Chapter 8: Thermal Performance & Energy Code Compliance

Table of Contents

Chapter 1: Introduction

Chapter 2: Masonry Systems

Chapter 3: The Building Enclosure

Chapter 5: Quality Control & Assurance

Chapter 7: Single-Wythe CMU Systems

Chapter 8: Thermal Performance & Energy Code Compliance

Appendix A:

Thermal Modeling

Glossary of Terms

Terms

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Air and thermal control layers manage heat flow across the building enclosure, influencing the amount of energy and fuel required to heat and cool a building and affecting occupant thermal comfort and condensation risk. Chapter 3 discusses the basic function of the air and thermal control layers.

In Colorado and southern Wyoming, air control layer performance requirements and the thermal performance of opaque above-grade wall assemblies (e.g., masonry wall systems) is governed by locally adopted energy codes. Thus, this chapter discusses basic the air and thermal control layer in the context of energy code compliance requirements for whole-building air leakage and thermal performance, specifically conductive heat flow, of masonry wall systems. At the end of this chapter are design tables, which may be used to estimate the thermal performance of typical masonry systems and their components.

Governing Energy Codes

In Colorado and southern Wyoming, building codes are adopted and enforced at the local level. While there is no statewide energy code, legislation passed in Colorado in 2007¹ set the 2003 International Energy Conservation Code (IECC)² as the minimum-required energy code for all jurisdictions in the state that have adopted building codes. In jurisdictions where no building codes have been adopted, the state requires that hotels, motels, and multifamily buildings³ conform to the 2015 IECC.⁴ In addition, factory-built structures⁵ are required to conform to the minimum requirements of the 2009 IECC⁶ where the locally adopted code is less stringent than the 2012 IECC.⁷ Public buildings are required to conform to the 2015 IECC⁴ statewide.

Most larger jurisdictions within Colorado have adopted the 2009,⁶ 2012,⁷ or 2015 IECC,⁴ and several of these jurisdictions have enacted local amendments to the governing version of the IECC. This guide addresses some of these amendments; however, the Designer of Record is responsible to refer to code amendments of the authority having jurisdiction on a project-specific basis. Additionally, this guide references general 2018 IECC requirements, which have not yet been enacted by any jurisdiction at the time of publication.

Table 8-1 summarizes the governing energy codes for various jurisdictions within Colorado and southern Wyoming at the time of publication. Refer to the Colorado Department of Local Affairs website for the current IECC adoptions by county.⁹ In general, these energy codes address the minimum requirements for both the air and thermal control layers of the opaque above-grade wall systems.

Air Control

It is a building enclosure best practice and energy code requirement to provide an air control layer. The previous chapters in this guide discuss the air control layer (see Control Layer Summary on page 21) and specific air barrier systems (see Table 6-2) commonly used with masonry wall systems. As demonstrated in Fig. 3-8 on page 19, the air control layer has relationships with all of the building enclosure loads listed, including heat flow, making it a critical component of the building enclosure. Unintentional air flow across the enclosure can be defined as air leakage and is specifically addressed by the governing energy codes in the state of Colorado and southern Wyoming. Maximum air leakage targets are typically prescribed in local energy codes as maximum allowable flow rates at a specified pressure differential across the building enclosure.

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Code Air Leakage Requirements

The governing energy codes within the state of Colorado and southern Wyoming require a continuous air barrier system throughout the building’s thermal envelope that is continuously sealed and supported by the structure (e.g., fastened or adhered). The 2015 IECC defines the building thermal envelope 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.” ⁴ Note that the thermal envelope may not always occur at the building enclosure.

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Prescriptive air leakage requirements vary by the governing version of the IECC as well as local code amendments. IECC air leakage requirements for above-grade wall assemblies are summarized in Table 8-2. This table is not inclusive of all IECC air leakage provisions or local amendments. This guide recommends that all members of the design and construction team be familiar with the specific air leakage requirements of the governing jurisdiction as well as project-specific performance targets.

