metal flashings and drip edges, sealant joints, and fenestration systems as shown on the details included at the end of this chapter.
To promote water shedding at the masonry cladding, grout joints between veneer units should be installed with a tooled concave (preferred) or “V” shape.
The water-shedding surface is most effective when free of gaps other than for drainage and/or ventilation. Movement joints and joints around fenestrations and penetrations should be continuously sealed with backer rod and sealant or counterflashed with a sheet-metal flashing to deflect wind- driven rain and shed water away from the rainscreen cavity.
The water control layer is a continuous control layer that is designed and installed to act as the innermost boundary against water intrusion. In a rainscreen wall system, the water- resistive barrier (WRB) system is the last line of defense against water intrusion. A general discussion of the WRB system is provided in the Water Control Layer discussion on page i-24.
In this wall system, the WRB system is typically a self-adhered sheet or fluid-applied system that also functions as the air barrier system; thus, the WRB system is often referred to as the air barrier and WRB system. Either a self-adhered sheet or fluid-applied system is depicted in the details at the end of this chapter. An example of a fluid-applied air barrier and WRB system field membrane is shown in Fig. 7-4 on page 7-4. The air barrier and WRB system for this wall system may have:
Physical properties of the WRB system products are discussed in detail in the Water Control Layer discussion on page i-24. Vapor permeability of materials is addressed in the Vapor Control Layer discussion on page i-28.
The air barrier and WRB system must be continuous across the wall system to provide effective water control. In addition to the field membrane, the WRB system includes fluid-applied or self-adhered flashing membranes, sealants, sheet- metal flashings, and penetrations such as windows and doors as shown in the detail drawings that follow this chapter discussion. Where sheet-metal flashing components occur within the system, the back leg of the sheet-metal flashing is shingle-lapped into the WRB system to facilitate drainage at the face of the WRB system and to the exterior of the cladding.
Cladding support clip fasteners in this system penetrate the WRB system and should be sealed as required by the WRB system manufacturer’s installation requirements. Fasteners may be required to be set in sealant, especially at uneven wall planes; however, requirements vary by manufacturer and should be confirmed.
The air barrier system serves to provide the air control layer. In addition to controlling air, this layer also assists with controlling liquid water, heat, and water vapor. A general discussion of the air control layer and the air barrier system is provided in the Air Control Layer discussion on page i-26.
For this wall system, the air barrier system is the same field membrane and most of the components that serve as the WRB system. As discussed in the introductory chapter, the air barrier system must be continuous and fully sealed to resist air flow; whereas, the WRB system is not required to be continuously sealed to be effective, merely shingle-lapped.
The vapor control layer retards or greatly reduces (e.g., vapor barrier) the flow of water vapor due to vapor pressure differences across enclosure assemblies. Unlike the other control layers presented in this guide, the vapor control layer is not always necessary or required to be continuous.
When a Class IV permeance air barrier and WRB system is used within this wall system, typically a Class II vapor retarder is located at the face of or just behind the interior gypsum board. The vapor retarder for this system should comply with Section 1405.3 of the governing International Building Code (IBC).1 In the Northwest, typical vapor retarder products include PVA vapor-retarding primer, asphalt-coated kraft paper, or a polyamide film retarder membrane. Refer to the Vapor Control Layer discussion on page i-28 for additional information.
When a Class I or II permeance air barrier and WRB system is used within this wall system, the WRB system becomes the vapor control layer and a separate vapor control layer (as shown in Fig. 7-1 on page 7-1) is not necessary. Note that in this case, the thermal insulation R-value within the framed wall cavity is recommended by this guide to be 1/2 to 1/3 the total nominal insulation R-value of the wall system.
The thermal control layer controls heat flow and assists with controlling water vapor.
In this wall system, the framed cavity and exterior insulation are the primary materials that form the thermal control layer. At transition details the thermal control layer also includes exterior insulation across floor lines; parapet cavity insulation; and insulation at the roof assembly, slab, and foundation elements. Windows and doors that penetrate this system are also part of the thermal control layer.
Additional thermal insulation information is provided in the Thermal Control Layer discussion on page i-30 of the introductory chapter.
The cavity insulation in this system is typically a fiberglass or mineral fiber batt insulation product.
The exterior insulation in this wall system is typically semi-rigid mineral fiber board insulation (R-4.2/inch)—which is hydrophobic, tolerates moisture, and has free- draining capabilities. Its vapor permeance makes it acceptable for use exterior of a high-permanence air barrier and WRB system without inhibiting drying. An example of this insulation is shown in Fig. 7-4. The semi-rigid properties of the insulation allow it to fit tightly around penetrations such as cladding support clips.
