Masonry system 2 is a rainscreen wall system with steel-framed wall structure and anchored masonry veneer. The typical components of this system, from interior to exterior, are described below in Fig. 2-1. This system is appropriate for many applications including low-, mid-, or high-rise residential or commercial buildings. An example project application of this system is shown in Fig. 2-2 on page 2-2.
As noted in the Introduction, an above-grade wall system controls liquid water, air, heat, and possibly water vapor to function as an e ective 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. 2-3 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. 2-3, the water-shedding surface is located at the anchored masonry veneer, with most water-shedding occurring at the wall face while some water will be stored within the masonry veneer to be released at a later time. The water control layer and the 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 occurs at the interior (warm-in-winter side) of the steel-framed structure.
The water-shedding surface 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 anchored masonry veneer cladding, including both mortar joints and masonry veneer units, is the primary water-shedding surface of the wall system. Additional water-shedding surface components within the wall system include sheet-metal flashings, drip edges, sealant joints, and fenestration systems as shown in the details at the end of this chapter.
To promote water shedding at the masonry veneer face, install mortar joints 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 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. 2-4 on page 2-4. 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.
Masonry veneer ties in this system will penetrate the WRB system and should be sealed as required by the WRB system manufacturer’s installation requirements. Typically, plate ties are bed in a compatible sealant or fluid-applied flashing product or are attached through a self-adhered membrane patch, whereas screw ties with gasketing washers are typically not required to be sealed.
The air barrier system serves as the air control layer. In addition to controlling air, this layer also assists with controlling liquid water, heat, and water vapor.
For this wall system, the air barrier system consists of the same field membrane and many of the components that also serve as the WRB system. 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.
As discussed in the Introduction, the air barrier system must be continuous and fully sealed to resist air flow, whereas the WRB system need not 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 vapor retarder (Class II) 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. 2-1) 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 control layers information is provided in the Thermal Control Layer discussion on page i-30 of the introductory chapter.
The cavity insulation in this system is 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 assembly drying. An example of this insulation is shown in Fig. 2-5 on page 2-6. The semi- rigid properties of the insulation allow it to fit tightly around penetrations such as masonry veneer ties.
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.
Exterior sheathing on this system is typically a gypsum-based product and should be a product resistant to organic growth and moisture. Fiberglass-faced products are commonly used; avoid paper face products.
The anchored masonry veneer is expected to shed most water it is exposed to; however, some moisture is expected to penetrate the cladding and enter the air cavity. This moisture is drained through the air cavity and exits the cladding system where cross-cavity flashings are provided.
In this system, the air cavity between the anchored masonry veneer and the exterior insulation provides drainage behind the cladding and also ventilation when vent ports are provided at the top and bottom of the air cavity. The code- minimum air cavity depth is 1-inch, as required per TMS 402-16;6 however, the risk that mortar droppings will block the air cavity is increased with smaller cavities. A 1-inch cavity may be considered where a strict quality control program is implemented to minimize the risk that mortar droppings will block the cavity; however, a 2-inch air cavity is best practice. Fig. 2-18 demonstrates a typical rainscreen cavity for this system.
Where the air cavity is reduced, which commonly occurs at fenestration rough openings with return brick, a compressible free-draining filler is recommended such as semi-rigid mineral fiber insulation. Mortar should not be packed within these cavities.
The air cavity is ventilated through vents located at the top and bottom coursing of each wall section. Top vents typically occur just below parapet blocking and below intermittent bearing elements such as floor-line shelf angles. Bottom vents, which also serve as weeps and may be referred to as weep/vents, also assist with draining moisture within the air cavity. These weep/vents are typically located just above bearing elements such as loose-lintels, floor line shelf-angles, or foundation walls.
Vents and weep/vents are recommended to be spaced a maximum of 24-inches on-center (e.g., every two to three masonry units) and filled with a cellular or mesh product that fills the head joint of a standard brick unit. It is important that weep fillers extend into the bed joint of the course to facilitate drainage. Avoid weep tubes because they provide far less ventilation and are blocked easily with debris.
Use mortar collection nets at all veneer-bearing locations to prevent mortar from blocking the rainscreen cavity and weeps/vents. Generally, a trapezoidal open-weave, moisture- tolerant net is used.
