Masonry systems 8A and 8B are rainscreen wall systems with wood-framed wall structure and adhered veneer. The adhered veneer may be thin brick, natural stone, or manufactured stone. The components of this system, from interior to exterior, are described in Fig. 8-1 for two options: Option A and Option B. The veneer is applied with either a:
The thick bed method of application, identified as Option A, is most appropriate for low-rise structures. The thin bed method, identified as Option B, is most appropriate for low- to mid-rise structures. Both systems are applicable for residential and commercial applications.
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. 8-3 illustrates the water-shedding surface and control layer locations for this 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. 8-3, the water- shedding surface occurs at the adhered masonry veneer, with most water-shedding occurring at the wall face while some water is stored within the masonry veneer to be released later. The water control layer and air control layer are located exterior of the wall sheathing. The thermal control layer occurs at the framed wall cavity insulation. The vapor control layer is located at the interior (warm-in-winter side) of the wood-framed structure.
The water-shedding surface is a system that reduces the water load on the enclosure. A general discussion 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 the 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 those providing 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 typically has Class IV vapor permeance properties and may be a mechanically attached sheet membrane, a self-adhered sheet membrane, or a fluid-applied system that also functions as the air barrier system; thus, the WRB system is o en referred to as the air barrier and WRB system. An air barrier and WRB system with a Class IV vapor permeance allows this wall system to dry to the exterior. Drying ability to the exterior is not only beneficial during the service life of the building but also helps relieve any construction- related moisture in the wood framing or wood-based sheathing products. A vapor- permeable air barrier and WRB system with mechanically attached field membrane is depicted in the details at the end of this chapter.
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 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 provides the air control layer. In addition to controlling air, this layer 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 many of the components that also 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.
Mechanically attached sheet-applied air barrier and WRB system materials should be attached per manufacturer recommendations to minimize the risk of membrane displacement and damage during wind events. For Option A of this wall system, manufacturer-recommended fasteners may be washer head nails or fasteners. The installation of drainage matrix and cladding components will also assist with securing the air barrier and WRB system in place. For Option B of this wall system, furring strips serve as the mechanical attachment as shown in Fig. 8-4. Note that furring strips should be installed immediately following membrane installation. Where furring strips are not immediately installed, manufacturer- recommended washer head fasteners should be installed.
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.
The vapor control layer of this system is located on the interior (warm-in-winter side) of the wall and is typically at the face of or just behind the interior gypsum board. The vapor retarder for this wall 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 discussion on vapor retarder products.
The thermal control layer controls heat flow and assists with controlling water vapor.
In this wall system, the low-conductivity wood framing and wall cavity insulation form the thermal control layer. At transition details, the thermal control layer also includes parapet cavity insulation and insulation at the roof assembly, slab, and foundation elements. Windows and doors that penetrate this wall system are also part of the thermal control layer. Exterior insulation may also be used with this system, as depicted in Fig. 8-5 on page 8-6, to improve thermal performance of Option B.
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 fiberglass or mineral fiber batt insulation product.
Exterior insulation is typically avoided with Option A due to the difficulty of fastening insulation, drainage matrix, and metal lath materials and the difficulty in supporting final veneer components of this wall system.
Where exterior insulation is desired, Option B of this wall system is more appropriate. The adhered veneer is supported with intermittent cladding support clips and vertical Z-girt furring as shown similarly in Fig. 8-5 and Fig. 8-6. Refer to Chapter 7 for additional discussion on insulation selection, cladding supports, and cladding discussion when exterior insulation is to be used.
Exterior insulation with relatively low vapor permeance properties (e.g., XPS or polyisocyanurate) may be avoided in this wall system because it can limit system drying to the exterior.
Refer to the Insulation Products discussion on page i-30 for information on various considerations.
Low-permeance (Class I, Class II, and sometimes Class III vapor permeance) flashing membranes are commonly used in WRB systems that have vapor-permeable WRB system field membranes. These flashing membranes can be effective on horizontal or low-slope transitions such as window and door rough opening sills or to detail around penetrations and other transitions; however, it is recommended that the use of such membranes is minimized when a vapor-permeable WRB system field membrane is used. This may be achieved by reducing the installation of low-permeance membranes to less than 10 percent of the wall area and by avoiding concentrated areas of low-permeance membranes at wall areas that would otherwise benefit from drying to the exterior (such as in wood-framed systems).
