Masonry system 4 is a mass wall system with a single-wythe concrete masonry unit (CMU) wall structure, often comprised of split face block, and integral insulation. The components of this system, from interior to exterior, are described in Fig. 4-1. This system is appropriate for low-rise commercial applications; an example project application is shown in Fig. 4-2 on page 4-2.
As noted in the Introduction, an above-grade wall system controls liquid water, air, heat, and possibly water vapor to function as an effective and durable environmental separator. Control of these elements, specific to this wall system, is provided by the following control layer systems and/or materials:
For a summary of the relationship between building enclosure loads, control layers, and associated systems and materials, Refer to Fig. i-13 on page i-21 of the introductory chapter.
Fig. 4-3 illustrates the water- shedding surface and control layer locations. The control layers for typical system details are also provided adjacent to each detail at the end of this chapter.
As shown in Fig. 4-3, the water-shedding surface occurs at the CMU wall face. The water control layer occurs at and within the CMU wall structure; the CMU wall structure is also the air control layer under certain provisions as discussed later in this chapter. The thermal control layer consists of the intermittent insulated core. This system has no defined vapor retarder control layer.
The water-shedding surface is a system that serves to reduce 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 CMU block and mortar provide the water-shedding surface of this 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.
Water-repellent admixtures are added to the block and mortar of this system and a surface-applied clear water repellent is also recommended. These repellents serve to encourage water shed—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.1
The water-shedding surface is most effective when free of gaps; therefore, movement joints and joints around fenestrations and penetrations should be continuously sealed with a backer rod and sealant.
The water control layer is a continuous control layer that is designed and installed to act as the innermost boundary against water intrusion. For this system, the CMU block, mortar, and grout (inclusive of any integral water repellents) provide the water control layer.
The water control layer is made continuous with the help of flashing membranes at parapet tops, fluid- applied flashings at fenestration rough openings, sealant joints, and fenestration systems as shown on the details included at the end of this chapter.
To increase the rain penetration resistance of this system, a Class IV vapor permeance fluid applied WRB system may be applied to the inside face of the system, or an elastomeric coating applied to the exterior CMU wall face may also be considered. The WRB system may be a Class III vapor permeance fluid-applied membrane when carefully considered for the project-specific application. Refer to the Elastomeric Coatings discussion on page i-62 for additional information on elastomeric coatings.
The air barrier system provides the air control layer. In addition to controlling air, this layer also assists with controlling liquid water, heat, and water vapor. A general discussion of the air control layer and the air barrier system is provided in the Air Control Layer discussion on page i-26.
The air barrier system for this wall system is typically satisfied through “deemed to comply” options within Section C402.4 of the 2012 International Energy Conservation Code2 (IECC)and Section 502.4 of the 2014 Oregon Energy Efficiency Specialty Code3 (OEESC). These deemed to comply options include:
The 2015 Washington State Energy Code4 (WSEC) and 2015 Seattle Energy Code5 (SEC) do not include deemed-to-comply air barrier materials or systems because the whole building is required to meet air leakage requirements per C402.5. The Code Airtightness Requirements discussion on page i-43 further addresses whole-building air leakage requirements.
Where a fluid-applied WRB system is used at the interior face of this wall system or where an exterior elastomeric coating is applied, these membranes—along with fenestration rough opening membranes—will typically form the air barrier system.
The vapor control layer retards or greatly reduces the flow of water vapor (e.g., vapor barrier) 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.
This system has no vapor retarder and utilizes the IBC Section 1405.36 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 thermal control layer controls heat flow and assists with controlling water vapor.
In this wall system, the core insulation is the primary material that forms the thermal control layer. At transition details, the thermal control layer includes insulation at the roof assembly, slab, and foundation elements. Windows and doors that penetrate this wall are also part of the thermal control layer.
The CMU wall of this system is also a thermal mass; thus, it may provide thermal mass benefits as addressed in the Mass Wall Considerations discussion on page i-42.
This wall system uses core insulation to meet thermal performance requirements of the energy code. Insulation may be loose fill such as perlite but is commonly a resinous, foam-in-place insulation product. Foam-in-place insulation is injected through ports in the CMU mortar joints following the construction of the CMU wall and grouting similar to that shown in Fig. 4-4.
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 due to deflection, settlement, and various design loads will need to be addressed.
Consider crack control within the CMU to increase the rain penetration resistance of this system. Material properties and reinforcing methods of the CMU structural wall should be implemented to reduce cracking; however, control joints within the CMU wall also need to be implemented to provide a plane of weakness to reduce shrinkage stresses and provide continuity of the water-shedding surface 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 is installed at the joint as shown in Fig. 4-5 on page 4-8 to assist with water- shedding and to provide a continuous water control layer.
Refer to the Movement Joints discussion on page i-48 for more information on locating joints and sealant joint best practices.
