The Chapter 1 assembly is a rainscreen design approach with CMU or concrete wall structure and anchored masonry veneer. The components of this assembly, from interior to exterior, are described in Fig. 1-1. This assembly is appropriate for many applications including low-, mid-, or high-rise residential or commercial structures. An example application of this assembly is shown in Fig. 1-2. Benefits and special considerations for this assembly are discussed in the Comparison Matrix.
This assembly with a concrete backup wall alternate is also depicted in Fig. 1-3 and contains similar typical components to that described in Fig. 1-1.
As noted in the Introduction, an above-grade wall assembly should provide control of water, air, heat, vapor, sound, and fire to serve as an effective and durable environmental separator. Control of these elements is provided by critical barriers such as a water-shedding surface (WSS), water-resistive barrier (WRB), air barrier system (AB), thermal envelope, and vapor retarder (VR). Refer to Fig. i-8 of the introductory chapter for a list of primary building enclosure control functions and associated critical barriers.
Fig. 1-4 illustrates the critical barrier locations for this assembly when a CMU backup wall is used. The critical barriers for typical Chapter 1 assembly CMU details are also provided adjacent to each detail at the end of this chapter.
As shown in Fig. 1-4, the WSS critical barrier occurs 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 WRB, AB, and VR critical barriers are all depicted at the same location at the exterior face of the CMU wall structure. As a result, a single membrane is used to serve as the WRB and AB (and may serve as the VR); this membrane is commonly referred to in this chapter as the air and water-resistive barrier (AB/WRB). The thermal envelope barrier includes the exterior insulation between the wall structure and masonry veneer.
The following sections provide more information and discuss best practices for the specific critical barriers of this assembly.
The WSS is a critical barrier which controls water.
The anchored masonry veneer cladding, including both mortar joints and masonry veneer units, is the primary WSS of this assembly. Additional components include sheet-metal flashings and drip edges, sealant joints, and fenestration systems as shown on the details included at the end of this assembly chapter.
To promote water shedding at the masonry veneer face, joints between masonry units should be appropriately installed with a tooled concave (preferred) or “V” shape.
When finished, the WSS critical barrier should be free of gaps except where 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 WRB is a critical barrier that controls water.
In this assembly, the WRB critical barrier is primarily a self-adhered sheet or fluid-applied membrane that also functions as the AB system and may function as a VR; thus, it referred to as the AB/WRB membrane. A fluid-applied or self-adhered sheet AB/WRB field membrane are depicted in the details at the end of this chapter. An example of a fluid-applied AB/WRB membrane is shown in Fig. 1-5 on a concrete backup wall alternate. This membrane may be either a vapor-permeable or vapor-impermeable product because it is located interior of the assembly’s thermal envelope. Physical properties, such as vapor permeability of WRB products are discussed in detail in the Water-Resistive Barrier (WRB) section of the Introduction.
The AB/WRB layer must be continuous across the wall face to serve as an effective critical barrier. In addition to the AB/WRB field membrane, the WRB critical barrier also includes fluid-applied or flexible flashing membranes, sealants, sheet-metal flashings, and interfaces with fenestration systems (e.g., windows and doors) as shown in the detail drawings that follow this chapter discussion. Where sheet-metal flashing components occur, the back leg of the sheet-metal flashing is lapped into the AB/WRB field membrane to encourage water at the WRB layer to drain toward the building exterior.
Masonry veneer ties in this assembly will penetrate the AB/WRB critical barrier and should be detailed based on the membrane 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 typically do not require any detailing at the WRB plane.
Where a ladder eye-wire masonry veneer attachment method is used, a fluid-applied AB/WRB membrane is recommended; each wire penetration through the AB/WRB membrane should be sealed with a sealant or fluid-applied flashing material as recommended by the fluid-applied AB/WRB manufacturer.
The AB system is a critical barrier that primarily controls air, heat, and vapor. The AB system also controls water, sounds, and fire.
In this assembly, the AB system critical barrier is the same self-adhered sheet or fluid-applied field membrane that also serves as the WRB critical barrier. The components described in the above Water-Resistive Barrier (WRB) section are also part of the AB layer, except sheet-metal flashings.
A mechanically attached air and water‑resistive barrier membrane (AB/WRB) may be used for this assembly where recommended by the manufacturer for installation over a CMU or concrete wall substrate.
The thermal envelope is a critical barrier that controls heat and assists with controlling vapor, sound, and fire.
In this wall assembly, the exterior insulation provides the thermal envelope. At transition details, the thermal envelope includes exterior insulation across bond beams, peripheral floor lines, and roof assembly insulation as well as slab and foundation insulation. Windows and doors that penetrate this wall are also part of the thermal envelope.
