Evaluating Metal Building Systems Using COMcheck™  

Metal building systems typically account for about one-quarter of all the low-rise commercial construction in the United States each year. These systems have evolved in the past few decades and are now fully capable of meeting and exceeding energy code requirements in all climate zones of the United States. However, there is often some confusion about the make-up of the wall and roof assemblies, what the options are, and how they impact energy code compliance. COMcheck™ is a widely used software tool to demonstrate energy code compliance that is fully customizable to suit different project requirements, including metal buildings. The software is available for free from the U.S. Department of Energy and includes all of the options in the codes, relying on the building designer to input the appropriate information. It then calculates the overall energy performance of the building envelope to determine if the design meets the code requirements or not by using the envelope trade-off method. This course looks specifically at the benefits of using COMcheck™ for metal building system designs and addresses some of the most common questions and uncertainties that architects may have related to metal buildings and energy performance.

Photo courtesy of Metal Building Manufacturers Association

Metal building systems can be readily designed to meet energy codes, as is easily proven by using COMcheck^TM software.

METAL BUILDING SYSTEMS OVERVIEW

Metal building systems are offered by manufacturers who generally provide a complete package of products and services for a custom-engineered structure, which can take one of two forms. First, they can be the single source for a total metal building system, which is a complete package of products, and services for both the structural system and the primary building envelope components, such as exterior wall and roof assemblies. That means the total building structure and envelope are designed, specified, and assembled using components that are custom fabricated according to the design prepared by the building’s architect of record. The primary steel structure consists of main columns, beams, or engineered rigid frames while the secondary steel structural components include girts, purlins, etc. for rigidity and attachment of wall and roof systems. The envelope typically consists of metal wall systems (metal panels, insulated or not) plus metal roof systems or panels that are designed to meet project specifications.

The second form of a metal building system is a combination or a hybrid building that can be designed and built by incorporating only some of the systems from a metal building manufacturer such as the primary and secondary structural portion. In this case, the wall and roof envelope assemblies are constructed from traditional building materials and methods such as concrete, masonry, wood, glazing systems, etc. As such, the finished building can look, feel, and perform like any traditional building. For existing buildings, it is possible to retrofit only metal siding and/or metal roofing on top of or in place of existing wall and roof assemblies. Some manufacturers may also provide supporting products and materials such as insulation, fenestration, roof curbs, and doors for use in either a total metal building system or a hybrid one.

The use of metal building systems has become so common that the 2024 International Building Code (IBC) now recognizes them with this definition: “An integrated set of fabricated components and assemblies that form a complete or partial building shell that is designed by the manufacturer. This system typically includes, but is not limited to, primary framing composed of built-up structural steel members, secondary members that are cold-formed steel or open-web steel joists, a metal panel roof system, and exterior wall cladding. The system is manufactured in a manner that permits plant or field inspection prior to assembly or erection.”

Once the specified package is fabricated to order, it is shipped to the project location for on-site erection and installation, typically by an independent erector/installer or general contractor. With this working model as a basis, it is easy to see that it is more streamlined and usually more cost-efficient to design and construct a single-source metal building compared to conventional, multiparty construction.

Photo courtesy of Metal Building Manufacturers Association

The basic elements of a total metal building system include the primary and secondary steel structure plus the basic envelope including metal roofing, metal siding, and, sometimes, the insulation.

Significant Attributes

Metal building systems are a distinct type of construction for low-rise buildings with a number of appealing attributes. The structural system offers complete design flexibility including the option for longer clear spans, often using built-up tapered-web members, compared to traditional steel framing (i.e., hot-rolled steel beams, columns, etc.) thus creating very open spaces. The structure and the rest of the system designs are optimized to provide efficient use of materials while minimizing waste. The process of working with a metal building manufacturer typically allows for a faster design process, streamlined fabrication, and a shortened construction process when compared to conventional construction. All of these traits help keep the cost of metal buildings very competitive and quite favorable in many instances.