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 261 provisions.
The thermal envelope is a critical barrier that controls heat and assists with controlling vapor, sound, and fire.
In this wall assembly, the cavity insulation provides the thermal envelope. At transition details, the thermal envelope also includes parapet cavity insulation and insulation at the roof assembly, slab, and foundation elements. Windows and doors that penetrate this wall are part of the thermal envelope.
Exterior insulation may also be used with this assembly, as shown in Fig. 8-5, to increase the assembly’s effective thermal performance.
Additional thermal envelope discussion is provided in the Thermal Performance and Energy Code Compliance section of this chapter and the introductory chapter.
The cavity insulation in this assembly is typically a vapor-permeable fiberglass or mineral fiber batt insulation product.
Exterior insulation is not recommended with Option A due to the difficulty of fastening insulation, drainage matrix, and metal lath materials and the difficulty in supporting final veneer components with this system.
Where exterior insulation is desired, Option B of this assembly should be considered. The adhered masonry veneer is supported with a cladding attachment support system made of intermittent clips and Z-girt furring as shown similarly in Fig. 8-5 and Fig. 8-6. Refer to Chapter 7 for additional discussion on insulation selection, cladding attachment supports, and cladding discussion when exterior insulation is to be used.
The VR critical barrier is a layer that retards or greatly reduces (e.g., vapor barrier) the flow of water vapor due to vapor pressure differences across enclosure assemblies.
The VR of this assembly is located on the interior (warm side) and is typically at the face of or just behind the interior gypsum board. The VR for this assembly should comply with Section 1405.3 of the governing International Building Code (IBC). In the Northwest, typical VR products include PVA vapor-retarding primer, asphalt-coated kraft paper, or a polyamide film retarder membrane. These products are further discussed in the introductory chapter.
Although masonry is defined as a noncombustible cladding material, the use of a combustible air and water-resistive barrier or foam plastic insulation within a wall cavity can trigger fire propagation considerations and requirements. Depending on the local jurisdiction, IBC Section 1403.5 regarding vertical and lateral flame propagation as it relates to a combustible water-resistive barrier may require acceptance criteria for NFPA 285. The use of foam plastic insulation within a wall cavity should also be addressed for IBC Chapter 26 provisions.
The exterior sheathing of this system is typically a wood- or gypsum-based product and is designated by structural requirements. Where wood-based products are used, plywood is generally recommended for its moisture tolerance. Where gypsum board is used, a product resistant to organic growth and moisture is recommended. Fiberglass-faced gypsum board products are commonly used; avoid paper face products.
Plywood sheathing may be preferred over gypsum sheathing in system Option A as it provides for a more durable attachment of temporary drainage mat fasteners between framing members.
Some wood preservative treatments may react with certain fastener products; care should be taken to select compatible fasteners and wood preservative treatment.
Adhered masonry veneer with grouted joints is expected to shed most water it is exposed to; however, some moisture is expected to penetrate the cladding and enter the drainage matrix of Option A or the air cavity of Option B. This moisture is either drained through the drainage matrix (see Fig. 8-10) or through the air cavity created by the furring strips of Option B (Fig. 8-13 on page 8-14) and is deflected back to the exterior of the cladding or evaporates by way of ventilation behind the cladding.
For Option A, the drainage cavity is created by the drainage matrix. An example of an entangled-filament drainage matrix with filter fabric facer is shown in Fig. 8-10. A plastic-dimpled drainage matrix may be used as an alternative to the filament type of drainage matrix. This drainage material allows drainage of liquid water and some ventilation. In the Northwest region, a minimum drainage depth of 3/4- inch is o en used; however, 1/2-inch is more common in non-marine areas. A moisture-tolerant filter fabric between the drainage matrix and the mortar bed protects the drainage cavity from mortar collection. This fabric is o en factory-adhered to the drainage matrix and replaces the need for a separate installation of building paper prior to scratch coat application.
For Option B, the air cavity is typically created by 3/4-inch-thick preservative-treated furring strips that align with stud framing as shown in Fig. 8-13. Furring strips allow for more ventilation within the cavity than drainage matrix or mat products. Furring strips should be broken at floor lines and any other location where building movement may occur.