Exterior insulation provides the following benefits:
The CMU (or concrete) in this assembly is also a thermal mass; thus, may provide thermal mass benefits as discussed in the introductory chapter.
Additional thermal envelope discussion is provided in the Thermal Performance and Energy Code Compliance section of this chapter and the introductory chapter.
For this assembly’s exterior insulation, semi-rigid mineral fiber board insulation or moisture-tolerant rigid board insulation products (e.g., polyisocyanurate or XPS as shown in Fig. 1-6) may be used. Refer to the Introduction for a discussion on various insulation types and considerations.
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. Unlike the other critical barriers presented in this guide, the VR is not always necessary or required to be continuous.
For this assembly, a VR is not necessary. The risk of condensation development or damage to the structure due to outward vapor drive and condensation is unlikely due to all of the assembly’s insulation being located exterior of the wall structure and the AB/WRB barrier.
Note that Fig. 1-4 identifies the VR at the exterior face of the CMU wall. This represents the exterior-most plane of the CMU wall structure, which has some vapor resistance. It would also represent the location of a VR if a relatively impermeable AB/WRB membrane is used.
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 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 rainscreen cavity. This moisture is drained through the rainscreen cavity and exits the rainscreen system where cross-cavity flashings are provided.
In this assembly, a 2-inch deep rainscreen cavity between the anchored masonry veneer and exterior insulation should be provided to encourage drainage and ventilation. At minimum, a 1-inch gap may be provided and is the minimum code-allowable depth. However, the risk that mortar droppings will reduce the drainage and ventilation within the rainscreen cavity is increased with smaller cavities. A 1-inch cavity should only be provided where a strict quality control program is implemented to ensure mortar droppings do not block the cavity. Fig. 1-16 demonstrates a typical rainscreen cavity for this assembly.
Where the rainscreen cavity is reduced, such as at window rough openings with return brick, a compressible free-draining filler is recommended; semi-rigid mineral fiber insulation may be used. In any case, mortar should not be packed within these cavities.
The rainscreen 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 also serve as weeps to assist with drainage of the rainscreen cavity. These vents/weeps are typically located just above bearing elements such as loose-lintels, floor line shelf-angles or foundation walls.
Vents and weeps 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. Weep tubes should not be used at vent/weep locations because they provide far less ventilation and are blocked easily with debris.
Mortar collection nets are recommended at all veneer-bearing locations to prevent mortar from blocking the rainscreen cavity and vents/weeps. It is best practice to use a trapezoidal-shaped open-weave, moisture-tolerant net.
Sheet-metal components for this assembly are reflected throughout the details located at the end of this chapter. Cross-cavity sheet-metal components are typically located at all bearing elements such as the head of a penetration (e.g., window head), floor line shelf-angles, and foundation. These flashings assist with draining the rainscreen cavity and also serve to protect fluid-applied or flexible flashing membranes, which may exist beneath them. Counterflashing sheet-metal components assist only with watershedding and are typically located at window sill and parapet top conditions; they protect the cavity from water ingress while still allowing for cavity ventilation.
Refer to the Introduction Chapter of this guide for general recommendations on sheet-metal flashing products, including design considerations and materials.
For this assembly, anchored clay masonry will expand over time as a result of irreversible moisture gain, and the mortar joints will shrink slightly overtime. In the CMU wall structure, shrinkage will occur over time due to initial drying and carbonation. To avoid damage to the veneer or other wall components, differential movement between the wall structure and veneer must be considered. Expansion joints also must 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 movement between the wall structure and veneer is accommodated with a horizontal gap between the veneer and elements that are directly attached to the wall structure, such as shelf angles, parapet blocking, and windows. Locations where this gap should occur are indicated with an asterisk (*) in the details at the end of this chapter. At each horizontal gap, either a backer rod and sealant joint or cross-cavity sheet-metal flashing should be placed. The sizing and location of joints will vary depending on the expected differential movement between the wall and veneer. It is the Designer of Record’s responsibility to appropriately locate and size each joint. In general, a minimum gap dimension of 3/8-inch should be provided.
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. 1-17. Vertical gaps minimize stresses between the veneer and other components to provide crack control for the masonry veneer. All vertical gaps should be sealed with a backer rod and sealant. It is the Designer of Record’s responsibility to appropriately locate and size each joint. In general, a minimum gap dimension of 3/8-inch should be provided.
Refer to the Introduction Chapter of this guide 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 CMU block (or concrete) wall of this assembly provides the primary structure of this assembly. It is the responsibility of the Designer of Record to ensure that all structural elements are designed to meet project-specific loads and local governing building codes. Generic placement of the grout and reinforced elements are demonstrated within the details of this chapter and are provided for diagrammatical purposes only.