Typical Metal Building Wall Systems

One thing that distinguishes metal building systems is the variety of wall systems that are possible. Since the structural steel frame bears the load, there are options for architectural or industrial metal walls, brick, glass, wood, masonry, EIFS, tilt-up, insulated metal wall panels, or other materials.

When the wall assemblies are provided by a metal building manufacturer, they typically come in a form aligned with one of the ASHRAE 90.1 wall assembly types defined in the Normative Appendix, Section A3.2.2. Those assembly types include:

• Single-Layer Compressed, where a single layer of insulation is compressed between the girts and metal panels. Special cases can include thick or multiple layers of insulation, but care must be taken to avoid oil canning of the metal panels.
• Single-Layer in Cavity, where a single layer of insulation is installed in the cavity between the girts that is not compressed by the metal panels. This can be a faced layer of insulation or can be unfaced insulation with a separate facing installed inside the girts. Thermal spacer blocks or thermal break strips may be required between the girts and metal panels if required in Table A3.2.3 or the proprietary assembly test or modeling report.
• Double-Layer, where one layer of insulation is installed in the cavity between the girts and a second layer is installed between the girts and metal panels. Thermal spacer blocks or thermal break strips may be required between the girts and metal panels if required in Table A3.2.3 or the proprietary assembly test or modeling report.

Other assemblies like continuous insulation or proprietary systems may also be used. Most of these wall assemblies are compatible with using gypsum board or other common interior wall finishes.

Another option for walls is to use a fabricated insulated metal panel (IMP) which incorporates rigid insulation sandwiched between an inner and outer metal facing to form a composite panel. This type of product is pre-insulated and has appeal in many building applications since both the exterior and interior surfaces are pre-finished and can be detailed to meet air and vapor transmission requirements. It should be noted, however, that IMPs do not meet the definition of “continuous insulation,” since the panel edges intrude within the foam sheathing insulation. However, the U-factor of an IMP assembly may be adequate to negate the need for continuous insulation. Furthermore, IMP designs can provide fairly good insulation values per inch of thickness when used properly.

Typical Metal Building Roof Systems

It is most common for a metal building system to use metal roofing. This is in part because they allow for a low roof slope (less than 2:12) and external drainage (rather than interior drains) which coordinates well with the structural system. It is also quite desirable because of the proven longevity of standing seam metal roofing which is often rated for 50 years or more. Underneath the metal roof panels, insulation can be handled in a manner similar to walls. When the roof assemblies are provided by a metal building manufacturer, they typically come in a form aligned with one of the ASHRAE 90.1 roof assembly types defined in the Normative Appendix, Section A2.3.2. Those assembly types include:

• Single-Layer [Compressed], where a single layer of faced insulation is compressed between the purlins and metal roof panels. Special cases can include thick or multiple layers of insulation, but care must be taken to avoid oil canning of the metal panels. A thermal spacer block may be required between the purlins and metal roof panels.
• Double-Layer, where faced insulation is draped over and perpendicular to the purlins, and a second layer of unfaced insulation is installed above the first layer of insulation and parallel to the purlins. A thermal spacer block may be required between the purlins and metal roof panels. This may commonly be referred to as a Sag-N-Bag system.
• Liner System (LS), where one layer of uncompressed, unfaced insulation is installed in the cavity between the purlins, and a second layer of unfaced insulation is installed and compressed between the purlins and metal roof panels. A vapor retarding fabric liner is attached to and supported below the purlins. Thermal spacer blocks may be required between the purlins and metal roof panels if required in Table A2.3.3 or the proprietary assembly test or modeling report.

Other assemblies like continuous insulation or proprietary systems may also be used. Air and vapor control can typically be addressed easily with tapes and sealants between facings or liners. In several cases, the exposed insulation facing or liner can create a finished ceiling. Alternatively, a conventional system can be suspended down into the space below. As with walls, insulated metal panels are an option, but they do not qualify as continuous insulation.

Photo courtesy of Therm-All and the Metal Building Manufacturers Association

The insulation approach of a metal building system can include single or double layers of insulation with full air sealing and vapor retarder protections.