Both the 2012 and 2015 IECC provide a whole-building air leakage testing compliance option as an alternative to certain prescriptive requirements for the air permeance of materials and/or air leakage of assemblies as well as specific installation requirements. If pursuing this compliance option, the rate of air leakage for the whole-building may not exceed 0.40 cfm/ft² under a pressure differential of 0.3- inch water gauge when tested in compliance with ASTM E 779²⁰ or an equivalent method approved by the code official. Whole-building air leakage testing is typically completed by pressurizing and depressurizing the building with multiple blower door setups as shown in Fig. 8-2.

The cities of Fort Collins and Boulder have both introduced amendments to the IECC that include provisions for mandatory whole-building air leakage testing. These requirements are summarized below:

City of Fort Collins (2015 IECC with amendments): ¹¹ The maximum-allowable whole-building air leakage rate is 0.25 cfm/ft² at 0.3 in-H₂O (75 Pa) when tested in accordance with the City of Fort Collins Building Air Leakage Test Protocol for commercial buildings²¹ or the City of Fort Collins Building Code Protocol for New Multifamily Building Airtightness Testing. ²² Failure to comply with the maximum-allowable leakage rate requires a diagnostic evaluation in accordance with ASTM E1186-03 (2009),²³ followed by repair and retesting of the air barrier system.
City of Boulder (2017 COBECC, based on the 2012 IECC): ¹³ The maximum-allowable whole-building air leakage rate is 0.40 cfm/ft² at a pressure differential of 0.3 in-H₂O (75 Pa) when tested in accordance with ASTM E779. ²⁰ In addition, a sampling of dwelling units must be tested using a blower door in multi-unit residential buildings to demonstrate that the maximum air leakage rate in any one dwelling does not exceed 0.25 cfm/ft² at a pressure differential of 0.2 in-H₂O (50 Pa). The sampling must include at least 20% of the units in each building, at least one of each unit type, and approximately an equal number of units on each floor level. Any unit that fails the above-noted testing requirement must be diagnosed, the air barrier system corrected, and the unit retested. A minimum of two additional dwelling units must be tested for each failed test.

Checklists for Successful Air Barrier Design and Construction

Regardless of the governing air leakage requirements and path to compliance, the air barrier is an essential control layer. The construction and design checklist items provided on page 125 can be used to increase the likelihood of a successful design and installation for a continuous air barrier system in any jurisdictions. These checklists were adapted from the National Masonry Systems Guide: Northwest Edition. ²⁴

Design Checklist

Select appropriate air barrier system materials and assemblies. Refer to Table 8-2 for air barrier system materials and assembly properties. The Air Barrier Association of American (ABAA) also lists several commercially available compliant air barrier membrane products and systems at www.airbarrier.org. ²⁹
Ensure that a continuous line representing the plane of airtightness can be drawn across all wall assemblies, details, and transitions between assemblies. This includes in both plan and section perspectives. Details included within this guide demonstrate this practice; an example is shown in Fig. 8-3.
Clearly delineate the air barrier system boundary on the construction documents. This practice is typically performed on the floor plans for each building level and on each building section as shown in Fig. 8-4. This delineation is required by the City of Fort Collins energy code (local amendments to the 2015 IECC) for compliance,¹¹ in addition to the calculation of the air barrier pressure boundary surface area.
Identify air barrier system installation, testing, and installer qualification requirements in Divisions 1 and 7 of the project manual. Air barrier master specifications related to Divisions 1 and 7 are available from the ABAA’s website and may be modified to meet local code and project-specific requirements.

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Construction/Installation Checklist

Prior to the installation of air barrier system components, coordinate an air barrier system preconstruction meeting with the general contractor, designer(s), and the trade/ subcontractor responsible for the installation of the air barrier system as well as all additional trades whose work may interface or penetrate the air barrier system (e.g., window installers, framers, siders, mechanical, etc.). Clarify the responsibilities of all parties involved with the air barrier system installation and review installation requirements and limitations of the system as well as any details/installations that will require significant coordination efforts to implement.
Use installers who are experienced with the specific air barrier system installation to perform the installation of air barrier components. For example, if the primary air barrier strategy is a sealed sheathing approach, using an installer with experience installing sealed sheathing can increase the likelihood for quality air barrier installation.
Designate an air barrier system/building enclosure supervisor or superintendent from the construction team to oversee all trades involved in installation related to the air barrier system.