Masonry ties are used to connect the veneer to the masonry (or concrete) wall structure. They are designed to resist the out-of-plane loads applied to the wall, typically wind and seismic. At the same time, ties must be flexible to allow the veneer to move in-plane relative to the backing wall.
Building codes provide prescriptive requirements for masonry ties secured to concrete or masonry that include spacing, size, placement, and tie type. These requirements are summarized in Table 1-4 and are based on ACI-530 provisions. The use of these prescriptive requirements are limited to masonry veneer assemblies with a weight less than 40 psf, a cavity depth no more than 4.5 inches , and where the ASCE-7 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 1-4 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.
Typical tie types for reference are shown in Fig. 1-18. For masonry and concrete walls, adjustable ties are required and may include embedded wire or joint reinforcement or surface-mounted connectors with adjustable ties. Based on local best practices, double eye and pintle type ties (whether a plate or screw type) are preferred. Double eye and pintle ties are available from a number of manufacturers in a variety of sizes to meet project requirements in the Northwest. Test data are typically available to justify the use of these tie types when an engineered tie system is required rather than prescriptive compliance.
Embedded joint reinforcement ties may also be used with masonry backup walls. The joint reinforcement includes two eye-wires that protrude out from the face of the backup wall at a nominal spacing, extending through the exterior insulation. This tie type is common with CMU backup walls, but offers less adjustability and additional coordination for successful placement and use.
Adjustable triangular wire ties are acceptable but may not be preferred by installers because the vertical tie orientation can complicate the exterior insulation installation process by requiring vertical orientation of insulation boards. Corrugated masonry ties and non-adjustable surface-mounted ties are not allowed by ACI-530 for this assembly.
To prevent pull-out or push-through of the tie, embed each tie a minimum of 1-1/2 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, limit clearance between components to less than 1/16-inch. The vertical offset of adjustable pintle-type ties may not exceed 1-1/4 inches.
When using surface-mounted ties, fasten them directly to the concrete or masonry framing with hammer-driven, expanding pin fasteners with a stainless steel pin and a zinc-aluminum (Zamac) alloy jacket. Fasteners should be sized to provide pull-out capacity equal to or greater than the masonry tie itself.
Ties should be hot-dipped galvanized carbon steel that complies with ASTM A 153 Class B-2 or stainless steel that complies with AISI Type 304 or 316. Fasteners used with these ties should be corrosion-resistant, either galvanized steel or stainless steel, to match the tie selection.
It is important to also recognize that recent energy code changes may require insulation thickness to exceed 3.5 inches. In such cases, the wall cavity will exceed 4.5 inches (when including a minimum 1-inch air space), which will trigger the code requirement for an engineered anchor system, rather than prescriptive compliance.
Anchored masonry veneers are supported vertically by the building’s foundation or other structural components. There are generally three methods of supporting masonry veneers:
An example of both structural bearing and loose lintel vertical support elements are shown in Fig. 1-19.
While the function of each support method is different, they each must be designed to eliminate the possibility of cracking and deflection within the veneer. Selection of the appropriate support method should consider the design loads, material type, moisture control, movement provisions, and constructability.
For concrete and masonry backings, anchored masonry veneer should be supported vertically by noncombustible construction. Best practice for concrete- and masonry-backed veneers is to support the lowest portion of the masonry cladding directly on the concrete foundation.
The code does not place any height restrictions or requirements for intermediate support of masonry with concrete or masonry backings. However, the designer should provide intermediate support to accommodate movement and prevent cracking of the veneer associated with differential movement of the veneer, ties, building structure, and other building components. It is recommended that intermediate supports are provided every 20 feet or every 2 floors, whichever is greater, for structural considerations and to facilitate drainage and ventilation of the rainscreen cavity.
Intermediate supports for masonry should be provided with galvanized steel shelf angles, anchored directly at the floor slab level. The floor slab design should be sufficient to limit floor deflection to less than L/600 or 0.3 inches, whichever is less. As noted in the Movement Joints sections of this chapter and the Introduction Chapter, a joint should be provided beneath the angle and sealed with elastomeric sealant.
Masonry cladding must also be supported at openings within the veneer, such as at windows and doors. This may be done with shelf angles, for larger openings, or with loose lintels at smaller openings. Galvanized steel loose lintels are typically used except where architectural design dictates the use of reinforced masonry or precast concrete lintels for appearance. Steel angle lintels should span across the opening and bear a minimum of 6 inches onto the adjacent masonry at the jambs of the opening.
Refer to the details at the end of this chapter for detailing of typical support elements.
Based on local best practices, use double eye and pintle type ties, whether a plate or screw type.