In the Northwest region, the drainage matrix layer or furred air cavity is typically open at the top and bottom to encourage ventilation. When open, it is recommended that the cavity is protected from insects by wrapping the drainage matrix layer perimeter (Option A) or furring
strip terminations (Option B) with insect screen. This approach would commonly be performed at cladding openings, base of walls, and sheet-metal transitions such as at head flashings and cross-cavity flashings.
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. These flashings help drain the rainscreen cavity and protect any air barrier and WRB system components 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.
When Option B is used with exterior insulation, 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.
For both options of this wall system, the wood-framed structure will undergo shrinkage. For Option A, the cement-based scratch and bond coat and mortar joints will shrink. Clay masonry veneer units will expand over time, whereas manufactured concrete veneer products and grout joints between units will shrink. While the reinforcing mesh of Option A will assist with crack control, movement within the veneer and between the veneer and backup wall structure still needs to be accommodated with horizontal and vertical movement joints. Similarly, with Option B, volumetric changes will occur between the veneer and wood-framed wall and must be accommodated. For additional discussion regarding movement of adhered veneers in cement backer board applications (Option B) refer to the Chapter 7 Movement Joints discussion on page 7-14.
For both Options A and B, horizontal gaps within the veneer and cladding and furring strips 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 above and below penetrations (e.g., windows) and below structure projections (e.g., parapet blocking) are also recommended to minimize any stresses on the veneer system. Example locations for an adhered veneer application are shown in Fig. 8-14 on page 8-15.
The location of vertical joints varies throughout the industry and should be confirmed with the veneer unit manufacturer for the project-specific application. This guide recommends locating vertical movement joints throughout the veneer system and considering horizontal-to-vertical placement relationships.
Typical locations of joints for accommodating 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.
For Option A, the masonry veneer is adhered with a bond coat to the mortar scratch and/or brown coats. Metal lath reinforces the mortar and is attached back to the wood-framed structure. The thin masonry veneer should be designed to comply with local building code and TMS 402-166 requirements. The code requires that adhered veneers be applied over concrete or masonry backings and, as such, there are special requirements for installing adhered veneer over wood-framed walls.
In Option A, the metal lath reinforces the mortar scratch coat and minimizes the risk of cracking that may occur due to mortar shrinkage. Metal lath for this wall system is recommended to be a minimum 3.4 lbs/sq yd complying with ASTM C847,7 installed in conformance with ASTM C1780,8 and fastened with a minimum 3/4-inch embedment directly into the wood-framed structure as noted in ASTM 1063.9 Fastener spacing is typically no more than 6-inches on-center vertically. The wood-framed wall itself should be designed to limit the out-of-plane deflection of the wall framing. For thin brick veneer, the Brick Institute of America recommends a maximum deflection of L/360 with a maximum allowable variation of 1/4-inch per 10 feet from plane.10 Fig. 8-15 shows an example of the Option A veneer mock-up.
For the Option B Structural Considerations, refer to the related sections within Chapter 7. As discussed in Chapter 7, where exterior insulation is provided and cladding attachment clips are used, minimizing the cladding support spacing may be considered to limit out-of-plane deflection but should also be balanced with the impact on the system’s effective thermal performance of the wall system. As shown in Fig. 8-16 on page 8-18, smaller cladding support clip spacing is necessary to resist greater wind loads. As clip spacing is reduced, the effective thermal performance of the system is also reduced. Using lower- conductivity clips can reduce the impact that 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 metal lath, sheet-metal flashings, and fasteners such as nails, screws, and staples. Where available, metal components should be manufactured of Type 304 or 316 stainless steel, which are nonstaining and resistant to the alkaline content of mortar materials. Consider minimum G185 hot-dipped galvanized where stainless-steel components may not be available.
Where available, sheet-metal components supporting the veneer or acting as sheet-metal flashings should be AISI Type 304 or 316 stainless steel per ASTM A666,11 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 or economically feasible, G90 or G185 hot-dipped galvanized steel products per ASTM A65312 or minimum AZ50 or AZ55 galvalume-coated sheet steel in conformance with ASTM A79213 may be used but should be carefully considered based on the project’s exposure and expected longevity. Coating the exposed top finish of any sheet metal with an architectural- grade coating conforming to AAMA 62114 is recommended.