Build freestanding mock-ups of all project-specific typical and unique air barrier system details. Retain building mock-ups for training and reference purposes throughout construction.
Perform qualitative diagnostic air leakage testing of mock-up installations to identify deficiencies. Correct deficiencies and retest to demonstrate that deficiencies have been resolved. Refer to ASTM E1186²³ for air leakage site detection practices.
Implement a quality control program. Develop a checklist of items that need to be reviewed before the air barrier system is covered with additional elements such as exterior insulation and cladding.
Provide third-party quality assurance reviews of installed air barrier detailing and provide periodic diagnostic air leakage testing to ensure airtight transitions, especially at roofto-wall and wall-to-foundation transitions and at the floor line and window perimeter details.
Execute whole-building air leakage testing prior to covering, when possible. This limits the need to remove building elements (such as cladding) to correct deficiencies.

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Thermal Control

In a masonry wall system, the thermal control layer of the field of wall area is provided by one or more layers of thermal insulation. All insulation products share the same underlying physical property: the material has a relatively low conductivity such that it resists heat flow better than other system components. Regardless of the cladding type, the thermal control layer will almost always be interrupted by materials with greater conductivities due to the need to transfer structural loads. For example, insulation located within a framed wall cavity is commonly interrupted by framing members as shown in Fig. 8-5, and exterior insulation is often interrupted by masonry anchors as shown in Fig. 8-6. When insulation is interrupted by elements of a higher conductivity, more heat flow occurs through the more highly conductive materials as the path of least resistance, degrading the overall thermal performance of the insulation layer. This phenomenon is commonly known as thermal bridging. The conductive thermal performance of a masonry system is thus determined by the insulation’s ability to resist heat flow, the quality of its installation, and the degree to which the insulation is interrupted or bridged.

Minimizing thermal bridges within the building enclosure is a best practice and is often an energy code requirement. The basic principles of thermal control are discussed in the Control Layer Summary on page 21. The following section addresses specific insulation types and thermal control considerations.

Insulation Types

A variety of insulation products exist for use in exterior walls; common insulation products used within masonry wall systems are described on the following page. Additional insulation products are available but are not as common for masonry wall systems in Colorado and southern Wyoming. Where split insulation occurs within the wall assembly (e.g., both wall cavity and exterior insulation), it is important to consider both the air- and vapor-permeance of the insulating material and the air barrier and WRB system.

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Exterior Insulation Considerations with Masonry Veneers

Exterior insulation outboard of the backup wall structure and behind the veneer is a common insulation strategy for improving the thermal performance of an anchored masonry veneer wall system. The type of exterior insulation is dependent on several factors and is further discussed in Chapter 5.

As mentioned in Chapter 5, building codes and standards provide prescriptive attachment requirements for cladding. Where the masonry veneer weighs less than 40psf and where the ASCE-7 wind velocity pressure is less than 55psf, a maximum air cavity depth of 6 5⁄8 inches is allowed behind the masonry veneer. If the veneer weight and project-specific wind loads do not exceed these values, prescriptive attachment requirements can accommodate up to 4 5⁄8 inches of exterior insulation within the cavity, allowing for the recommended 2-inch air gap behind masonry veneer.

The exterior insulation behind an anchored masonry veneer will be bridged to some degree by the anchorage system. Thermal bridging from the anchorage system degrades the insulation’s thermal performance. Whether the exterior insulation can be considered continuous for code-compliance purposes is dependent on the specific anchoring system used and code interpretations by the authority having jurisdiction and is discussed in the Continuous Insulation section of this chapter. This guide recommends clarifying with the authority having jurisdiction on a project-specific basis whether exterior insulation is considered continuous for code-compliance purposes.

Masonry Anchors

Masonry anchors, such as those shown in Fig. 8-7, act as thermal bridges when installed through exterior insulation; however, the degree to which the anchoring system degrades the thermal performance of the exterior insulation depends on several factors, primarily the following:

Masonry Anchor Geometry: The greater the penetration area of the anchor that bridges the insulation, the greater the conductive heat loss through each anchor. An example of the thermal bridging created by a galvanized-steel masonry anchor is shown in Fig. 8-8.
Anchor Material: The greater the conductivity of the anchor materials, the greater the conductive heat loss and the more severe the thermal bridging. For example, stainless-steel anchors are more thermally efficient than mild-steel anchors because the conductivity of stainless steel is approximately 1 ⁄3 that of the mild steel. In addition, some proprietary anchors have been thermally optimized and incorporate low-conductivity components to minimize thermal bridging.
Anchor Spacing: The greater the spacing between anchors, the more thermally efficient the anchorage system; however, spacing needs to be coordinated with structural requirements.