Typical Foundation Systems

Metal building system manufacturers don’t provide foundations. Rather they provide an anchor rod plan and the structural engineering reactions for an architect or engineer to design the foundation to be built on-site accordingly. For most low-rise buildings, that usually means a concrete slab on grade, but any type of conventional foundation and first-floor system can be used to support a metal building system. The insulation of the foundation will need to be detailed as with any building and the installation will need to be inspected and verified before the metal building system is assembled and constructed.

THE ENERGY CODE AND COMPLIANCE

The International Energy Conservation Code (IECC) is part of the family of codes that are created, managed, and regularly updated by the International Code Council. It does not exist to regulate energy consumption (i.e., there are no violation orders issued if a monthly utility bill is too high), but to regulate the design and construction of buildings so that energy usage in buildings is better controlled. That control falls into two categories: 1) energy conservation, which is the act of reducing the amount of energy needed in the first place, particularly by addressing the building envelope (insulation, air sealing, glazing traits, etc.); 2) energy efficiency, which means reducing the amount of energy required to power mechanical and electrical equipment such as heating, cooling, lighting, etc. and still achieve the desired outcomes (thermal comfort, proper light levels, etc.). Taken together, we refer to the energy performance of a building as a combination of conservation and efficiency measures that achieve a measurable outcome.

The IECC addresses all of these aspects of energy performance. It also recognizes that eight different climate zones exist around the country that directly impact the energy performance in buildings. Therefore, the provisions are broken down by particular building construction components (building envelope, mechanical systems, etc.) but the specific requirement to show code compliance can vary depending on the climate zone where the building is located. The commercial buildings part of the IECC also recognizes different standard construction systems and assemblies, including recognition of metal building systems as a conventional building type. Therefore, when addressing a provision of the IECC in design, it is necessary to look specifically at the requirements for the climate zone and for the relevant construction systems used in the building.

Photo courtesy of Therm-All and the Metal Building Manufacturers Association

The insulation for roofs in metal building systems can be achieved effectively in a similar manner to walls with options for the amount and type of insulation used.

Compliance Path Option

The IECC, like all codes, sets the minimum standard for performance but does not endeavor to design the building – that is the purview of the licensed design professionals. In that light, the code recognizes that there is more than one way to achieve the required energy performance results depending on the overall design of the building. Therefore, it is possible to show compliance with the IECC in any one of three ways:

• Prescriptive Requirement Path This is the most direct and straightforward means of compliance, although it may or may not be the preferred way to design a building. Showing compliance with the IECC by prescription means that all defined components (wall assemblies, roof assemblies, openings, etc.) are designed and installed as prescribed in the IECC. Tables in the code simply state the minimum R-values or maximum U-factors for different building components that must be met as prescribed, based on the type of component and the climate zone. In this case, the construction assemblies are presumed to be standard, including those for metal building systems. Since the general construction system is presumed to be standard, note that the R-values in the tables refer only to the insulation (not the entire assembly) at the minimum performance level that must be installed, including some requirements for continuous insulation in certain climate zones. There is an alternative to use prescriptive tables based on U-Factors for entire wall and roof assemblies in which case it is incumbent on the designer to demonstrate and prove how the proposed assembly achieves those prescribed U-factors. Therefore, if the wall, roof, and other assemblies are very standard, this prescriptive path may be fairly easy to work with, but many building professionals find it rather restrictive and potentially more difficult to design and construct, particularly where continuous insulation is concerned.
• Building Envelope Trade-off Path In this second means of showing compliance with the IECC, there is an allowance for looking at the overall performance of the combined energy conservation measures including building envelope insulation levels and glazing/opening performance. Essentially, that means some trade-offs are possible where one area of the building can readily exceed the prescriptive minimum (i.e., in the roof assembly) and make up for another area that may fall short (i.e., in the wall assembly or glazing). (See section C101.5.1 of the IECC) Note that this trade-off is limited to the building envelope thermal performance only and does not apply to prescriptive air infiltration requirements or efficiency measures for mechanical and electrical equipment, all of which must still be met.