Sheet-metal components used with this system are reflected throughout the details at the end of this chapter. Cross-cavity sheet-metal components are typically located at all bearing elements such as penetration heads (e.g., window head), floor line shelf-angles, and foundations. These flashings assist with draining the rainscreen cavity and serve to protect fluid-applied or self-adhered flashing membranes that may exist beneath them. Counterflashing 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. Fig. 2-19 on page 2-18 shows an example of sheet-metal components.
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 this system, anchored clay masonry will expand over time as a result of irreversible moisture gain, and mortar joints will shrink slightly over time. In the support system, the steel-framed backup wall will experience little volume change; however, some movement may occur where studs interface with floor and roof lines. To avoid veneer damage, breaks must be provided in the veneer to compensate for differential movement between the cladding and the support wall. Expansion joints must also be provided to allow for overall expansion of the clay masonry veneer; control joints must be provided for shrinkage where concrete masonry veneer units are used.
Differential vertical movement between the structure and the veneer is accommodated with a horizontal gap between the veneer and elements that are directly attached to the wall structure, such as shelf angle supports, parapet blocking, and windows. Either a backer rod and sealant joint or cross-cavity sheet-metal flashing is placed at each horizontal gap. The size and location of joints will vary depending on the expected differential movement between the wall and veneer.
Expansion/shrinkage of the veneer or differential movement between the veneer, penetrations, and different cladding materials is accommodated with vertical joints in the veneer system as shown similar in Fig. 1-18 on page 1-16. Vertical gaps minimize stresses between the veneer and other components to provide crack control for the masonry veneer. Vertical gaps are typically sealed with a backer rod and sealant.
Typical locations of joints for the purposes of 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.
Expansion joints (clay masonry veneer) or control joints (concrete masonry veneer) minimize stresses within the veneer and also between dissimilar materials such as at window jamb to veneer interfaces.
The steel frame walls and concrete floor slabs of this wall system provide the primary structure of this system. It is the responsibility of the Designer of Record to ensure that all structural elements of the backup wall and veneer are designed to meet project-specific loads and local governing building codes. Generic placement of the reinforced elements and supports/ties is demonstrated within the details of this chapter and is provided for diagrammatic purposes only.
Masonry ties (i.e., masonry anchors) are used to connect the veneer to the steel- framed backup wall. They are designed to resist the out-of-plane loads applied to the wall, typically wind and seismic. At the same time, these ties must be flexible to allow the veneer to move in-plane relative to the metal stud–framed wall.
Building codes provide prescriptive requirements for masonry ties secured to concrete or masonry that includes spacing, size, placement, and tie type. These requirements are summarized in Table 2-7 and are based on TMS 402-166 provisions for adjustable ties (i.e., anchors). Use of these prescriptive requirements is limited to masonry veneer assemblies with a weight less than 40 psf, with a cavity depth no more than 65⁄8-inches, and where the ASCE-77 wind velocity pressure (qz) is less than 55 psf (previously wind speed less than 130 mph). Wall assemblies that exceed these criteria require the design professional to evaluate the building loads and materials and rationally design the anchorage system accordingly. The majority of masonry tie manufacturers have empirical testing data available to support the use of their anchorage systems when the cavity depth or loads exceed these criteria.
Prescriptive spacing requirements for anchored masonry veneers are included in Table 2-7 for special requirements for Seismic Design Categories D, E, and F and high-wind zones with velocity pressures (qz) between 40 and 55 psf. These higher seismicity and wind speed areas are common to some parts of the Northwest and are dependent on the geography and building occupancy category. Refer to local building code requirements to ensure seismicity and wind speed criteria are properly evaluated for the building occupancy and site conditions.
Common tie types for reference are shown in Fig. 2-21. For steel-stud framed walls, adjustable ties are required by the code.
To prevent pull-out or push-through of the tie, TMS 402-166 requires ties be embedded a minimum of 11⁄2-inches into the veneer, with at least 5⁄8-inch mortar or grout cover at the outside face. The mortar bed thickness is to be at least twice the thickness of the tie. To prevent excess movement between connecting parts of adjustable tie systems, the clearance between components is limited to a maximum 1⁄16-inch. The vertical o set of adjustable pintle-type ties may not exceed 11⁄4-inches.