The CMU block wall of this system provides the primary structure of this system. It is the responsibility of the Designer of Record to ensure that all structural elements of the wall are designed to meet project-specific loads and local governing building codes. Generic placement of the grout, reinforced elements, and supports/anchors are demonstrated within the details of this chapter and are provided for diagrammatic purposes only.
The CMU in this system complies with ASTM C90.10 Mortar designed for the CMU conforms to ASTM C27011 or ASTM C171412 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 47613 while aggregate within the grout should comply with ASTM C 404.14
Block and mortar are both specified with a water-repellent admixture as discussed in the Water Repellents discussion within this chapter. Additionally, refer to the Northwest Concrete Masonry Association (www.nwcma.org) for additional information on specifying block, mortar, and grout.
The CMU and mortar joints of this system 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;1 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 system (including through-wall flashings and sheet-metal drip flashings), it is best practice to provide components that are manufactured of ASTM A66615 Type 304 or 316 stainless steel, which are nonstaining and resistant to the alkaline content of mortar and grout materials. Where stainless steel sheet-metal flashing components are not 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 A65316 or minimum AZ50 galvalume coating in conformance with ASTM A792.17 Coating the exposed top finish of the sheet metal with an architectural-grade coating conforming to AAMA 62118 is recommended.
Both integral water-repellent admixtures and a surface-applied clear water repellent are used in this system and assist with reducing the water absorption of the CMU wall and encourage water shedding. Water-repellent admixtures should be used in both the CMU and the mortar. Admixture within block units should comply with NCMA TEK 19-7,19 while mortar admixture should comply with ASTM C1384.20 More discussion on surface-applied clear water repellents is provided in the Surface-Applied Clear Water Repellents discussion on page i-59.
Both the CMU and mortar admixtures as well as any surface-applied water repellent should have known compatibility performance.
The backer rod and sealant at the window perimeter provides continuity of the water-shedding surface between the CMU wall and storefront window face.
When a sill can is used with the storefront system, a fluid-applied flashing membrane and wept sealant joint at the rough opening should still be used as shown in this detail.
The continuous back dam angle shown allows for perimeter attachment of the storefront window without the need for F-clips or similar anchors, which o en inhibit the air barrier sealant (and thus, the air control layer) at the window perimeter. Project-specific window attachment methods should be confirmed with the window manufacturer during the design phase of the project.
See the next pages for an alternative floor slab detail.
The thermal performance of the concrete floor slab assembly may be improved by providing a thermal insulation break between the floor slab and CMU wall.
When a fluid-applied membrane is applied to the interior face of the single-wythe CMU (to increase the rain penetration resistance and/or to assist with airtightness), as discussed in Water Control Layer on page 4-3, this membrane should extend onto the bottom of the roof structure and should be continuous around anchors.
As shown in Detail 4-H, insulation below the thickened concrete floor slab and exterior of the foundation wall provides additional protection against heat loss at the wall-to-slab interface. The sheet-metal flashing protects the XPS insulation from UV and damage.
Continuous sealant joint at wall-to-slab interface
This wall system is typically classified as a mass above-grade opaque wall system for energy code compliance purposes. Prescriptive energy code compliance values for a mass wall are summarized in Table 4-2 on page 4-8 and describe:
*1) At least 50 percent of cores must be filled with vermiculite or equivalent fill insulation; and
2) the structure encloses one of the following uses: gymnasium, auditorium, church chapel, arena, kennel, manufacturing plant, indoor swimming pool, pump station, water and wastewater treatment facility, storage facility, restroom/concessions, mechanical/electrical structures, storage area, warehouse (storage and retail), motor vehicle service facility).”
Similarly, under the 2015 WSEC4 provisions, the following exception applies, provided the following conditions are met:
*1) At least 50 percent of cores must be filled with vermiculite or equivalent fill insulation; and
2) The building thermal envelope encloses one or more of the following uses: Warehouse (storage and retail), gymnasium, auditorium, church chapel, arena, kennel, manufacturing plant, indoor swimming pool, pump station, water and waste water treatment facility, storage facility, storage area, motor vehicle service facility. Where additional uses not listed (such as o ice, retail, etc.) are contained within the building, the exterior walls that enclose these areas may not utilize this exception and must comply with the appropriate mass wall R-value from Table C402.1.3/U-factor from Table C402.1.4.”
A grouted area calculation chart is provided in Table 4-1 to assist with determining the area percentages of grouted cores versus ungrouted cores (e.g., cores available for insulation fill).
For all energy code compliance strategies except the prescriptive insulation R-value method strategy, this wall system’s U-factor will need to be calculated or determined from tables; however, it may or may not be required to be less than the prescriptive U-factors in Table 4-2 on page 4-8.
The Thermal Performance and Energy Code Compliance discussion on page i-33 and Fig. i-26 on page i-39 describe the typical process of navigating energy code compliance options.
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,4 ASHRAE 90.1,7 COMcheck,8 thermal modeling and calculation exercises, or other industry resources.