The Chapter 4 assembly is a mass wall design approach with a single-wythe concrete masonry unit (CMU) wall structure and core insulation. The components of this assembly, from interior to exterior, are described in Fig. 4-1. Commonly, split-face block is used for this assembly. This assembly is appropriate for low-rise commercial applications; an example application is shown in Fig. 4-2. Benefits and special considerations for this assembly are discussed in Table 4-1.
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. 4-3 illustrates the locations of the critical barrier locations for this assembly. The critical barriers for this assembly are also provided adjacent to each detail at the end of this chapter.
As shown in Fig. 4-3, the WRB and WSS critical barriers occur at/near the CMU wall structure face; the CMU wall structure is also the AB under certain provisions as discussed later in this chapter. The thermal envelope consists of the intermittent foam-insulated core, which may be either resinous foam insulation or loose fill such as perlite. This assembly has no defined VR critical barrier.
The following sections provide more information and discuss best practices for the specific critical barriers of this assembly.
The WSS is a critical barrier that controls water.
The CMU wall itself, along with grout and core insulation provide the 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.
Water repellent admixtures are added to the block and mortar of this assembly and a surface-applied clear-water repellent is also recommended. These repellents—along with other measures such as tooled “V” or concave shape (preferred) mortar joints, sufficient sheet-metal parapet cap design, and other general design recommendations as discussed in the Northwest Concrete Masonry Association (NWCMA) TEK Note on Rain-Resistant Architectural Concrete Masonry—serve to encourage water shed.
When finished, the WSS critical barrier should be free of gaps. Movement joints and joints around fenestrations and penetrations should be continuously sealed with a backer rod and sealant.
The water-resistive barrier is a critical barrier that controls water.
Like the WSS, the CMU wall itself along with grout, mortar, and core insulation provide the WRB critical barrier of this assembly. The addition of water-repellent admixtures within the block and mortar and the use of a surface-applied clear water repellent at the wall face will assist with increasing the water-resistivity of the assembly. Additional measures, such as those discussed in the Water-Shedding Surface (WSS) section of this chapter and addressed within the NWCMA Tek Note on Rain Resistant Architectural Concrete Masonry, increase the water-resistivity of the assembly.
Additional WRB components include flexible flashing membranes at parapet tops, fluid-applied flashings at rough openings, sealant joints, and fenestration systems as shown on the details included at the end of this assembly chapter.
To increase the water-resistivity of this assembly, a vapor-permeable fluid-applied WRB may be applied to the inside face of the assembly, or an elastomeric coating applied to the exterior CMU wall face may be considered. Refer to the introductory chapter for more information on vapor-permeable WRB discussion.
The air barrier is a critical barrier that primarily controls air, heat, and vapor. The AB also controls water, sound, and fire.
The AB system in this assembly is typically satisfied through “deemed to comply” options within the energy codes that govern in the Northwest. Section C402.4 of the 2012 International Energy Conservation Code (IECC), Washington State Energy Code (WSEC), Seattle Energy Code (SEC) and Section 502.4 of the 2014 Oregon Energy Efficiency Specialty Code (OEESC) include “deemed to comply” air barrier considerations including:
Where a fluid-applied AB and WRB membrane is opted for at the interior face of this assembly or an exterior elastomeric coating applied, these membranes along with window rough opening detailing form the AB system.
The thermal envelope is a critical barrier that controls heat and assists with controlling vapor, sound, and fire.
In this wall assembly, the core insulation provides the thermal envelope. At transition details, the thermal envelope also includes insulation at the roof assembly, slab, and foundation elements. Windows and doors that penetrate this wall are part of the thermal envelope.
The CMU wall of 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.
This assembly uses core insulation to meet thermal performance requirements of the energy code. Insulation may be loose fill such as perlite but is commonly an expanding resinous foam-in-place insulation product. Foam-in-place insulation is injected through ports typically drilled through the CMU mortar joints following the construction of the CMU wall and grouting similar to that shown in Fig. 4-4.
