Masonry has been used successfully in building construction in the Northwest region (Washington, Oregon, and Idaho) for many decades as both the primary structural system and as a cladding. Masonry has withstood the test of time not only because of its natural resistance to fire, water, impact, and organic growth, but also because of its design versatility.
Historically, structural mass masonry wall assemblies were commonplace, primarily due to their superior fire resistance, durability, and weatherability. Over time, such assemblies have given way to alternate structural framing materials. By definition, mass structures inherently address the many above-grade wall functions, including control of water, air, heat, sound, and fire. Replacing the mass structure increases the complexity of the wall design as follows:
Traditional decorative and durable cornice and cornerstone elements and built-in drip edges at strategic locations were typical of mass masonry structures and responsible for deflecting much of the water cascading down the face of these buildings. These design elements have been either eliminated or traded for more modularized and economized veneer units that, while reminiscent of historic mass masonry construction detailing, do not have the same water-deflecting characteristics. Fortunately, most veneer assemblies are able to accommodate the added moisture ingress due to a concealed drainage cavity and flashings. The result is a similar material aesthetic, fire resistivity, and durability, yet a flatter and simpler appearance lacking the intrinsic ability to deflect water away from the masonry-clad wall face and away from areas most sensitive to water entry, e.g., wall penetrations such as vents, windows, and doors.
Though the evolution of the above-grade wall design has led to more complex overall assemblies, product selection, and code compliance than in previous years, it has also demonstrated the durable and accommodating nature of modern above-grade wall assemblies to the local climate conditions of the Northwest region.
As a result, the focus of this guide is to provide comprehensive design and construction detailing information for 8 primary above‑grade wall assembly options successfully used in the Northwest climate that are composed of clay or concrete masonry as an adhered or anchored veneer or single-wythe CMU wall application. The focus for each assembly is to clarify the overall above-grade wall building enclosure design as it relates to managing heat, air, and moisture (both liquid water and vapor) transfer between the interior environment and exterior environment and to demonstrate the constructibility of these structures to ensure long-term durability. Cladding considerations including attachment and installation methods are also addressed. Each assembly within this guide is addressed specific to the Northwest region, including Washington, Oregon, and Idaho and considers local climate, codes, and building preferences and practices.
This introductory chapter showcases the 8 primary above-grade wall assemblies that are the focus of this guide. This introduction also contains technical references and supporting information for general topics that apply to the featured above-grade wall assemblies.
Each subsequent chapter is dedicated to one of the primary above-grade wall assemblies and provides assembly-specific discussion, guidance, photos, and/or diagrammatic illustrations. Two- and three-dimensional details and cutaway wall sections are provided at the end of each chapter, summarizing the chapter content and illustrating its use in real-world applications.
The information presented within this guide is not meant to be exhaustive of all assembly variations, product performance properties, or detailing approaches but rather represents a selection of the best practices and preferences used in the Northwest region.
Chapter 1: CMU (or Concrete Alternate) Wall with Anchored Masonry Veneer
Chapter 2: Steel-Framed Wall with Anchored Masonry Veneer
Chapter 3: Wood-Framed Wall with Anchored Masonry Veneer
Chapter 4: Integrally Insulated CMU Wall
Chapter 5: Interior-Insulated CMU Wall
Chapter 6: CMU Wall with Adhered Masonry Veneer
Chapter 7: Steel-Framed Wall with Adhered Masonry Veneer
Chapter 8: Wood-Framed Wall with Adhered Masonry Veneer (Thick or Thin Bed Method)
The Table i-1 Assembly Comparison Matrix is provided to assist designers with assembly selection. Comparison categories are those generally considered for both commercial and/or residential applications and include:
A pricing analysis is provided for each assembly within this guide and demonstrates the relative price per square foot. Pricing is for components outboard of the wall sheathing for framed or CMU backup wall assemblies. For exterior-exposed CMU wall systems, pricing includes all components except interior finishes and steel framing (where it occurs). Pricing is based on a 10,000- square-foot wall area and is valued for the 2015–2016 calendar year.
Overall pricing is included within the Assembly Comparison Matrix beginning. A pricing breakdown and additional related discussion is included in a summary table at the end of each assembly chapter.
Available online are downloadable digital versions of two- and three-dimensional assembly details and cutaway sections as well as sample project specifications. Ongoing additions to references and resources included within this guide can also be accessed.
The remaining sections within this introduction serve as a reference for topics consistent among many of the chapter assemblies. These topics include building enclosure system and loads; identification of building enclosure control functions and critical barriers; assembly design approaches; thermal performance and energy code compliance; sheet-metal components; movement joints; as well as cleaning, repellents, and coatings.