From the thermal modeling results presented in the Masonry System Thermal Performance Design Tables, the masonry anchor systems considered can be ordered from most thermally efficient to least thermally efficient as follows for typical anchor spacing:

Stainless-steel embedded wire anchor (only applicable for CMU backup wall structures)
Stainless-steel plate anchor
Thermally optimized screw anchor with galvanized- or stainless-steel hook
Galvanized-steel embedded wire anchor (only applicable for CMU backup wall structures)
Galvanized-steel plate anchor

Masonry Shelf Angle Supports

Intermediate bearing support of anchored veneer systems is commonly provided by lintels or shelf angle supports at floor lines or above fenestration rough openings. These supporting elements bridge exterior insulation that may exist within the masonry veneer air cavity.

Shelf angles attached tight to the structure (e.g., a continuous shelf angle), as shown similarly in Fig. 8-9a, continuously bridge exterior insulation, resulting in a significant thermal bridging effect. To reduce the insulation area bridged by the shelf angle and improve thermal performance, the shelf angle can be off-set from the structure to the depth of the exterior insulation (e.g., a standoff shelf angle) using intermittent supports as shown similar in Fig. 8-9b. The intermittent supports may use hollow steel sections (HSS), knife plates, or proprietary standoff anchor systems.

Standoff shelf angle supports with exterior insulation, such as that shown in Fig. 8-10, are increasing in popularity. Due to the lesser degree of thermal bridging, a thinner exterior insulation thicknesses can be used to meet similar thermal performance requirements than if a continuous shelf angle support was used. For example, as determined from the thermal modeling results discussed later in this chapter, a continuous shelf angle support may require up to an additional half-inch of insulation to provide a comparable effective thermal performance value as standoff shelf angle support for wood stud–framed systems. For steel-stud and concrete masonry unit (CMU) backup wall structures, an additional 2 inches of exterior insulation or more may be needed to off-set the thermal losses created with using a continuous shelf angle as opposed to a stand-off shelf angle. The thermal bridging at both continuous and standoff shelf angles can be visualized from the three-dimensional thermal modeling images shown in Fig. 8-11.

Mass Wall Considerations

A mass wall can store thermal energy (i.e., heat) that can be released later, reducing peak heating and cooling loads and improving occupant thermal comfort. The benefit of thermal mass varies with climate zone and is generally more beneficial in warmer climates, particularly in areas with large daily temperature swings; however, thermal mass can still provide some benefit in cooler climates, especially in spaces with high passive solar heating. The IECC has less-stringent prescriptive thermal performance requirements for mass walls when compared to framed wall types. When complying with the energy code through a whole-building modeling approach, any dynamic heat transfer and storage effects of thermal mass are directly considered within the building model.

The 2009,⁶ 2012,⁷ 2015,⁴ and 20188 versions of the IECC in general define a mass wall as weighing more than 35 psf of wall surface area or weighing more than 25 psf of wall surface area when the material weighs less than 120 pcf.^{4, 6, 7, 8} Furthermore, the 2015 and 2018 IECC clarify that mass walls may also include walls having a heat capacity that exceeds 7 Btu/ft² degree F or walls having a heat capacity greater than 5 Btu/ft² degree F when the material weight is not more than 120 pcf.^{4, 8}

The mass wall classification is typically determined by the backup wall structure and does not consider the mass from masonry veneers; however, this guide recommends confirming the treatment of veneer mass with the authority having jurisdiction. Masonry wall systems that include a CMU wall structure typically qualify as mass walls.

Integrally Insulated Mass Walls

In partially grouted CMU structures, the ungrouted cores can be insulated to form an integrally insulated mass wall. Integral insulation may be loose fill, such as perlite, but it is more commonly a resinous, foam-in-place insulation product that is post-applied through ports in the CMU mortar.