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.
This assembly has no vapor retarder and utilizes the IBC Section 1405.3 vapor retarder exception for “construction where moisture or its freezing will not damage the materials.” Note that the partially grouted cells do have some vapor-retarding properties but are not relied upon for control of vapor diffusion.
The CMU wall of this assembly functions as both the WSS and the structure. CMU is a concrete-based product. It, along with the mortar, will shrink over time due to initial drying, temperature fluctuations, and carbonation. Not only will shrinkage movement need to be considered, but differential movement between the CMU structure and other structural elements, deflection, settlement, and various design loads will need to be addressed.
Crack control within the CMU should be considered to increase water-resistivity of this assembly. Material properties and reinforcing methods of the CMU structural wall should be implemented to reduce cracking; however, control joints within the CMU wall should be implemented to provide a plane of weakness to reduce shrinkage stresses and provide continuity of the WSS at these locations. Control joints in CMU can be constructed in a number of ways. Regardless of the method used, a continuous backer rod and sealant joint should be installed at the joint as shown in Fig. 4-5 to assist with water shedding and water penetration resistance.
Refer to the introductory chapter for more information on locating movement joints and sealant joint best practices.
The CMU block 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 grout and reinforced elements are demonstrated within the details of this chapter and are provided for diagrammatic purposes only.
The CMU in this assembly should comply with ASTM C90. Mortar designed for the CMU should conform to ASTM C270 as well as ASTM C1714 when specifying preblended mortar. The mortar type selected should be appropriate for the CMU application; Type S is typically specified. Grout components should comply with ASTM C 476 while aggregate within the grout should comply with ASTM C 404.
Block and mortar should both be specified and provided with a water-repellent admixture as discussed in the Water Repellents section below and the introductory chapter. Refer to the Northwest Concrete Masonry Association for additional information on specifying block, mortar, and grout.
The CMU and mortar joints should be installed in conformance with industry-standard best practices, manufacturer requirements, and guidelines outlined in the NWCMA Tek Note on Rain-Resistant Architectural Concrete Masonry. Appropriate product selection and installation of CMU and mortar materials is necessary to provide a durable and water-resistive cladding system. The specifics of architectural characteristics and structural properties of the block, mortar, grout, and reinforcing should be designed and reviewed by a qualified Designer of Record. Various industry resources are available to assist with CMU wall design and are listed in the Resources section at the back of this guide.
For sheet-metal flashings that are integrated within this assembly (including through-wall flashings and sheet-metal drip flashings), it is best practice to provide components that are manufactured of ASTM A167 Type 304 or 316 stainless steel, which is non-staining and resistant to the alkaline content of mortar and grout 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. The exposed top finish of the sheet metal is recommended to have an architectural-grade coating conforming to AAMA 2605.
Both integral water-repellent admixtures and a surface-applied clear water repellent are included with this assembly and assist with reducing the water absorption of the CMU wall and encourage water-shedding. Water-repellent admixtures should be used both in the CMU and mortar. Admixture within block units should comply with NCMA TEK 19-7 while mortar admixture should comply with ASTM C1384. More discussion on surface-applied clear water repellents is provided in the introductory chapter.
Both CMU and mortar admixtures as well as surface-applied water repellent should have known compatibility performance.
This chapter assembly is typically classified as a “mass” for energy code compliance purposes. Prescriptive energy code compliance values for this assembly are summarized in Table 4-3 and describe:
The 2012 WSEC further clarifies:
A grouted area calculation chart is provided in Table 4-2 to assist with determining the area percentages of grouted cores versus ungrouted cores (e.g., cores available for insulation fill).
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 4-3.
Refer to Fig. i-17 of the introductory chapter, which describes the typical process of navigating energy code compliance strategies and options.
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 on Table 4-4. 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 is valued for the 2015–2016 calendar year.