The building enclosure (building envelope) is a system of materials, components, and assemblies physically separating the interior environment from the exterior environment(s). As an environmental separator, the building enclosure can be grouped into three subcategories: support, control, and finish. Support satisfies structural requirements whereas finish satisfies interior and exterior aesthetics.
As an environmental separator, the building enclosure controls heat, air, and moisture transfer and, along with the heating and ventilation systems, helps maintain a comfortable and healthy indoor environment.
The elements of the building enclosure include roofs, above- and below-grade walls, windows, doors, skylights, exposed floors, the basement/slab-on-grade floor, and all of the interfaces and details in between. Typical building enclosure elements are depicted in Fig. i-4. As the focus of this guide is specific to the 8 primary assemblies described in the previous sections, only design considerations for above-grade walls are addressed here. Where appropriate, detailing considerations are also discussed and included for roof, floor-line, and foundation assembly transitions as well as fenestration openings within the above-grade wall.
Over the lifespan of a building, the building enclosure will be subjected to a wide range of interior and exterior environmental loads. Exterior environmental loads include solar radiation, rain, snow, ice, hail, vapor condensation, wind, temperature, relative humidity, insects, pests, and fungi. Interior environmental loads include temperature, relative humidity, and vapor condensation as well as water and water vapor associated with human activities and potential defects in appliances, sprinklers, and interior plumbing.
The impact of rain on and flow over the exterior surface of the building—as well as differences in temperature, air water vapor content, and air pressures between the interior and exterior environments—creates the most critical loads acting on the enclosure. Fire, smoke, and noise separation must also be considered; however, they are beyond the scope of this guide.
The location or climate zone in which the building is constructed dictates the magnitude and duration of these environmental loads on the building enclosure. Every climate zone carries unique design, construction, and maintenance considerations. As depicted in Fig. i-5 and defined by ASHRAE 90.1, three climate zones exist in the Northwest: Zone 5, Zone 6, and Marine Zone 4. These climate zones impose a wide range of environmental loads, including rainfall as shown in Fig. i-6 and Fig. i-7. In the Northwest, rainfall loads span from areas of significant precipitation and cooler temperatures near the western Washington peninsula, the Oregon coast, and the higher elevations of Idaho; more extreme temperatures occur both in winter and summer months in dryer areas in eastern Washington and Oregon and southern Idaho.
A primary function of the building enclosure is to control (or rather appropriately manage) environmental loads. Various materials are used within enclosure assemblies and details to perform different control functions depending on their material properties and placement. The following control functions are typically considered: water (precipitation and ground), water vapor, air, heat, sound, fire, light, and contaminants. The interior and exterior finish can also be considered as part of the control function. For the purpose of this guide, the primary control functions of water, air, heat, and vapor are addressed in greater detail. Consideration of sound, fire, light, and contaminants may be related to the concepts discussed within this guide but are not covered in detail.
Applying the concept of control functions, the term critical barrier is commonly used to refer to materials and components that together perform an important function within the building enclosure. A critical barrier must be continuous for the enclosure to perform as designed. It has become common and referenced within building codes to define specific critical barriers within an enclosure assembly, such as a vapor retarder/barrier or an air barrier. Fig. i-8 depicts the link between the concept of control functions and the associated critical barrier. Fig. i-8 also describes primary and secondary relationships.
The use of critical barrier concepts to evaluate assemblies and details is consistent with industry best practices. The concepts are useful to assess specific assemblies and details being considered for a project. The application of the critical barrier concept will help all parties better understand the role and importance or functions of certain materials and details. As a result, the critical barriers of water-shedding surface (WSS), water-resistive barrier (WRB), air barrier (AB), thermal envelope (e.g. thermal insulation), and vapor retarder/barrier (VR) are demonstrated for each chapter assembly and their respective two-dimensional details throughout this guide. Building form and features are also important concepts for controlling water and are only addressed in this introductory chapter to provide general design guidance.
Throughout this guide, the critical barriers for each assembly and accompanying details will be included similar to those shown in Fig. i-9 and Fig. i-10. Placement and continuity of these critical barriers are also shown for each two-dimensional detail in the following chapters.
The next section introduces the two primary assembly design approaches that apply to the assemblies within this guide. Further discussion on each critical barrier and how each applies to the assembly design approaches is discussed in the following sections.
Assemblies within this guide provide the control functions as part of either a rainscreen design approach or mass wall design approach.