The means to show compliance in this path is based on determining the U-factors for an entire assembly and considering the area (in square feet) of that assembly relative to the entire building. Since it is essentially based on U-factor multiplied by the area, it is commonly abbreviated as the UxA or simply the UA method. It is possible to do this calculation by hand, but it is much easier and faster to do it using the COMcheck™ software. It is commonly reported by code enforcement officers that the overwhelming majority of projects (over 90 percent in some locations) use the building envelope trade-off method of showing IECC compliance. Almost all of those use COMcheck™ as the way to calculate and show that compliance.

• Performance Path In some cases, a building designer wants to take all of the conservation and efficiency measures into account and look at the total performance. The IECC allows for this if a full, computerized energy model of the total building performance is prepared and presented according to the stated requirements of the code. In this case, a computerized baseline model must be created as if the building met all of the prescriptive requirements. Then a second computer model is prepared adjusting only those things that are different from the prescribed minimum for the envelope energy conservation and the electrical and mechanical efficiency as designed. The two models are compared and if the proposed design exceeds the performance of the baseline, then it passes. This is obviously a more involved process and usually only undertaken on buildings that either can’t readily show compliance using one of the other paths or if exceptional performance is being sought to meet a higher overall standard than the code such as for LEED, ENERGY STAR, or other building standards.

When designing any building, including a metal building system, the first step in showing compliance with the IECC is to choose which of the three paths described above will be used.

ASHRAE 90.1 and the IECC Section

While the IECC is very specific about construction requirements, it also recognizes that there are other standards that can be used as well. In particular, ASHRAE 90.1 “Energy Standard for Buildings Except Low-Rise Residential Buildings” is referenced in the IECC and has been recognized as a standard that is “equivalent” to, albeit not identical to, the requirements of the IECC. Hence, Section C401.2 of the IECC lists ASHRAE 90.1 as an approved method to use when showing code compliance for commercial, industrial, and institutional (i.e., non-residential) buildings. While there are indeed differences between ASHRAE 90.1 and the IECC, a building designed to meet the minimum standard of either one should yield approximately the same overall energy performance. Based on this, building designers can choose to use the thermal requirements of either IECC or ASHRAE 90.1 to show energy code compliance. However, if selected, ASHRAE 90.1 must be used to show compliance for the entire building including air infiltration and for mechanical and electrical systems. Note that in some jurisdictions, such as New York City, the only recognized choice for commercial building compliance is to use ASHRAE 90.1, not the IECC. In certain other cases, ASHRAE 90.1 may be the best choice such as for semi-heated spaces (e.g., a warehouse or similar), where the IECC provides no provision for compliance.

In terms of using the ASHRAE 90.1 method, note that it has the same three options for showing compliance – prescriptive, envelope trade-off (using COMcheck™), or performance (energy model), although some details of each are a little different. In either case, ASHRAE 90.1 includes tables of different prescriptive assemblies with their respective U-Factors calculated. These calculated assemblies are recognized for use in both ASHRAE 90.1 and the IECC, meaning that the designer does not need to re-create them, rather, just reference the appropriate assembly. This is particularly useful for metal building systems since there are a range of wall and roof assemblies that are already identified and calculated making it easier to work with and show compliance.

Photo courtesy of International Code Council and ASHRAE

The International Energy Conservation Code and ASHRAE 90.1 both offer three different ways or paths to demonstrate compliance.

USING COMCHECK™ AS A CODE COMPLIANCE TOOL

As noted, COMcheck™ is a very popular, free software tool from the US Department of Energy. (See https://www.energycodes.gov/comcheck ) While it is currently available for download or use online, it is expected to be an online-only tool in the near future. It is commonly recognized as an acceptable, even preferred, energy code compliance tool in most U.S. jurisdictions, even if not explicitly stated as such.

Right up front, it is important to be aware that the software allows for complete customization to suit the particular building being assessed. All of the upfront defining information such as location, building type, designers, owners, etc. needs to be entered in. It then has built-in options to select the specific energy code and version being used such as the specific year of the IECC, ASHRAE 90.1, or another recognized state variation. It also requires that the project location, which determines the climate zone, is identified.