TMS 402-166 requires that masonry ties are fastened directly to the steel stud framing through the exterior sheathing with minimum #10 corrosion-resistant screws (0.190-inch shank diameter). They should not be fastened to the sheathing alone. While the code may allow a horizontal anchor spacing up to 32-inches on-center, it is recommended that anchors be spaced horizontally to align with the typical stud spacing, typically 16-inches on-center.
Anchored masonry veneers are supported vertically by the building’s foundation or other structural components such as shelf angles and lintels. Vertical supports are designed to minimize cracking and deflection within the veneer; the support design considers the design loads, material type, moisture control, movement provisions, and constructibility.
For steel stud-framed wall systems, TMS 402-166 requires the anchored masonry veneer to be supported by noncombustible construction; any veneer that exceeds 30 feet in height must be supported at each story above 30 feet. Masonry below 30 feet in height must also be supported at each floor when used in Seismic Design Categories D, E, and F. Best practice for commercial construction is to support the lowest portion of the masonry cladding directly on the concrete foundation wall.
This guide recommends that intermediate supports for masonry are provided with galvanized-steel shelf angles anchored to the structure as needed to limit deflection to less than L/600 as required by TMS 402-16.6 As noted in the Movement Joints sections in this chapter and the introductory chapter, a joint is recommended beneath the angle and closed o from the rainscreen cavity with elastomeric sealant.
Where masonry is supported at openings within the veneer (e.g., windows and doors), shelf angles for larger openings or loose lintels at smaller openings are typically provided. Galvanized-steel loose lintels are recommended except where architectural design dictates reinforced masonry or precast concrete lintels for appearance. Steel angle lintels span the opening; TMS 402-166 requires the lintel bear a minimum of 4-inches onto the adjacent masonry at the jambs of the opening. An example of lintel supports is shown in Fig. 2-22.
Refer to the details at the end of this chapter for detailing of typical support elements.
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 veneer ties, vertical support ledgers and lintels, sheet-metal flashings, and fasteners. This guide includes discussion for common corrosion- resistant materials; however, it is the Designer of Records’ responsibility to appropriate select a level of corrosion resistance for project-specific application/ exposure and the expected longevity of the masonry system.
It is common to provide hot-dipped galvanized carbon steel masonry veneer ties that comply with ASTM A 1538 Class B-2, AISI Type 304, or AISI Type 316 stainless steel per ASTM A580.9 Steel support angles such as shelf angle supports and loose lintels are at minimum hot-dipped galvanized and comply with ASTM A123.10
Best practice is to use sheet-metal flashing components of ASTM A66611 Type 304 or 316 stainless steel, which is nonstaining and resistant to the alkaline content of mortar materials. Whereas 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, this guide recommends the base sheet metal is a minimum G90 hot-dipped galvanized coating in conformance with ASTM A65312 or minimum AZ50 galvalume coating in conformance with ASTM A792.13 Coating the exposed top finish of the sheet metal with an architectural-grade coating conforming to AAMA 62114 is recommended.
Fasteners used with all metal components should be corrosion-resistant, either hot-dipped galvanized steel or stainless steel to match adjacent metal components.
There are several types of anchored masonry veneer products that may be used with this system. Those most typical within the Northwest include facing brick made of clay or shale. Concrete facing brick and concrete masonry units are also used.
For facing brick made from clay or shale, use anchored veneer units that comply with ASTM C21615 and are severe weather (SW) grade. When using concrete facing brick, anchored veneer units are to comply with ASTM C1634.16 Hollow concrete masonry units used for veneer applications are typically 4-inches deep and comply with ASTM C90.17
Mortar designed for the anchored masonry veneer units is to conform to ASTM C270;18 the type selected should be appropriate for the veneer application. Type N mortar is acceptable for most anchored masonry veneer applications. When selecting mortar, the lowest compressive strength (softest) mortar that satisfies the project requirements should be used.
Appropriate product selection of masonry veneer unit and mortar materials is necessary to provide a durable and water-resistive cladding system. The masonry veneer units and mortar joints should also be installed in conformance with industry standard best practices and manufacturer requirements. The specifics of architectural characteristics and structural properties of the masonry veneer units, mortar, and reinforcing 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 at the back of this guide.