A rainscreen design approach is shown in Fig. i-9. This design approach assumes that moisture makes its way through the cladding plane while the building is in-service and provides a level of redundancy to protect against water ingress. A rainscreen assembly includes the following characteristics:
It is important to note that using rainscreen wall assemblies that exhibit good resistance to water penetration and that are fundamentally less sensitive to moisture ingress does not eliminate the need for implementing proper details and ensuring acceptable construction practices are followed. Improperly executed details are frequently sources of water entry, critically affecting the moisture performance of the assembly and contributing to premature weathering or efflorescence on the masonry veneer system.
A mass wall design approach is shown in Fig. i-10. It provides a WSS and WRB within the CMU structure. In recent years, the mass wall design approach has evolved to allow for thinner mass wall assemblies that control water through the use of clear surface-applied water-repellents and water-repellent admixtures.
In general, the water-shedding surface (WSS) is the outer surface of assemblies, interfaces, and details that will deflect and/or drain the vast majority of the exterior water from the assembly. In simplest terms, the WSS is the exterior surface of the building enclosure and the first line of defense against water ingress. The WSS reduces the rain load on the underlying elements of the assembly and serves as a solar control function to protect underlying components from ultraviolet (UV) exposure.
For the rainscreen design approach assemblies included within this guide, the WSS is the adhered or anchored masonry veneer. Because claddings can allow a significant amount of water behind the WSS, a means to drain this moisture out of the wall must be provided.
For the mass wall design approach assemblies included within this guide, the WSS is the single-wythe CMU wall structure, which contains surface-applied clear water repellent and water-repellent admixtures within the block and mortar.
For the additional details and transitions shown throughout this guide, the WSS also includes sheet-metal flashings, as well as the exterior face of fenestrations (e.g., windows), the roof membrane of a conventional roof assembly, and the top surface of the insulation of an inverted roof assembly, Example details included at the end of each assembly chapter demonstrate the location of the WSS at typical wall transitions and a window penetration.
The water-resistive barrier (WRB) is the second and last line of defense against water ingress. It is the surface within the wall assembly intended to prevent liquid water from traveling further into the assembly and is often relied upon for assemblies to remain watertight.
In rainscreen design approach assemblies that are exterior-insulated, the WRB may be the surface of the insulation if it is taped and sealed, or it may be a sheet- or fluid-applied sheathing membrane installed on the wall sheathing/structure as shown in Fig. i-11. To perform properly, it is critical that the WRB be continuous. For many standard wall assemblies, the WRB will be the sheathing membrane in combination with flashing and sealants at penetrations, i.e., the plane that sheds any incidental moisture out of the assembly to the exterior. Where the WRB is also part of the air-barrier system, it will be made airtight by tapes, sealants, gaskets, and other airtight components. WRB membranes for the rainscreen design approach assemblies within this guide may be designed as either vapor-permeable or vapor-impermeable:
A number of WRB products and systems are commercially available. However, two primary WRB products are shown within this guide for rainscreen design assemblies: sheet membranes (either mechanically attached or self-adhered) and fluid-applied membranes. Examples of these membrane types are shown in Fig. i-12 as well as Fig. i-13. Alternate types are also discussed where applicable in each assembly chapter.
A WRB system includes a WRB field membrane and accessory products such as flexible self-adhered flashing membranes, fluid-applied flashing membranes, sealants, tapes, and fasteners. These components, when combined, form the WRB system and may also perform as an AB system. When selecting a WRB system, the following properties should be considered:
In the mass wall design assemblies included within this guide, the WRB is the single-wythe CMU wall structure that contains surface-applied clear water repellent and water-repellent admixtures within the block and mortar.
Example details, two-dimensional details, and three-dimensional wall sections included at the end of each assembly chapter demonstrate the general installation of the WRB.
The air-barrier is a system of materials that controls flow of air through the building enclosure, either inward or outward. Air flow is significant with respect to heat flow (space conditioning), interstitial vapor condensation (water vapor transported by bulk air flow), and rain penetration control. AB systems should be impermeable to air flow, continuous across the building envelope, able to withstand the forces that act upon them (e.g., mechanical pressures, wind pressures, and stack effect), and durable over the life expectancy of the building enclosure.
For a rainscreen design approach, there are many types of AB products and systems available on the market today. A typical practice within the Northwest is to use a dual-function field membrane that has the performance properties of both an AB and a WRB. When this membrane is paired with accessory products (e.g., self-adhered flexible flashings, fluid-applied flashings, sealants, and/or tapes) and is detailed for airtightness, an AB system is provided.
