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.