Application of a clear water repellent to the anchored 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.
This guide recommends that a sheet-metal flashing is not placed below the precast sill. It can prematurely degrade the mortar bed beneath the precast element.
Exterior insulation should be tightly installed around all penetrations, including masonry ties.
The hot-dipped galvanized-steel standoff shelf angle support reduces the amount of thermal bridging at the floor line when compared to a continuous shelf angle mounted tight to the concrete slab face.
Parapet cavity insulation provides continuity of the thermal control layer at the roof-to-wall transition.
Masonry wall system installation o en precedes roof membrane installation and restricts future access for installation of the roof membrane and flashing components behind the standoff shelf angle support. As a result, installation of a roof membrane prestrip and roof penetration flashing membrane at the concrete wall is needed prior to masonry wall system installation.
Detail 2-H describes a typical rough opening with sill back dam angle. The back dam angle creates a sill pan below the window; intermittent shims below the window promote drainage at the sill and into the rainscreen cavity.
The anchored masonry veneer transitions to Detail 2-D at the outside wall corner. An end dam is recommended where Detail 2-D terminates at the parapet. Refer to Detail 3-K in Chapter 3 for a similar cutaway section at the exterior parapet face.
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 2-3 on page 2-13 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 3-5/8- 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, the system’s thermal performance will need to be determined as a U-factor either through calculation or from tables; however, it may or may not be required to be less than the prescriptive U-factors shown in Table 2-3 on page 2-13.
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., tie type, insulation R-value/inch, etc.) to achieve a target U-factor. Options for thermally optimizing this system, as determined through the modeling results, are also discussed.
Masonry ties and floorline shelf angles penetrate the exterior insulation in this system and create areas of thermal bridging; thermal bridging reduces the system’s actual thermal performance.
Examples of typical anchored masonry veneer ties and a standoff shelf angle support are shown in Fig. 2-6 and Fig. 2-7; the relative thermal bridging that these components can have when penetrating exterior insulation is illustrated in Fig. 2-8 through Fig. 2-13 on page 2-10. Where shown in Fig. 2-9, Fig. 2-11, and Fig. 2-13 the lighter blue thermal gradient color at the attachment describes a warmer temperature than the adjacent darker blue insulation face, which is an indicator of heat loss at the penetration through the insulation. Thermal bridging of the steel studs and concrete slabs are also depicted where the thermal gradient is orange (warmer) at studs and transitions to yellow (cooler) where cavity insulation occurs. 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, masonry veneer ties, and standoff shelf angle support options. A discussion on the modeling performed for this guide is included in the Appendix.
The following are modeling variables specific to this wall system:
– Thermally optimized screw tie with stainless steel barrel and carbon steel fastener. Hooks are either hot-dipped galvanized steel or Type 304 stainless steel.
– Double eye and pintle plate tie (14-gauge). Hooks are either hot-dipped galvanized steel or Type 304 stainless steel to match the tie plate.
Modeling results are shown in Table 2-1, Table 2-2, Fig. 2-14, and Fig. 2-15 (see page 2-12 and page 2-13) for 35/8-inch steel stud walls and Table 2-4, Table 2-5, Fig. 2-16, and Fig. 2-17 (see page 2-14 and page 2-15) for 6-inch steel stud walls demonstrate the system’s effective R-value. Figure references graphically represent the results summarized in each table.
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 Penetrations” such as ties and shelf angles.
As determined from Fig. 2-15, an R-24 target could be provided by one of the scenarios listed below when using R-6/inch exterior insulation. As a result, the tie used can effect the wall thickness without compromising the system’s effective R-value.
– 23⁄4-inches of insulation with a stainless-steel plate tie
– 31⁄4-inches of insulation with a thermally optimized screw tie (with stainless-steel hook)
– 4-inches of insulation with a galvanized-steel plate tie.
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 ASHRAE 90.1,3 COMcheck,4 the appendices of the 2015 WSEC,5 thermal modeling and calculation exercises, or other industry resources.
A pricing summary for this system is provided on Table 2-8 on page 2-27. 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.