Where the AB system is provided through the use of a mechanically attached sheet, it is attached to the structure with furring strips, masonry ties, cladding support clips, or washer head fasteners as recommended by the air barrier membrane manufacturer. Attachment provides long-term resistance to the pillowing effects of air pressure differentials. Where a self-adhered sheet membrane or fluid-applied membrane is used, the membrane bonds directly to the exterior sheathing or substrate for continuous support.
Other types of AB systems include:
For the mass wall design approach assemblies within this guide, the single-wythe CMU wall structure may provide the AB system.
Performance requirements for air barrier materials and air barrier systems specific to both rainscreen design approach and mass wall design approach assemblies are further discussed in the Thermal Performance and Energy Code Compliance section of this introductory chapter.
Example details included at the end of each assembly chapter demonstrate the location of a continuous air barrier at typical wall transitions and a window penetration.
Placement and continuity of thermal insulation is an important factor of a thermally efficient building enclosure. While not typically considered a critical barrier but more of a control function, the thermal insulation materials and line of insulation continuity (commonly referred to as the thermal envelope) are useful to identify. This barrier consists of insulation and other low-conductivity elements within an assembly or detail. Identification of these low-conductivity materials helps identify thermal bridges or any thermal discontinuities that should be addressed by design.
For a rainscreen design approach, the primary resistance to heat flow will be provided by thermal insulation (whether cavity or exterior insulation). Wood framing components will provide some insulating value, whereas steel stud framing will not.
For the mass wall design approach assemblies of this guide, the thermal insulation is either interior of the CMU structure or integral at CMU cores.
The Thermal Performance and Energy Code Compliance section of this chapter includes additional discussion related to the thermal envelope. It provides information on prescriptive thermal performance requirements of the energy code, how to address metal fasteners such as masonry veneer ties or cladding support clips that may penetrate exterior insulation, effective thermal performance of above-grade wall systems, special thermal performance discussion for concrete masonry unit (CMU) structures, insulation products, and air leakage as it’s required by energy code.
Example details included at the end of each assembly chapter demonstrate the location of the thermal envelope at typical wall transitions and a window penetration.
The vapor retarder/vapor diffusion 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. In the Northwest region, a vapor retarder is typically placed on the warm side of the insulation (high vapor pressure side).
A vapor retarder may not be necessary within some assembly designs in the Northwest region. Continuity of the vapor retarder is not necessary to adequately control vapor diffusion in most cases. Small holes, gaps, or tears are not critical, unlike in the air barrier. Section 1405.3 of the International Building Code (IBC) provides VR requirements for Northwest Climate Zones 5, 6, and Marine 4.
Vapor diffusion control is not to be confused with bulk air flow control (air barrier). Continuity and sealing of air barrier details is very important; if the same material is being used to control both vapor diffusion and air flow material continuity and air sealing is critical.
Common VR types used within above-grade wall structures in the Northwest region:
Building form and features including roof overhangs, balconies, canopies, and other protruding elements, etc., also play a critical barrier function whereby these elements deflect rain and provide shading from the sun and buffering from wind as shown similar in Fig. i-15. The protection provided by these components may allow for alternative water control strategies to be utilized at protected areas. For this reason, deflection elements can be considered as part of the critical barrier analysis. Conversely, balconies and other exterior architectural elements can also act as water-trapping features, unless carefully designed to prevent trapping water. The criticality of building form also depends on climate, and on rainfall in particular; therefore, building form and features are more critical in regions of greater rainfall (refer to Fig. i-7). Building form and features are not addressed within above-grade wall assemblies included within the remaining chapters of this guide but are important design components that should be considered on a project-specific basis.
The building thermal envelope is defined by the International Energy Conservation Code (IECC) as “the basement walls, exterior walls, floor, roof, and any other building elements that enclose conditioned space or provide a boundary between conditioned space and exempt or unconditioned spaces.” Note that the building envelope is sometimes referred to as the building enclosure.
The energy performance of buildings in the Northwest is governed by:
In general, these energy codes address the minimum requirements for both the thermal envelope and air barrier system critical barriers of the opaque above-grade wall assemblies included within this guide.
Within this guide, discussions related to the energy code focus on the above-listed codes and their commercial energy code compliance provisions; residential provisions are not explicitly addressed. Definitions of residential and commercial buildings may be found within the Definitions chapter of each of the codes listed above.