Exterior insulation such as XPS or moisture-resistant polyisocyanurate may be appropriate when a Class I or II permeance air barrier and WRB system is used. Refer to the Insulation Products discussion on page i-30 for a discussion on various insulation types and additional considerations.
Although masonry is defined as a noncombustible cladding material, the use of a combustible air barrier and WRB system or foam plastic insulation within a wall cavity can trigger fire propagation considerations and requirements. Depending on the local jurisdiction, IBC Section 1403.51 regarding vertical and lateral flame propagation as it relates to a combustible WRB system may require acceptance criteria for NFPA 285.2 The use of foam plastic insulation within a wall cavity should also be addressed for IBC Chapter 26 provisions.
The adhered masonry veneer with grouted joints sheds most water it is exposed to; however, some moisture is expected to penetrate the cladding and enter the rainscreen cavity. This moisture is drained through the air cavity (created by the continuous Z-girts that support the cladding) or through the drainable, semi- rigid insulation.
In the Northwest region, the air cavity is typically open at the top and bottom to encourage ventilation. When the air cavity is open, (e.g., at the base of walls and at window head flashings, parapets, and cross-cavity flashings at floor lines), it is recommended that the cavity is covered with a screen to allow ventilation while still protecting the cavity from insects.
Sheet-metal components for this system are reflected throughout the details located at the end of this chapter. Cross-cavity sheet-metal components are located at the head of wall penetrations (e.g., a window head) and at cross-cavity flashing locations similar to that shown in Fig. 7-12. These flashings assist with draining the rainscreen cavity and serve to protect any air barrier and WRB system components located behind them. Counterflashed sheet-metal components assist with water shedding and are typically located at windowsill and parapet top conditions; they protect the cavity from water ingress while allowing ventilation of the air cavity.
Sheet-metal flashing components that penetrate the exterior insulation act as a thermal bridge and degrade the thermal performance of the system; however, they are a necessary element for rainscreen wall system performance.
Refer to the Sheet-Metal Flashing Components discussion on page i-46 for general recommendations on sheet-metal flashing products, including design considerations and materials.
In this system, the masonry units are bonded to a crack isolation membrane over a cement backer board substrate. Clay masonry units will expand over time, whereas concrete-based veneer products and grout joints between units will shrink. Minor movement is expected within the cement backer board and non- metal or intermittent metal-based cladding support clips; however, Z-furring may experience some movement due to temperature changes. The steel-framed backup wall will experience little volume change; however, some movement may occur where studs interface with floor and roof lines. As a result, both horizontal and vertical movement joints are needed to accommodate differential movement between the structure, cladding support system, and veneer components to prevent damage to the veneer or other wall components.
Horizontal gaps within the veneer and cladding support system typically occur at cross-cavity sheet-metal flashing locations that coincide with building floor lines, a common location for building movement. These gaps are typically provided at and should be continuous across all elevations of the building. Gaps are also recommended above and below through-wall penetrations (e.g., windows and those described in the Masonry Veneer Penetrations discussion on page i-54), below structure projections (such as parapet blocking), and where needed to minimize veneer panel sizes. At each horizontal gap there is typically either a compressible backer rod and sealant joint or a cross-cavity sheet-metal flashing. The sizing and location of these joints will vary depending on the expected differential movement between the wall and the veneer.
The locations of vertical joints vary throughout the industry; confirm with the veneer unit manufacturer for the project-specific application. This guide recommends locating vertical movement joints throughout the veneer system and also considering horizontal-to-vertical placement relationships.
Typical joint locations to accommodate movement, drainage, and/or rainscreen cavity ventilation are identified with an asterisk (*) in chapter details. In general, a minimum gap dimension of 3/8-inch is recommended; however, it is the Designer of Record’s responsibility to appropriately locate and size all movement joints.
Refer to the Movement Joints discussion on page i-48 for more information on locating veneer joints and sealant joint best practices.
Adhered veneers rely on adhesion to secure the masonry units and should be designed to comply with local building codes and TMS 402-16.6 The adhered veneer should be designed by the Designer of Record and as described by TMS 402-166 commentary, should consider the adhesion of the veneer units, curvature of the veneer backing, freeze-thaw cycling, water penetration, and air and vapor transmission when necessary.
The code requires that adhered veneers be applied over concrete or masonry backings, and traditionally an adhered veneer was applied directly over these wall types. However, recent code cycles requiring exterior insulation have dictated that adhered veneers over steel stud–framed walls include some insulation exterior of the wall sheathing and WRB system plane.