To avoid premature cladding replacement, the durability and longevity of metal components within this assembly should match that expected of the masonry veneer cladding system. Metal components within this assembly include veneer ties, vertical support ledgers and lintels, sheet-metal flashings, and fasteners.
Veneer ties should be hot-dipped galvanized carbon steel that complies with ASTM A 153 Class B-2 or stainless steel that complies with AISI Type 304 or 316 such as that shown in Fig. 1-20. Steel support angles such as ledger angles and lintels should be a minimum G185 hot-dipped galvanized. Sheet-metal flashing components should be manufactured of ASTM A167 Type 304 or 316 stainless steel, which is non-staining 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, the base sheet metal should receive a minimum G90 hot-dipped galvanized coating in conformance with ASTM A653 or minimum AZ50 galvalume coating in conformance with ASTM A792. It is recommended that the exposed top finish of the sheet metal be coated with an architectural-grade coating conforming to AAMA 2605.
Fasteners used with all metal components should be corrosion-resistant, either galvanized steel or stainless steel.
There are several types of anchored masonry veneer products that may be used with this assembly. Those most typical within the Northwest include facing brick made of clay or shale. Concrete facing brick and concrete masonry units are also used.
When using facing brick made from clay or shale, anchored veneer units should comply with ASTM C216 and be severe weather (SW) grade. When using concrete facing brick, anchored veneer units should comply with ASTM C1634. Hollow concrete masonry units used for veneer applications are typically 4-inches deep and should comply with ASTM C90.
Mortar designed for the anchored masonry veneer units should conform to ASTM C270, and 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.
A clear water repellent should be applied to the anchored masonry veneer of this assembly. Refer to the Introduction Chapter for more information on selecting an appropriate clear water repellent and for best practice installation guidelines.
A significant thermal bridge occurs at the foundation element. The insulation between the concrete floor slab and concrete foundation wall is typically referred to as a thermal break and helps reduce the amount of heat loss at the floor slab perimeter and concrete foundation element.
Vents/weeps at the wall base provide assistance to drain the rainscreen cavity and also provide ventilation. The mortar collection mesh helps keep vents/weeps clear of mortar droppings.
This assembly is typically classified as a “mass” above-grade wall for energy code compliance purposes. Prescriptive energy code compliance values for this assembly are summarized in Table 1-3 and describe:
When a non-prescriptive compliance option (e.g., a trade-off strategy or whole-building modeling strategy) is used for energy code compliance, this assembly’s effective thermal performance will need to be calculated; however, it may or may not be required to meet the prescriptive values shown in Table 1-3.
Fig. i-17 of the introductory chapter describes the typical process of navigating energy code compliance strategies and options. Thermal modeling results demonstrated within this chapter may be used to assist with estimating insulation and tie selection to achieve a project specific wall assembly thermal performance value. Options for thermally optimizing this assembly, as determined through the modeling results, are also provided.
Masonry ties and floorline shelf angles penetrate the exterior insulation in this assembly and create areas of thermal bridging; thermal bridging reduces the assembly’s actual thermal performance.
Examples of thermal bridging are described by Fig. 1-8 through Fig. 1-13. Where shown in Fig. 1-9, Fig. 1-11, and Fig. 1-13, the lighter blue thermal gradient color at the attachment locations describes a warmer temperature than the adjacent darker blue insulation face—an indicator of heat loss at the penetration through the insulation. This thermal bridging reduces the assembly’s effective thermal performance.
Three-dimensional thermal modeling demonstrates this assembly’s effective thermal performance with various insulation thicknesses, insulation R-values, masonry veneer anchors, and standoff shelf angle options. A discussion on the modeling performed for this guide is included in the Introduction Chapter and the Appendix.
The following are modeling variables specific to this assembly—CMU wall with anchored masonry veneer:
The results of this modeling are shown in Table 1-2, Fig. 1-14, and Fig. 1-15 and demonstrate the assembly effective R-value under various conditions; Fig. 1-14, and Fig. 1-15 are graphical representations of the results summarized in Table 1-2. Discussion of these results is provided below and key points for thermally optimizing this assembly are italicized in boldface.
Project-specific thermal performance values for the opaque above-grade wall assembly of this chapter should be used for energy code compliance and should be determined from a source that is approved by the local governing jurisdiction. Sources may include the Appendices of the WSEC and SEC, ASHRAE 90.1, COMcheck, thermal modeling, or other industry resources.
A pricing analysis for this assembly is provided in Table 1-5 of this chapter. 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 CMU wall structure and provides no evaluation for interior finishes or CMU wall structure. Pricing for this assembly is for a CMU wall backup wall structure; a concrete backup wall structure is expected to be comparable.
Pricing is valued for the 2015–2016 calendar year.