The energy codes that govern in the Northwest define the prescriptive thermal performance of above-grade walls that form the thermal envelope. Under commercial provisions, prescriptive performance requirements for opaque above-grade walls are differentiated in the IECC based codes by,
Table i-2 summarizes the prescriptive above-grade wall thermal envelope requirements as they apply to the assemblies of this guide. Requirements include both minimum R-value (located above each U-factor) and maximum U-factor. Minimum R-value requirements are for nominal insulation and include continuous insulation (ci), which is discussed in the Continuous Insulation section of this chapter. U-factors define the maximum thermal transmittance of the assembly when insulation and other bridging elements that are required to be considered by the governing code—such as framing members and, in some cases, cladding attachments and supports—are considered. For the purpose of this guide, the prescriptive U-factor has also been provided as an equivalent assembly effective R-value and is shown in parentheses ( ) below each U-factor in Table i-2. For simplicity, the R-value is the inverse of the U-factor.
Fig. i-17 describes the typical process for navigating energy code compliance options and strategies. It also describes how this process relates to assembly specific thermal performance results and discussion included within each assembly chapter.
Refer to Fig. i-17, which identifies the prescriptive compliance option for energy code compliance. Where a project seeks this compliance option, the above-grade wall assembly must meet one of the following:
An exception to the compliance strategies is denoted in the footnotes of Fig. i-17. Refer to the Chapter 4 discussion for more information regarding this exception.
Refer to Fig. i-17, which identifies the non-prescriptive compliance option (e.g., a trade-off strategy or whole-building modeling strategy). When a project seeks this compliance option, an above-grade wall assembly’s thermal performance is determined as a U-factor; however, it may or may not be required to meet the prescriptive values shown in Table i-2.
Discussion and numerous tables are available within Northwest energy codes and ASHRAE 90.1 to assist with determining the U-factors of above-grade wall assemblies. Where assemblies are not represented within these resources, various methods are available for calculating the effective thermal performance of the wall and are listed below. Appropriate calculation methods should be confirmed with the local jurisdiction as not all of these methods may be accepted:
Within this guide, three-dimensional computer modeling was employed for Chapters 1 through 3 and 5 through 8 assemblies to demonstrate how typical thermal bridges—like masonry ties, shelf angles, and cladding support systems of various types—contribute to the effective thermal performance of each assembly. Based on modeling results, insulation thicknesses and types as well as cladding support materials and types may be estimated for project-specific assemblies. Through evaluation of the results, numerous options for thermally optimizing each assembly are discussed. Modeling results and discussion are demonstrated in each chapter as an effective R-value but may be converted to a U-factor by dividing 1 by the R-value. Modeling does not account for the impact of thermal mass.
Thermal modeling was undertaken using HEAT3 (buildingphysics.com). Modeling specifics and additional information used to complete the modeling within this guide is provided in Appendix A.
Continuous insulation is referenced in the prescriptive requirements for many assemblies within this guide. Where continuous insulation is required or used to meet code compliance, the definitions of continuous insulation must be carefully considered; definitions vary by jurisdiction within the Northwest region and include:
Based on the above definitions:
The thermal performance of exterior insulation is reduced when penetrated by fasteners (metal or otherwise). Continuous insulation with no fasteners will perform near its nominal R-value. However, when fasteners—especially metal fasteners, which are highly conductive—penetrate the insulation, the nominal R-value is reduced. For this reason, metal fasteners (including masonry ties and cladding support clips) may need to be considered for energy code compliance.
The definition of a fastener or metal fastener may vary by code and jurisdiction. Continuous insulation is also not directly defined by the IECC. As a result, the local governing jurisdiction should be contacted for determining when fasteners are to be considered. Below, some general clarifications are provided for assistance.
A mass wall has the ability to store thermal energy (i.e., heat) that can be released at a later time, reducing peak heating and cooling loads and increasing occupant thermal comfort. The benefit of thermal mass varies with climate zone and is more beneficial in warmer climates; however, thermal mass can still provide some benefit in cooler climates. Energy codes within the Northwest region take into consideration thermal mass properties by allowing mass wall assemblies to meet lesser prescriptive R-values (greater U-factors) than framed wall types. When complying with the energy code through a whole-building modeling approach, the benefits of thermal mass are directly considered within the building model.
The 2012 IECC, WSEC, and SEC and the 2014 OEESC define a mass wall as “weighing not less than 35 psf of wall area; or not less than 25 psf of wall area if the material weight is not more than 120 pcf.” Under this definition, 6-inch or larger lightweight (103 pcf) CMU or heavier block qualifies as a mass wall, as does a typical concrete backup wall. The classification of a “mass wall” typically encompasses the backup wall structure; veneer inclusions should be confirmed with the local governing jurisdiction. Chapters 1, 4, 5, and 6 assemblies with CMU backup wall structure typically qualify as mass walls.