With all of this basic information established and verified by the user, then the specifics of the building can be entered. That will require a separate identification of the different assemblies for walls, roofs, floors, and openings such as windows, doors, and skylights. The area in square feet of each assembly or component will need to be determined ahead of time based on drawings or a CAD/ BIM file. (There is COMcheck™ guidance and instructions on how to properly do so). Then each assembly needs to be identified with the corresponding R-value(s) or U-factor. The most effective way to do that is to use the pull-down menus in COMcheck™ and select the appropriate predetermined assembly. This is particularly true for metal building systems and makes the process not only easier but also more accurate in terms of calculation.

Once all of the appropriate data is put in for the envelope, the on-screen “Check Compliance” button needs to be selected. This action triggers the software to calculate the thermal performance and delivers a result in terms of a percentage better than or worse than the prescriptive requirements. If the result is positive, then compliance is demonstrated, and the project is ready to move ahead. If it is negative, then the person doing the information input should double-check the data entered to be sure there are no mistakes, and, if there aren’t, then some aspect of the building envelope needs to be rethought or redesigned to achieve compliance. That may be as simple as choosing more energy-efficient windows and doors or it may require selecting a higher-performance wall or roof insulation system. For metal building systems, it is always worth checking the floor system insulation and details as well since a simple increase in the insulation there may make a big difference. Of course, whatever is entered in the COMcheck™ program needs to be supported by updated construction drawings and needs to be readily available to the building code inspector for verification in the field.

Photo courtesy of U.S. Dept. of Energy

COMcheck™ is an easy-to-use, free software program from the U.S. Department of Energy that is commonly used to show compliance with the energy codes.

Understanding COMcheck™ Inputs

When using COMcheck™, it is not unusual for several questions or concerns to pop up. Some of the common general ones related to U-factors and thermal performance of metal buildings are summarized below. Note that these are based on the 2021 IECC and ASHRAE 90.1-2019.

Why didn’t anything change for the U-factor when I increased the R-value?

For pre-approved assemblies, COMcheck™ doesn’t give additional credit for R-values above certain limits. You should have seen a “pop-up” alert that notified you of this situation. The message might have been something like, “For Metal Building, Standing Seam: Liner System with Thermal Blocks assemblies, ASHRAE Standard 90.1-2019 does not give additional credit for cavity R-values above R-47.” U-factors for metal building roof and wall assemblies can be found in ASHRAE Standard 90.1-2019 Tables A2.3.3 (roofs) and A3.2.3 (walls).

Where can I get U-factors for pre-approved assemblies?

Normative Appendix A in ASHRAE Standard 90.1-2019 has tables and other information regarding R-values and equivalent assembly U-factors for a wide variety of metal building roof and wall assemblies. Metal building assemblies are found in Tables A2.3.3 and A3.2.3. For a hybrid building, other applicable construction types of roof and wall assemblies, are available in other Normative Appendix A tables. Alternatively, a proprietary system that is tested in accordance with ASTM C1363 (Hot Box Test) or thermally modeled can be used. Refer to ASHRAE Standard 90.1-2019 Normative Appendix A9 for requirements for all “alternative U-factors.” When using such a system, use the “Other U-Factor Option” tab in COMcheck™ and insert the U-factor. A pop-up will advise you to supply the data for the U-factor used.

If I enter the U-factors from Normative Appendix A from ASHRAE Standard 90.1, do I need anything more for the building official?

Normative Appendix A is part of the standard and therefore does not require a request for alternative means and methods to use the contents to demonstrate compliance. It will be helpful for the code official to reference the particular table or section and the specific year edition of ASHRAE Standard 90.1 as the source of the U-factors. Another option is to select an applicable system type from the drop-down menu and enter the nominal R-value for the assembly, then the building official knows that it came from the pre-published tables (and limits possible errors), e.g., enter Liner System with R-47 in the Insulation R-value column for R-25 + R-11 + R-11 Liner System.

Do I have to use continuous insulation (c.i.) to comply with the IECC?