Per TMS 402-16,6 adhesion between the adhered veneer units and the backer must have a minimum shear strength of 50 psi in accordance with ASTM C482;7 however, significantly higher bond strengths can be achieved with currently available products and may be appropriate for projects within the Northwest region. Adhered veneer units for this system are adhered with a thinset mortar to form a continuous bed that is free of voids. It is best practice to adhere the veneer units of this system with a polymer- modified mortar over a crack isolation membrane and water-resistive cement backer board.
When exterior insulation is required, the masonry veneer is supported by intermittent cladding support clips and continuous vertical Z-girts such as those shown in Fig. 7-13. The spacing of the clips and the sizing of the girts are designed by the Designer of Record to resist building loads and limit out-of-plane deflection of the wall to reduce the likelihood of flexural cracking. Minimizing the cladding support clip spacing may be considered to limit out-of-plane deflection but can impact the effective thermal performance of the system. As shown in Fig. 7-15 on page 7-18, smaller cladding support clip spacing is required to resist greater wind loads. As clip spacing is reduced, the effective thermal performance of the system is also reduced. Using lower-conductivity structural supports can reduce the impact cladding support clips have on the thermal performance.
It is best practice to match the durability and longevity of metal components within this system to that expected of the masonry veneer. Metal components within this system include intermittent Z-girts (when constructed of metal), continuous Z-furring, sheet-metal flashings, and fasteners.
Where available, sheet-metal components supporting the veneer or where acting as sheet-metal flashing components should be manufactured of AISI Type 304 or 316 stainless steel per ASTM A666,8 which are nonstaining, resistant to the alkaline content of mortar materials, and tolerant of the humidity conditions that can exist within the air cavity. Where stainless-steel components may not be available, G90 or G185 hot-dipped galvanized steel products per ASTM A6539 or minimum AZ50 or AZ55 galvalume–coated sheet steel in conformance with ASTM A79210 may be used but should be carefully considered based on the project’s exposure and expected longevity.
Where the use of stainless steel sheet-metal flashing components is not always economically feasible or aesthetically desirable, prefinishing sheet metal may be considered. Where used, the base sheet metal should receive a minimum G90 hot- dipped galvanized coating in conformance with ASTM A6539 or minimum AZ50 galvalume coating in conformance with ASTM A792.10 Coating the exposed top finish of the sheet metal with an architectural-grade coating conforming to AAMA 62111 is recommended.
Fasteners used with metal components should be corrosion-resistant, either hot- dipped galvanized steel or stainless-steel to match adjacent metal components.
Cement backer board used within this system is exterior-grade water-, mold-, and mildew-resistant, which meets ASTM C132512 Type A (exterior applications) or ANSI 118.9.13 The cement backer board is attached to the continuous vertical Z-girts as required by the backer board manufacturer and project-specific design loads. The attachment method used should be appropriate for the Z-furring and intermittent cladding support design.
Joints of the cement board are typically staggered and treated with a mesh tape that is bed into the thinset mortar. Cement backer board product should be installed in conformance with the manufacturer’s installation instructions. The cement backer board should not span joints within the veneer that are expected to accommodate movement similar to that shown in Detail 7-E.
A crack isolation membrane is a flexible fluid-applied membrane used in thin masonry veneer applications where the veneer is adhered to a cement backer board. The crack isolation membrane is applied following installation of the cement backer board and treatment of the board joints as required by the cement backer board manufacturer. This membrane assists with:
Traditionally, this membrane may have been installed to protect the primary structure from moisture exposure. However, in this rainscreen system, the crack isolation membrane is not a replacement for the air and water control layers, which are located on the exterior face of the wall sheathing.
It is best practice to use a crack isolation membrane over cement backer board in adhered masonry veneer applications. Some manufacturers may require this membrane to achieve a warrantable cladding installation. A crack isolation membrane is visible in Fig. 7-16 on page 7-20.
There are several types of adhered veneer unit products that may be used with this system. Those most typical within the Northwest include thin brick made of clay or shale or manufactured stone.
Thin brick used for this system is exterior-grade and complies with ASTM C1088.14 Manufactured stone masonry veneer units comply with ASTM C1670.15
For applications over cement board substrates, a polymer-modified thin set mortar is recommended. While the brick and manufactured stone veneer industries have not established
this guide looks to the tile industry and the Tile Council of North American— particularly ANSI A118.15,16 which provides standard specifications for improved performance of modified mortars. This guide recommends that the thinset mortars used in this chapter’s system demonstrate conformance with the ANSI 118.15.16
Appropriate product selection of masonry veneer unit and thinset mortar materials is necessary to provide a durable and water-resistive cladding system. The veneer units, thinset mortar, and joints should also be installed in conformance with industry-standard best practices and manufacturer requirements and should comply with ASTM C1780.17 The specifics of architectural characteristics and structural properties of the veneer system, including mortar and cladding support systems, should be designed and reviewed by a qualified Designer of Record.