In the states of Oregon and Washington (excluding the City of Seattle), integrally insulated CMU walls such as the Chapter 4 assembly are exempt from prescriptive performance R-value and U-factors when the following two conditions are met:
A variety of insulation products exist on the market today for wall cavities, integral insulation, and continuous (interior or exterior) insulation.
For wall cavities, unfaced fiberglass or mineral fiber batts are most common. High-density versions of either batt can be found and assist with achieving a greater assembly effective R-value without increasing wall depth, especially in wood-framed wall assemblies. Due to the significant reduction in effective thermal performance for steel-framed wall assemblies (typically 40 to 60%), a high-density batt provides little benefit over lower-density batt products. Batt insulation widths and thicknesses range in size to accommodate most standard wood and steel framing depths. Wall cavity insulation may also include sprayed polyurethane foam insulation, which is available in both open- and closed-cell varieties and varies in thermal resistance and vapor permeance.
Where split insulation occurs (e.g., both wall cavity and exterior insulation) it is important to consider the air- and vapor-permeability of the both the selected insulating materials and WRB field membrane. These considerations are discussed in each assembly chapter.
Where continuous insulation is required, several types of board insulation products are available.
Integral insulation, which may be used within the assemblies of this guide, may be loose-fill such as perlite but is commonly provided by a expanding foam-in-place insulation product. Foam-in-place insulation is typically injected through ports drilled within the CMU mortar joints. An example of foam-in-place insulation is shown in Fig. i-20.
Energy codes within the Northwest have mandatory air leakage requirements. Requirements include a continuous air barrier throughout the building thermal envelope (i.e., surrounding conditioned and semi-heated spaces). The air barrier must be continuously sealed and supported by the structure (e.g., with fasteners or adhered to the sheathing). Air barrier compliance options for each Northwest code are provided below. All members of the design and construction team should be familiar with the air barrier requirements specific to their jurisdiction.
The following checklist items can increase the success rate for the design and installation of a continuous air barrier in all jurisdictions.
Within the IECC-based codes, opaque thermal envelope assembly requirements are grouped into “Zone 5 and Marine 4” and “Zone 6”. Although IECC-designated climate Zones 5, 6, and Marine 4 all occur within the state of Washington, the Washington State Building Code Council has determined that all zones must meet the “Zone 5 and Marine 4” requirements. This determination is reflected in Table i-2.
Project-specific thermal performance values for opaque above-grade wall assemblies 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.
When looking at actual heat loss calculations (e.g., mechanical equipment sizing or energy modeling) the assembly effective R-value with all fasteners should be considered.
The term “thermal bridging” is not defined by the energy codes that govern the Northwest region (Washington, Oregon, and Idaho). However, the 2013 ASHRAE Handbook of Fundamentals recognizes thermal bridging as “passing highly conductive materials through insulation layers.”
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.
For above-grade wall assemblies in the Northwest, vapor-impermeable exterior insulation and vapor-impermeable air and water-resistive barrier membranes may be used when the assembly insulation is located exterior of the air and water-resistive barrier or when the exterior insulation is 1/2 to 2/3 of the total nominal insulation R-value in the assembly. This reduces the risk of condensation development within the wall cavity. Vapor-impermeable products and greater insulation R-value splits may be considered but should be carefully evaluated based on project-specific characteristics.
Sheet-metal components deflect liquid water and are used In both rainscreen and mass wall design approaches and typically occur above and below wall penetrations, as parapet caps, and as counterflashing elements to protect flashing membranes. In a rainscreen design approach, cross-cavity sheet-metal flashings deflect water within the rainscreen cavity back to the exterior environment while still allowing cavity ventilation.
The location of sheet metal flashings should be carefully planned for each project but, at minimum, should be located:
Sheet-metal flashing profiles should include a projected hemmed drip edge and positive slope. For cross cavity sheet metal flashings, a minimum 4-inch-tall back leg should be provided and should be shingle lapped into the WRB system. Where serving as a counterflashing, the sheet metal should counterflash cladding a minimum of 1.5 inches (where possible) and project a minimum of half an inch beyond the cladding face to avoid blocking ventilation. The vertical location of the sheet-metal flashing in relation to the masonry veneer must be considered. Adequate spacing between the sheet metal and veneer above and below will ensure building movement does not affect the sheet-metal flashing profile or its function.