The answer is it depends. If you are seeking to comply with the specific prescriptive R-value requirements in the 2021 IECC and “c.i.” is present in the prescriptive requirements, then “Yes.” If you are seeking to comply with the specific U-factor requirements in the 2021 IECC, then you only have to use continuous insulation if the selected metal building assembly requires continuous insulation to achieve the applicable U-factor.

Do Insulated Metal Panels (IMPs) satisfy the prescriptive continuous insulation (c.i.) requirement?

IMPs do not qualify as continuous insulation because the metal return side-joinery, located at the IMP joints that returns into the insulation, creates a “break” in the continuity of the insulation and a partial thermal bridge, is considered as not complying with the requirements for continuous insulation. However, only in the ASHRAE 90.1-2022 edition are IMPs recognized as a cladding. The IMPs can be associated with any of the roof or wall categories to demonstrate compliance with the building envelope requirement tables maximum U-factors. Insulated metal panels are defined as: “a factory-manufactured panel consisting of metal facings an insulative core, and panel joint intended for use in an assembly forming an exterior wall, an exterior wall covering, or a roof covering of a building envelope.” (Source: ASHRAE © 2022).

Do thermal spacer blocks satisfy the prescriptive continuous insulation (c.i.) requirement?

No, because the thermal spacer blocks are not continuous across the entire assembly; installation of continuous rigid board insulation is typically the best method for satisfying the c.i. requirement.

Do I have to use thermal spacer blocks or thermal break strip to comply with the IECC?

If you are seeking to comply with the specific prescriptive R-value requirements in the 2021 IECC, then “Yes”. If you are seeking to comply with the specific U-factor requirements in the 2021 IECC, then you only have to use thermal spacer blocks or thermal break strip if the selected assembly requires them for the applicable U-factor.

Photo courtesy of Metal Building Manufacturers Association

Continuous insulation, where required or used, must be truly continuous across all framing members to prevent thermal bridging between the interior and exterior of the building.

Metal Building Wall Systems and COMcheck™

Opaque envelope wall assemblies are part of all buildings and ASHRAE-approved standard metal building wall assemblies are included in COMcheck™. These are the easiest to use when the building design matches them. Of course, many metal building system designs use other wall finishes or construction other than standard metal building system options. In this case, the user would select the appropriate wall construction system (e.g., metal studs, masonry, etc.) and select those from the ASHRAE assemblies. In the case where none of the standard assemblies match the design proposed, then thermally modeled or tested assemblies can be input for the wall systems. The building official will need to be provided with documentation of the results of the model or testing in this case.

Beyond the opaque wall areas, a significant design feature of most commercial buildings is the glass and glazing that is incorporated into a building envelope. There are many variables related to their design such as the type, size, shape, color, and configuration of the glazing, which often receive plenty of attention. There are also many variables that affect the performance and the energy code compliance of the glazing system including the percentage of glazed to opaque wall areas, the number of layers of glass, the type of glass used, glass treatments or coatings, the framing system that holds the glass, and even the type of spacers between double- or triple-paned products. It is important to recognize that all of these variables are essentially different components of a glazing system that can be controlled and specified to suit specific project conditions, climate zones, and code requirements. It is not about any one item alone (i.e., the framing system or the glass) but the entire make-up of all of them. If pre-manufactured glazing products are used, then they often come with third-party verified U-factors, solar heat gain coefficient (SHGC), and visual transmittance (VT) data that can be used in COMcheck™ calculations. If the glazing is provided by a metal building manufacturer, they should be able to provide the needed information. Conversely, the size, area, and configuration are all purely the purview of the building designer. All of the same things apply to any doors in the building, whether for the movement of people or large overhead doors for moving equipment and vehicles. Thermal values can be obtained from the manufacturer’s tested results while the size, shape, and layout are all a matter of design.

Some common questions and answers related to metal building system walls include the following:

Do I have to enter doors and windows individually or is there a more efficient method to input doors and windows?

Common door types and common window types can be “grouped” together and entered by total square feet for each individual wall surface.

How do I input “louvers?”