Various industry resources are available to assist with veneer design and are listed in the Resources section.
Application of a clear water repellent to the adhered masonry veneer of this system is common in the Northwest. Refer to the Surface-Applied Clear Water Repellents discussion on page i-59 for more information on selecting an appropriate clear water repellent and for best practice installation guidelines.
The location of control joints is determined by the project designer and clearly identified in the construction documents on elevations and in details.
This wall system is typically classified as a metal-framed (or steel-framed) above- grade wall for energy code compliance purposes. Prescriptive energy code compliance values for this wall system are summarized in Table 7-2 on page 7-11 and describe:
For cavity insulation, steel stud walls are typically constructed with 16-inch on- center stud spacing and can accommodate up to an R-15 batt insulation for 35/8- inch studs or R-21 batt insulation for 6-inch studs. Alternative insulation products may also be used to fill the cavity. Because of its high thermal conductivity, steel framing can reduce the nominal R-value of the stud cavity insulation by approximately 40 to 60%. For this reason, continuous insulation is typically needed to meet prescriptive energy code compliance strategies.
For all energy code compliance strategies except the prescriptive insulation R-value method strategy, this wall system’s U-factor will need to be calculated or determined from tables; however, it may or may not be required to be less than the prescriptive U-factors in Table 7-2.
The Thermal Performance and Energy Code Compliance discussion on page i-33 and Fig. i-26 on page i-39 of the introductory chapter describes the typical process of navigating energy code compliance options. Additionally, the thermal modeling results demonstrated in this chapter may be used to assist with selecting wall system components (e.g. cladding support clip type, insulation R-value/inch, etc.) to achieve a target U-factor. Options for thermally optimizing this assembly, as determined through the modeling results, are also discussed.
Claddings support clips—such as intermittent Z-girts or fiberglass standoff clips as shown in Fig. 7-7—penetrate the exterior insulation in this system and create areas of thermal bridging (i.e., heat loss).
An example of the thermal bridging caused by an intermittent Z-girt is described by Fig. 7-5 and Fig. 7-6, which show the relative thermal gradient of this system when thermally modeled. The lighter blue thermal gradient color at the exterior face of the Z-girt describes a warmer temperature than the adjacent, darker blue insulation face—an indicator of heat loss through the thermal insulation at the penetration. This thermal bridging reduces the system’s effective thermal performance.
Three-dimensional thermal modeling demonstrates this system’s effective thermal performance with various insulation thicknesses, insulation R-values, and cladding support clips/materials. A discussion on the modeling performed for this guide is included in the Appendix.
The following are modeling variables specific to this system:
– Intermittent Z-girts (16-gauge) made of either stainless steel or galvanized steel. Clips are 6-inches tall and spaced at 24-inches on-center vertically, 16-inches on- center horizontally.
– Fiberglass standoff clips spaced at 24-inches on-center vertically and 16-inches on- center horizontally. Both stainless steel and galvanized steel fasteners are considered for the fiberglass standoff clip option.
Modeling results are shown in Table 7-1, Fig. 7-8, and Fig. 7-9 (see page 7-10 and page 7-11) for a 35⁄8-inch steel stud wall and Table 7-3 and Fig. 7-10 and Fig. 7-11 (on page 7-12 and page 7-13) for 6-inch steel stud wall.
Below is a discussion of the results. Where reductions in the system’s effective R-value are discussed, these values are as compared to the system’s effective R-value without clips considered.
– 3-inches (approx.) of R-6/inch insulation with fiberglass clips and stainless-steel screws
– 3.5-inches of R-6/inch insulation with intermittent stainless-steel Z-girts
– 4-inches (approx.) for R-6/inch insulation with fiberglass clips and galvanized steel fasteners or R-4.2/ inch insulation with fiberglass clips and stainless-steel fasteners
Project-specific thermal performance values for an opaque above-grade wall should be used for energy code compliance and determined from a source that is approved by the authority having jurisdiction. Thermal performance sources may include the appendices of the 2015 WSEC,3 ASHRAE 90.1,4 COMcheck,5 thermal modeling and calculation exercises as well as other industry resources.
A pricing summary for this system is provided on Table 7-5 on page 7-23. Pricing demonstrates the relative price per square foot and is based on a 10,000-square- foot wall area with easy drive-up access. Pricing includes all components outboard of the exterior wall sheathing and provides no evaluation for interior finishes (including vapor retarder), framing/sheathing, or cavity insulation. Pricing is valid for the 2018 calendar year. Current pricing is also available at www. masonrysystemsguide.com.