In a rainscreen design approach, folded end dams assist with deflecting water away from the rainscreen cavity and should be provided at all flashing terminations (e.g., at the ends of a window head flashing).
Where sheet-metal laps occur, laps should either be fully sealed with a high-quality silicone or butyl-based sealant or may be soldered. Laps within sheet-metal parapet coping should be standing-seam.
It is a best practice to construct masonry veneer sheet-metal flashings from stainless steel. Stainless steel is relatively inert to the corrosiveness of mortar and provides a similar level of durability and longevity as the masonry veneer. Prefinished galvanized sheet-metal products may be used in masonry veneer applications; however, they may require replacement before the masonry veneer does.
Where exterior insulation is used, cross-cavity sheet-metal flashings create a thermal bridge. An alternate to a sheet-metal flashing at anchored veneer assemblies is to provide a flexible self-adhered flashing membrane that is fully supported by the insulation and lapped into the WRB as shown in Fig. i-27. This flexible membrane is shingle-lapped over the bearing element (typically a standoff shelf angle) and onto a sheet-metal drip flashing.
A cross-cavity flashing and through-wall flashing are commonly used interchangeably; however, there is a technical difference. A cross-cavity flashing is integrated with the WRB and extends through the rainscreen cavity. A through-wall flashing extends through the entire depth of the wall, such as one might find at the base of a CMU wall.
Over time, volumetric changes will occur within any above-grade wall assembly and can be the result of changes in temperature, moisture, elastic deformation, settlement, and creep. The amount of movement that occurs will depend on the building materials used within the wall assembly as well as on the intensity of the influencing mechanism (e.g., temperature change). In general, wood frame members, concrete, CMU, and stone will shrink, whereas clay masonry will expand. If steel studs or a CMU backup wall are used and are properly protected, minimal volume change is expected.
Different materials within each above-grade wall assembly may also move differently in relation to one another as shown by the example in Fig. i-29. If not properly designed for, differential movement can cause unwanted cracking, spalling, buckling, settlement, or separation within the building structure or veneer.
For the purpose of this guide, discussion and design of movement joints are considered as they relate to differential movement between the veneer and wall structure and also include control and expansion joints. The consideration for locating and sizing building expansion joints that occur within the wall structure is beyond the scope of this guide but must be appropriately designed for and integrated into the above-grade wall system where they occur.
The discussion of building movement in this guide is meant to be a general reference; it is the responsibility of the Designer of Record to appropriately design for building movement.
This section identifies general rules for locating movement, expansion, and control joints as they relate to the 8 primary wall assemblies in this guide.
There is no single set of recommendations for the placement and design of movement joints that will work for all projects. Additionally, joints may be added more frequently than is necessary for aesthetic purposes. In general, the following locations for movement joints within a masonry veneer or structure should be considered in addition to the above.
Note that placement of horizontal joints are also recommended at various locations for a rainscreen design approach to allow for cavity drainage and ventilation. These locations are further discussed and identified within each chapter and with an asterisk (*) in chapter details.
Joints that accommodate vertical movement should either include a sheet metal flashing or a backer rod and sealant joint. Joints that accommodate horizontal movement should receive a backer rod and sealant joint. Movement joints should be designed and constructed to accommodate 3 to 4 times the amount of anticipated movement and should be no narrower than 3/8 of an inch. Movement joints should be free of debris, reinforcing, or other elements that may inhibit movement over the life of the building.
Joint sealants are a critical component of a movement joint and allow the joint to open and close uninhibited while providing a continuous water-shedding surface. Sealant products ideal for use at masonry movement joints have the following properties:
The following joint design best practices will ensure long-term performance of a movement joint:
Where there is a desire to minimize the visual appearance of masonry veneer movement joints, the following may be considered:
In the Northwest region, surface-applied clear water repellents are commonly applied to the surface of masonry veneer claddings and exposed CMU walls for the assemblies featured within this guide. Elastomeric coatings may also be used in targeted applications. The success of a clear water repellent or elastomeric coating is reliant on appropriate product selection, cleaning procedures, and application methods. Although the use of these products provides a number of purposes, as described below, these products do not make up for poor masonry workmanship or detailing. This guide section covers cleaning and best practices for selection and application of clear water sealers and elastomeric coatings.
Debris and contaminants, including oil, grease, dirt, ash, and hydrocarbons, need to be cleaned from new masonry products prior to clear water repellent or elastomeric coating application. A number of cleaning methods are available, including hand, water, or chemical cleaning and abrasion.