Louvers are generally considered to be uninsulated areas. However, there is an allowance for up to 1 percent of wall area in “recessed equipment” in walls in ASHRAE Standard 90.1-2019.

I don’t know what kinds of windows or doors are going to be used for my building yet, what do I do?

You can either use the unlabeled (code default) values in the 2021 IECC or ASHRAE Standard 90.1-2019 Normative Appendix Sections A7 and A8, or you can make conservative assumptions as to the types of windows and doors that will be installed. Code defaults assume very low-performing windows and doors and can cause the design to fail compliance. It is best to get actual data from the manufacturers.

Photo courtesy of Therm-All and the Metal Building Manufacturers Association

High-performance thermal walls in metal building systems can be designed and incorporated into COMcheck™ to show the needed level of energy conservation.

Metal Building Roof Systems and COMcheck™

Insulated roof assemblies can be a significant determinant in the energy performance of metal building systems. This is particularly true for a large building, such as retail or warehouse buildings, where the roof area is generally equal to the floor area and the exterior walls are relatively small in comparison. (This is in contrast with a tall building where the roof area may be very small compared to the extensive vertical wall area.) As with walls, using the ASHRAE-approved standard metal building roof assemblies included in COMcheck™ will be the easiest to use where the building design matches them. Otherwise, custom systems can be designed and specified using their respective published or tested thermal values.

Metal roofs also have some other characteristics that are worth noting in terms of energy performance. The first is in relation to “cool roof” requirements where they might be mandated or needed to reduce the heat generated by undesirable solar heat on a dark-colored roof. Cool roof performance is a function of two radiative properties. The first is solar reflectance (SR) which is defined by the Cool Roof Rating Council (CRRC) as, "The ratio of the reflected flux to the incident flux." In other words, it represents the fraction of light reflected off the roof. For example, "high" reflectance materials, such as white-painted metal roofing, have values of around 0.70 (a.k.a. 70 percent). That is, only 30 percent of the light from the sun is retained by the roof. The second cool roof property is infrared or thermal emittance (TE), defined by CRRC as, "The ratio of the radiant heat flux emitted by a sample to that emitted by a black body radiator at the same temperature." In plain terms, emittance is a decimal number less than one that represents the fraction of heat that is re-radiated from a material to its surroundings. Metal roofs can help keep this number low as well.

The second characteristic of metal roofs is that they can be easily used for “solar ready” and “net zero” roof options. Standing seam metal roofing makes it very easy to attach clamps or clips that do not penetrate the roofing but are quite strong and capable of attaching a solar photovoltaic array. This feature may, in some cases, be a code requirement, or it may help meet other needs of the building owner or for voluntary standards such as LEED.

With all of the above in mind, here are some common questions that can arise when addressing metal roof systems and the energy codes:

Do I have to use a Standing Seam Roof (SSR) to comply with the IECC?

If you are seeking to comply with the specific prescriptive R-value requirements in the 2021 IECC, then “Yes.” However, any assembly that has a satisfactory U-factor complies. Alternatively, some assemblies with U-factors less than the maximum may work if using trade-offs.

Is there any way for a through-fastened roof system to comply with the energy code?

A screwed-down roof in ASHRAE is defined as a through-fastened roof. Depending on the climate zone, and whether the building is conditioned or semi-heated, there are insulation systems, such as continuous insulation and liner system assemblies, that can meet the code based on published U-factors in ASHRAE 90.1-2019 Table A2.3.3. In some cases, COMcheck™ will allow a through-fastened roof to pass by installing additional insulation in the walls. Other proprietary systems are available, which have U-factors determined by testing that equal or exceed the code requirements.

Photo courtesy of Therm-All and the Metal Building Manufacturers Association

Roof systems can also achieve high thermal performance through the proper detailing and selection of metal roofing system assemblies.

Floor Systems in Metal Buildings

As noted previously, insulated floors can make a big difference in showing compliance with the energy code. It is important to remember that the floors are calculated in COMcheck™ as well as the roof and wall systems. The specific type of floor system and the amount and location of the insulation can be selected in the COMcheck™ program with the corresponding square footage added in. In the case of floor slabs, the vertical edge insulation will be as important as the horizontal under-slab insulation that is used, and both need to be entered. If the building incorporates a heated slab, then continuous insulation under the slab is required at minimum levels, although more is always an option too. For other types of floor systems, the appropriate vertical or horizontal insulation needs to be entered along with the thermal value of the insulation.