With conventional integrally insulated CMU walls, thermal bridging will occur through CMU webs and grouted cores, and it is typically not possible to comply with prescriptive thermal performance targets using the core insulation alone. Improved thermal performance can be achieved using proprietary composite CMU block products. These products typically incorporate rigid foam board inserts and optimize CMU web and core design to minimize thermal bridging and are discussed in Chapter 7. These products may be able to meet prescriptive energy code compliance mass wall code requirements without the need for additional interior or exterior insulation. For effective R-value capabilities of proprietary insulated CMU products, consult the manufacturer.

Thermal Control: Energy Conservation Code Requirements

This guide addresses energy code compliance specific to opaque above-grade wall systems under the 2009, 2012, 2015, and 2018 IECC code commercial provisions; residential provisions are not addressed. Definitions of residential and commercial buildings may be found within the Definitions chapters of each code. Under commercial provisions, the prescriptive performance requirements for opaque above-grade wall systems are differentiated by:

Climate zone, as shown in Fig. 8-12: Zone 4B, Zone 5B, Zone 6B, or Zone 7B
Occupancy: All Other or Group R, if operating under the 2012 IECC or later
Wall classification: mass, metal-framed (i.e. steel studframed), wood-framed (i.e. wood stud–framed), or other

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Fig. 8-13 describes the typical process for navigating the opaque above-grade wall system thermal enclosure energy code compliance options and strategies. It also describes how this process relates to the system-specific thermal performance results and discussions provided in the design tables through this chapter. Refer to Table 8-3 on page 128 for a summary of common insulation products.

Prescriptive Energy Code Compliance

Refer to Fig. 8-13 for the prescriptive compliance options for energy code compliance. Where a project seeks this compliance option, the above-grade wall system must demonstrate compliance with one of the following strategies:

Insulation R-Value Method: The assembly thermal insulation R-value must meet or exceed the minimum nominal insulation R-value(s) listed in Table 8-4. For example, under the 2015 IECC,4 a Group R project in Climate Zone 5B with a wood-framed backup wall requires at least a nominal R-13 wall cavity insulation with R-7.5 continuous insulation or, alternatively, R-20 cavity insulation with R-3.8 continuous insulation to meet this compliance strategy.15 Where continuous insulation is denoted, defer to the interpretation of the governing jurisdiction; where continuous insulation (ci) is denoted, defer to the interpretation of the authority having jurisdiction.
Assembly U-Factor Method: The assembly U-factor must be less than or equal to that listed in Table 8-4. For this strategy, the project-specific assembly U-factor will need to be determined either through calculations or table values. A U-factor defines the maximum thermal transmittance of the system when insulation and other bridging elements are considered (e.g., framing members and, in some cases, cladding attachments and supports). For the purpose of this guide and for ease of reference, the prescriptive U-factor in Table 8-4 is also provided as an equivalent effective R-value, shown in parentheses. For simplicity, the R-value is the inverse of the U-factor.
Component Performance Alternative: The assembly U-factor may exceed that listed in Table 8-4; however, the summation of the area-weighted U-factors for all assemblies at the thermal enclosure may not exceed that required by the code, as described by Equation 8-1:

Nonprescriptive Energy Compliance

Fig. 8-13 identifies the nonprescriptive compliance option (e.g., whole-building modeling strategies). When a project seeks this compliance option, the thermal performance of an above-grade wall assembly is determined as a U-factor; however, it may or may not be required to meet the prescriptive values shown in Table 8-4. This option allows the designer to trade-off the performance of the thermal enclosure with mechanical (i.e., HVAC) and lighting systems.

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Continuous Insulation

Energy code requirements reference continuous insulation; however, the definition of continuous insulation and its interpretation needs to be carefully considered as it can vary by code and the authority having jurisdiction:

2009 and 2012 IECC: No definition provided. This guide recommends confirming local requirements with the authority having jurisdiction. ^{6, 7}
2015 and 2018 IECC: “Insulating material that is continuous across all structural members without thermal bridges other than fasteners and service openings. It is installed on the interior or exterior or is integral to any opaque surface of the building envelope.” ⁴

In general, continuous insulation is typically interpreted as follows:

Continuous insulation can be interior, exterior, or integral to the building envelope.