Select cleaning procedures based on masonry and mortar colors, texture, and the type of existing debris or contaminants. In general, select the least aggressive cleaning method necessary to remove debris and contaminates. Over-cleaning masonry products or using excessive abrasion can alter the appearance of the masonry veneer or CMU and can encourage premature weathering.
For all cleaning methods, test-clean an inconspicuous area of the wall to confirm the effectiveness and acceptability of the cleaning method. Water clean only when temperatures exceed 40˚F; even warmer temperatures may be required for applications of chemical cleaning products that rely on a chemical reaction to be effective.
ASTM D5703 and BIA Technical Note 20 are helpful resources for determining appropriate cleaning procedures for clay masonry units, whereas NCMA TEK 8-4A provides helpful discussion on cleaning CMU block of various types and finishes. Also consult the masonry unit or CMU manufacturer and cleaning product manufacturer (where applicable) prior to cleaning.
A surface-applied clear water repellent is recommended for the assemblies in this guide that include adhered or anchored unglazed clay masonry veneer or exterior-exposed CMU. Application of a clear water repellent can reduce water absorption of masonry veneer and CMU, as demonstrated in Fig. i-36, while preserving or enhancing natural appearance. By reducing how much water the masonry cladding absorbs, less frequent wetting/drying and freezing/thawing cycles are expected to occur, reducing the likelihood of premature weathering and water-related damage and staining.
There are two primary types of repellents: penetrating or film-forming.
Of the two repellent types, penetrating repellents are recommended for use within the Northwest.
For unglazed clay masonry and CMU in the Northwest, use a silane/siloxane blend clear water repellent.
Both silanes and siloxanes chemically bond to clay masonry, CMU, and mortar in the presence of moisture and alkalinity; as a result, silane/siloxane-based repellents can provide 5 to 10 years of protection, making such blends a durable and relatively longer-lasting water repellent option.
A penetrating silicone-based repellent may also be considered and may provide greater anti-graffiti properties than a silane/siloxane blend. Silicone-based repellents have less chemical bonding ability to clay masonry, mortar, and CMU than silane/siloxane blends have; thus, silicone-based repellents need to be reapplied more frequently than silane/siloxane-based products.
Clear water repellent application to glazed masonry veneers is not recommended. Glazed surfaces reduce the penetrating ability of clear water repellent products, limiting the effectiveness of the application.
When selecting a clear water repellent, the following characteristics/properties are desirable for long-term performance:
Where anti-graffiti repellent properties are desired, use a vapor-permeable silicone-based repellent with penetrating properties. The anti-graffiti repellent should provide similar vapor permeance and water penetration resistance to that listed above. The effectiveness of anti-graffiti properties is demonstrated through ASTM D7089 results, which may be used to compare the ease of graffiti removal.
Clear water repellents should not be used as a replacement for a water-resistive barrier or air barrier within a masonry assembly. Water repellents are also not effective at bridging cracks or filling voids that result from poor joint design/installation or from long-term building movement. Although clear water repellents will increase the masonry’s ability to shed water, a repellent will not prevent efflorescence as a result of water intrusion behind a masonry veneer and will require reapplication to be effective over the long-term service life of the building.
The following general procedures and considerations are the best practices for clear water repellent application:
Elastomeric coatings reduce the amount of water absorbed by masonry substrates and also provide crack-bridging properties that help reduce water leaks. Elastomeric coatings are typically installed where additional water penetration resistance is desired and where a painted surface is visually acceptable. An example of an elastomeric-coated CMU wall is shown in Fig. i-38. Elastomeric coatings can serve as a water-shedding surface, water-resistive barrier, and air barrier on the exterior face of a masonry substrate when a UV-stable coating is used.
A vapor-permeable silicone or acrylic elastomeric coating with UV resistance and high elongation properties is recommended for a good coating. A vapor-permeable coating will allow the masonry substrate to dry and reduces the likelihood of salt buildup and bubbling or blistering of the coating.
When selecting an elastomeric coating, the following characteristics/properties are desirable for long-term performance:
Elastomeric coatings can exhibit staining and may be difficult to clean. Surface staining is largely attributed to surface wetting below horizontal surfaces and penetrations including flashings, windows, and parapets. Therefore, staining can largely be reduced by reducing the amount of water that runs off onto the wall from these dirt-collecting surfaces. The use of sheet-metal drip edges (such as at window and door sills) is recommended to deflect water away from the surface of the masonry coating to help reduce staining.
The following general application procedures and considerations are the best practices for elastomeric coating application:
The remaining chapters within this guide address assembly-specific considerations for the 8 primary above grade wall assemblies.