Paying attention to the floor insulation can be significant in terms of showing compliance, particularly if the building has a large floor area. This may be an area that can effectively offset a shortfall somewhere else, such as one with many overhead doors or other penetrations in the walls.

Photo courtesy of Therm-All and the Metal Building Manufacturers Association

Semi-heated buildings can be treated differently under ASHRAE 90.1 when the interior spaces do not meet the definition of a fully conditioned space.

OTHER COMMON COMCHECK™ QUESTIONS RELATED TO METAL BUILDINGS

With an understanding of the basics of metal buildings systems, the energy code options, and COMcheck™, the following list of questions and answers address some of the other common experiences of building professionals who have used them all.

What are the requirements for submitting a COMcheck™ Compliance Certificate?

COMcheck™ can be performed by any qualified person, but the report may need to be signed by a registered design professional according to the jurisdiction. See Section C103.3, Examination of Documents, of the 2021 IECC.

My building is located in a region not listed in the COMcheck™ drop-down menu, what do I do?

You should follow the adopted code in effect for that area or region. According to COMcheck™, choose a city, town, or region that is the closest within the same Climate Zone. Call the authority having jurisdiction to verify the requirements.

I’m adding onto an existing building that met an older edition of the energy code; what code do I use for the addition?

The adopted code in effect will have provisions as to how to handle the addition to, or alteration of, an existing building envelope. Both the 2021 IECC and ASHRAE 90.1-2019 have specific provisions to address additions, alterations, and even repairs. In most cases, the new work needs to meet the current energy code requirements, but areas not affected by the new work do not need to be upgraded.

Is a “Barndominium” a residence or a commercial building?

A barndominium is a term that combines the terms "barn" and "condominium" and describes barn construction being used for any occupancy other than agriculture. It is a marketing term not found in most energy, building, or residential codes. One should refer to the adopted codes in effect, or contact the authority having jurisdiction, to verify the occupancy type for that building or the space within.

Can a building that has some air-conditioning in it also be classified as a semi-heated building?

No, the presence of air-conditioning would deem the building to be a conditioned space even if the heating system qualifies as a semi-heated space.

Does my warehouse/shop area need to meet the same requirements as my office area?

No, not necessarily, since each usage space may be considered differently. For example, while the office area may be defined as a conditioned space, the warehouse might qualify as a semi-heated space if there is no air conditioning, and the heating system is less than the lower limit for a conditioned space but more than the limit for an unconditioned space. See ASHRAE 90.1-2019 Table 3.2 Heated Space Criteria.

My COMcheck™ run keeps saying my design “Fails,” what is the best place to focus my attention to achieve compliance?

Look on the right-hand side of the “Envelope Assemblies” table of the COMcheck™ report and look for those items where the “Proposed U-Factor” is significantly higher than the “Budget U-Factor.” The items with the largest difference are the best places to focus on changes in the building envelope energy conservation system. Another possibility is to consider insulating the slab-on-grade floor if not already done.

CONCLUSION

Metal building systems have evolved notably in the past few decades and can readily meet high thermal performance standards. This is particularly true with the variety of energy conservation strategies available for the building envelope in metal roof and wall systems. The best, easiest, and most accurate way to demonstrate this for purposes of energy code compliance is by using COMcheck™ software. It has readily available information directly related to metal building systems based on ASHRAE approved assemblies that are recognized by the IECC. It also provides insight into how to adjust and improve performance in different parts of the building. The Metal Building Manufacturer’s Association, a not-for-profit organization, offers additional resources available at https://www.mbma.com.

Peter J. Arsenault, FAIA, NCARB, LEED AP is a nationally known architect and a prolific author advancing positive acoustical experiences through better building design. www.pjaarch.com, www.linkedin.com/in/pjaarch