Cement backer board used within Option B of this system is exterior-grade water-, mold-, and mildew-resistant, which meets ASTM C132515 Type A (exterior applications) or ANSI 118.9.16 The cement backer board is attached to the continuous vertical furring as required by the backer board manufacturer and project-specific design loads. The attachment method used should be appropriate for the furring and cladding support clip design.
Joints of the cement board are typically staggered and treated with a mesh tape bed in the thinset mortar. Cement backer board product should be installed in conformance with the manufacturer 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.
The crack isolation membrane in Option B is a flexible fluid-applied membrane used in adhered 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 sheathing face of the wood-framed backup wall.
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.
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 C1088.17 Manufactured stone masonry veneer units comply with ASTM C1670.18 For thick bed applications (Option A), the scratch coat complies with ASTM C27019 for site mix applications or ASTM C171420 for preblended mortar and should be Type S or N. Setting bed mortar should also conform to these standards or may conform to ANSI 118.4.21
For applications over cement board substrates, a polymer-modified thinset mortar is recommended. While the brick and manufactured stone veneer industries have not established standards for thinset mortar performance, this guide looks to the tile industry and the American National Standard Institute (ANSI) for the Installation of Ceramic Tile—particularly ANSI A118.15,22 which provides standard specifications for improved performance of modified mortars. This guide recommends that the thinset mortars used in this system demonstrate conformance with the ANSI 118.15.22
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 C1780.23 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.
Applied clear water repellents are recommended for either Option A or Option B applications of this system. Refer to the introductory chapter of this guide for more information on selecting an appropriate clear water repellent and best practice installation guidelines.
Space above and below the sloped cross-cavity sheet-metal flashing is necessary to allow for differential movement between the structure and veneer.
The location of control joints is determined by the project designer and clearly identified in the construction documents on elevations and in details.
Space above and below the sloped cross-cavity sheet-metal flashing is necessary to allow for differential movement between the structure and veneer.
This chapter system is typically classified as a “wood-framed and other” above- grade wall for energy code compliance purposes. Prescriptive energy code compliance values for this system are summarized in Table 8-2 on page 8-13 and describe:
Wood-framed walls are typically constructed with 16-inch on-center stud spacing for standard framing or 24-inches on-center stud spacing for advanced framing methods. Nominal 2×6 framing accommodates up to an R-21 fiberglass or R-23 mineral fiber batt insulation and nominal 2×8 framing up to an R-30 mineral fiber batt insulation. When continuous insulation requirements are to be met, this system uses veneer Option B and will have insulation exterior of the wood frame structure, wall sheathing, and Class IV vapor permeance air barrier and WRB system as discussed in the Chapter 7 system.
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 table values; however, it may or may not be required to be less than the prescriptive U-factors shown in Table 8-2.
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.
When exterior insulation is used with Option B of this wall system, cladding support clips such as intermittent Z-girts or fiberglass standoff clips (as shown in Fig. 8-7 and Fig. 8-9) penetrate the exterior insulation and create areas of thermal bridging (i.e., heat loss). An example of the thermal bridging that a hot-dipped galvanized intermittent Z-girt may have is described by Fig. 8-8, which shows the relative thermal gradient of this system when thermally modeled.
The lighter blue thermal gradient at the clip represents a warmer temperature than the dark blue at the adjacent insulation face—an indicator of isolated heat loss at the penetration through the exterior insulation. This thermal bridging reduces the system’s effective thermal performance.
Three-dimensional thermal modeling demonstrates the effective thermal performance of this wall system for Option A with various types of cavity insulation and for Option B with and without exterior insulation (e.g., Fig. 8-5). A discussion on the modeling performed for this guide is included in the Appendix.
The following are system-specific modeling variables:
– 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 8-1, Fig. 8-11, and Fig. 8-12 (see page 8-12 and page 8-13) and demonstrate the system’s effective R-value under various conditions; Fig. 8-11, and Fig. 8-12 graphically represent Table 8-1 results.
Below is a discussion of the results. For Option B, 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”.
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 in Table 8-3 on page 8-24 (Option A) and Table 8-4 on page 8-25 (Option B). 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. Where Option B may be used with exterior insulation and a cladding attachment support system, refer to the Chapter 7 system Pricing Summary Table 7-5 on page 7-23. Pricing is valid for the 2018 calendar year. Current pricing is also available at www.masonrysystemsguide. com.