Insulation bridged by continuous structural members (such as steel studs in a framed wall) is not considered continuous. Insulation bridged by external structural members, whether continuous or intermittent (such as cladding attachment systems and masonry shelf angle supports) may or may not be considered continuous.
Fasteners have no impact on whether insulation is classified as continuous. However, when fasteners— especially metal fasteners, which are highly conductive— penetrate the insulation, the effective R-value is reduced. Various versions of the IECC do not provide a definition for a fastener; whether cladding attachment systems such as masonry veneer anchors are considered fasteners depends on the definition interpretation.
Service openings (e.g., doors, ducts, etc.) have no impact on whether insulation is classified as continuous or not.

This guide recommends clarifying continuous insulation requirements with the authority having jurisdiction on a project-specific basis.

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Determining Wall Assembly U-Factors

The most convenient method for determining the thermal performance or U-factor for a wall assembly is to use an industry-accepted default value. Appendix A of ASHRAE 90.1³¹ is a commonly used and industry-accepted resource to obtain tabulated U-factors for various wall assembly and insulation configurations. Where accepted, tabulated values are not always representative of the proposed wall assembly. Various methods are available for calculating the thermal performance of the wall and are listed below. Confirm appropriate calculation methods with the local jurisdiction, because not all methods may be accepted:

Parallel Path and Isothermal Planes (refer to the ASHRAE Handbook of Fundamentals):³² The parallel path method is typically used for wall assemblies with relatively nonconductive thermal bridges such as wood studs or plastic materials. The isothermal planes method is more appropriate when the thermal bridge material is moderately conductive, such as with the concrete web between insulated CMU cores in an integrally insulated CMU wall. These methods are not reliable for assemblies with highly conductive materials (e.g., steel studs) or intermittent components such as fasteners or anchors through exterior insulation
Zone Method and Modified Zone Method (refer to the ASHRAE Handbook of Fundamentals):³² Typically used for assemblies with highly conductive elements that bridge the insulation, such as steel studs. These methods are not recommended for determining the performance of assemblies with intermittent fasteners or anchors through exterior insulation.
Two-Dimensional Computer Modeling: Programs such as Lawrence Berkley National Laboratory’s THERM calculate two-dimensional heat transfer.³³ This method may be used for most above-grade wall assemblies; however, it is not appropriate for assemblies where intermittent fasteners, anchors, or cladding supports bridge exterior insulation. An example of a two-dimensional thermal image produced from this modeling approach is shown in Fig. 8-8.
Three-Dimensional Computer Modeling: Programs such as HEAT3 calculate three-dimensional heat transfer.³⁴ This method may be used for all above-grade assemblies, including those with exterior insulation bridged by fasteners. An example of a three-dimensional thermal image produced from this modeling approach is shown in Fig. 8-11.
Heat Transmittance Coefficients: Linear heat transmittance coefficients (ψ-values) factor in the heat flow through a wall attributed to a linear thermal bridge (e.g., a continuous shelf angle). Point heat transmittance coefficients (χ-values) similarly factor the attributed heat flow from intermittent or point thermal bridges (e.g., a fastener). These factors can then can be superimposed onto the clear wall assembly U-factor to obtain the effective wall U-factor. The clear wall assembly U-factor is defined as the U-factor for the enclosure area containing only insulation and necessary framing materials for a clear section with no fenestration, corners, penetrations, or connections between other enclosure elements such as roofs, foundations, and other walls. Tabulated linear and point heat transmittance coefficients can be found in ISO 14683:2017 Thermal Bridges in Building Construction, ³⁵ in the Building Envelope Thermal Bridging Guide, ³⁶ and from manufacturers of proprietary structural systems.

Within the following section, three-dimensional computer modeling was employed to demonstrate how typical thermal bridges in masonry assemblies—like masonry anchors, shelf angles, and wall framing—contribute to the effective thermal performance of wall systems for design and analysis purposes.

Masonry System Thermal Performance Design Tables

While there are various methods available for calculating the effective U-factor of a masonry wall system, accurately assessing the thermal performance of systems with highly conductive thermal bridges such as anchors can be complex and time-intensive, particularly when intermittent steel clips, anchors, or fasteners interrupt an insulation layer. The simplest method for determining thermal performance is to use tabulated values from industry-accepted sources, such as ASHRAE 90.1 Appendix A.³¹ These values, however, may not be appropriate where the U-factors for masonry veneer wall systems with specific types of anchors and shelf angle options are being considered or must be known.

This section presents effective R-values for exterior-insulated anchored masonry veneer wall systems and interior-insulated CMU wall systems determined through three-dimensional thermal modeling. There is no industry-standard definition for the term effective R-value. This guide uses this term to refer to the assembly R-value inclusive of all wall layers, air films, and thermal bridging.

Using the Design Tables and Figures

Modeling results presented within this guide can be used to estimate project-specific thermal performance requirements for anchored masonry veneer wall systems and interior insulated single-wythe CMU wall systems.

Anchored masonry veneer wall system results are organized by four backup wall structures:

8-inch CMU wall
35 ⁄8-inch steel stud-framed wall with R-15 batt insulation
6-inch steel stud-framed wall with R-21 batt insulation
51 ⁄2 inch wood-framed wall with R-21 batt insulation

For each backup wall structure, effective R-values are presented for different combinations of masonry anchor systems, shelf angle configurations (continuous or standoff), and exterior insulation thickness.

Single-wythe CMU wall system results are organized by interior insulation approach:

R-12 cavity insulation
R-12 cavity insulation with R-12 continuous insulation
1-inch XPS insulation between framing and CMU
R-12 continuous insulation
R-24 continuous insulation
R-24 cavity insulation
R-15 batt cavity insulation with 2-inch XPS between framing and CMU
R-15 batt cavity insulation with 3-inch XPS insulation between framing and CMU

For all wall systems, the effective R-values in the table results are presented as a range, with the lower value representing an insulation with a resistance value of R-4.2 per inch and the upper value representing insulation with a resistance value of R-6 per inch. To estimate the thermal performance for exterior values between R-4.2/inch and R-6/inch, the lower and upper range values can be linearly interpolated within an accuracy of 1%. Refer to the Linear Interpolation sidebar of page 138 for the linear interpolation equation and an example calculation.

Anchored masonry veneer wall system results are also graphically presented for backup wall type for ease of interpolation and to visualize the relative thermal degradation of different anchor systems.

Modeling specifics and additional information used to complete the modeling within this guide are provided in Appendix A.

Thermal Modeling Results: CMU Backup Wall With Anchored Masonry Veneer

The modeled system includes the components depicted graphically in Fig. 8-14:

8-inch medium weight single-wythe CMU wall
3, 4, and 5 inches of R-4.2/inch or R-6 per inch exterior insulation
Air cavity
Anchored masonry veneer

Anchor types are considered at 16 inches by 16 inches spacing for results where exterior insulation is not assumed to be continuous. Modeled anchor types include:

Ladder eye-wire anchor (3 ⁄16-inch diameter) with cross-rods at 16 inches on-center made of hot-dipped galvanized steel or Type 304 stainless steel. Hooks are either hot-dipped galvanized steel or Type 304 stainless steel to match the ladder wire.
Thermally optimized screw anchor with stainless-steel barrel and carbon-steel fastener. Hooks are either hotdipped galvanized steel or Type 304 stainless steel.
Double eye and pintle plate anchor (14-gauge). Hooks are either hot-dipped galvanized steel or Type 304 stainless steel to match the anchor plate.

Modeling results consider a concrete slab bypass condition with and without hot-dipped galvanized-steel shelf angles. Shelf angles are either attached tight to the floor line structure (continuous shelf angle) or offset to the depth of the exterior insulation and supported by intermittent hollow steel sections (HSS) at 4 feet on-center (standoff shelf angle).

Linear Interpolation

Effective R-values in this guide can be interpolated for assemblies with exterior insulation with thermal resistances between R-4.2/inch and R-6/inch from tabulated results using the equation below:

Where:
R-EFF = Effective R-value for specific assembly in question by interpolation
R-NOM = Nominal R-value of the specific assembly in question
R_4.2-NOM = Nominal R-value from lower range in design tables (i.e., R-4.2/inch exterior insulation)
R₆-NOM = Nominal R-value from upper range of design tables (i.e., R-6/inch exterior insulation)
R_4.2-EFF = Effective R-value from lower range in design tables (i.e., R-4.2/in exterior insulation)
R₆ -EFF = Effective R-value from upper range in design tables (i.e., R-6/in exterior insulation)

Example:

2×6 wood frame with R-21 batts and 1-inch R-5/in exterior insulation, thermally optimized screw tie with stainless hook, no shelf angle:

R-NOM = R-21 + R-5 = R-26
R4.2-NOM = R-21 + R-4.2 = R-25.2
R6 -NOM = R-21 + R-6 = R-27
R4.2-EFF = R-22.2
R6 -EFF = R-23.8

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Thermal Modeling Results: Steel Stud-Framed Wall

The modeled system includes the components depicted graphically in Fig. 8-17:

Interior gypsum board
35 ⁄8-inch steel studs at 16 inches on-center (including the top and bottom track of a full-height wall) or 6-inch steel studs at 16 inches on-center (including the top and bottom track of a full-height wall)
R-15 (with 35 ⁄8-inch steel studs) or R-21 (with 6-inch steel studs) batt insulation
Exterior gypsum sheathing
2, 3, and 4 inches of R-4.2 or R-6/inch exterior insulation
Air cavity
Anchored masonry veneer

Anchor types are considered at 16 inches by 16 inches spacing where exterior insulation is not continuous. Modeled anchor types include:

Thermally optimized screw anchor with stainless-steel barrel and carbon-steel fastener. Hooks are either hot-dipped galvanized steel or Type 304 stainless steel.
Double eye and pintle plate anchor (14-gauge). Hooks are either hot-dipped galvanized steel or Type 304 stainless steel to match the anchor plate.

For this wall system, shelf angle supports will typically occur at the periphery of concrete slab edges, such as that shown in Fig. 8-16 a and b. The slab-edge would be classified as an above-grade mass wall and can be considered as a separate assembly from the steel stud-framed wall for energy code compliance purposes.

For this reason, the concrete floor line shelf angle assembly was modeled separately from the steel stud-framed wall. In the concrete floor line shelf angle assembly presented in Table 8-7, hot-dipped galvanized-steel shelf angles are either attached tight to the concrete floor line structure (continuous shelf angle) or off-set to the depth of the exterior insulation and supported by intermittent hollow steel sections (HSS) at 4 feet on-center (standoff shelf angle). Floor line modeling results consider the effects of the steel stud-framed system above and below.

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Thermal Modeling Results: Wood-Framed Wall

The modeled system includes the components depicted graphically in Fig. 8-20: 1. Interior gypsum board
2×6 wood studs including the top and bottom plates of a full-height wall (23% framing factor) with R-21 batt insulation
Exterior plywood sheathing
1, 2, and 3 inches of R-4.2 or R-6/inch exterior insulation 1-inch air cavity
Air cavity
Anchored masonry veneer

Anchor types are considered at 16 inches by 16 inches spacing where exterior insulation is not continuous. Modeled anchor types include:

Thermally optimized screw anchor with stainless-steel barrel and carbon-steel fastener. Hooks are either hot-dipped galvanized steel or Type 304 stainless steel.
Double eye and pintle plate anchor (14-gauge). Hooks are either hot-dipped galvanized steel or Type 304 stainless steel to match the anchor plate.

Modeling results consider a full-height wall with a wood-framed floor line condition. Hot-dipped galvanized-steel shelf angles are either attached tight to the floor line structure (continuous shelf angle) or offset to the depth of the exterior insulation and supported by intermittent hollow steel sections (HSS) at 4 feet on-center (standoff shelf angle).

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Thermal Modeling Results: Interior-Insulated Single-Wythe CMU

The modeled system includes an 8-inch medium-weight CMU block and eight configurations of interior insulation as as depicted graphically in Fig. 8-23. Interior wall framing is provided by galvanized steel studs at 16-inches on-center, including a top and bottom track. Options 1, 3, and 4 were modeled with the wall framing offset from the CMU wall structure to allow clearance for a continuous insulation layer. The remaining options were modeled with wall framing tight to the CMU wall structure. Cavity insulation is either R-15 batt isulation or R-6/inch insulation, such as CCSPF. Continuous insulation is either R-5 or R-6/inch, typical R-values for either rigid XPS or CCSPF insulation respectively.

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Chapter References

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