Frequently Asked Questions (FAQs)

Can I share my saved lighting fixture library on another computer?


  1. Locate the lighting fixture library in this location defaulted by COMcheck:   
    C:\Users\<your user name>\AppData\Roaming\COMcheck\fixtureLibrary.xml.
  2. Copy fixtureLibrary.xml from this location to the same directory on the other computer.
Are projects required to be completed by a registered design professional?

The commercial energy code requires that a registered professional submit compliance documentation (construction documents and compliance verification).    In the IECC, Section C103.1 Construction Documents, General, the wording states that construction documentation and other supporting data shall be submitted in one or more sets with each application for a permit.  The construction documents shall be prepared by a registered design professional where required by the statutes of the jurisdiction in which the project is to be constructed.  Where special conditions exist, the code official is authorized to require necessary construction documents to be prepared by a registered design professional.

The definition in the code for a registered design professional is:  an individual who is registered or licensed to practice their respective design profession as defined by the statutory requirements of the professional registration laws of the state or jurisdiction in which the project is to be constructed.

As for COMcheck, there are no requirements as to who can use it and who can create a compliance report, but as to who signs and submits the report, the requirements stated above should be followed.

Can you combine two data files into one project?

Unfortunately, there is not a way to merge files.  The web tool is definitely the way to go when you have multiple contractors involved as you can create a generic log in and each contractor can work on the same project file to enter their information (e.g., building envelope, lighting, mechanical). 

Project sharing will soon be more user friendly. 

Do electric central furnaces qualify for the High Performance HVAC Efficiency package in the 2012 IECC?

Electric central furnace does not qualify for the High Performance HVAC efficiency package. ALL systems in a project must meet the criteria of C406.2 and if your system(s) cannot be found in C406.2 then by default it does not qualify. In these cases if you want to use the electric central furnace then you have to choose a different additional efficiency package.

The following is the code section that enforces this:

C406.2 Efficient HVAC performance. Equipment shall meet the minimum efficiency requirements of Tables C406.2.(1) through C406.2(7) in addition to the requirements in Section C403. This section shall only be used where the equipment efficiencies in Tables C406.2(1) through C406.2(7) are greater than the equipment efficiencies listed in Table C403.2.3(1) through 403.2.3(7) for the equipment type.

When entering doors in COMcheck, do I use "operable U-factor" or "caclulated U-factor?"

“Standard 90.1 requires that U-factors (and air leakage) for doors be determined in accordance with the NFRC rating procedures.  All NFRC ratings are based on the whole product, including the frame.”

Consequently, for compliance with Standard 90.1, door U-factors must be:

  • either determined in accordance with NFRC 100 or
  • assigned the default values in Section A7.1.

Both the NFRC 100 and the Section A7.1 values are for the overall door area, including the door slab and the door frame.

In the same way that some window manufacturers only refer to the center of glass performance (and to ignore the thermal bridging through the window frame), door manufacturers have preferred to talk about the door slab only (and to ignore the thermal bridging in the frame).  However, Standard 90.1 requires whole product ratings in accordance with NFRC 100.  

The bottom line from a strict 90.1 and IECC perspective is that if the U-factor is not developed using NFRC 100, the default values in Standard 90.1 must be used.  These defaults are available in COMcheck and can be used.  They represent very poorly performing doors, which can be an issue for some buildings if the door area is a significant fraction of the wall area.

Why do I get an error when I click on "Check Compliance?"

When clicking “check compliance” the program displays an error message that “REScheck could not complete performance alternative calculations.  Review input and edit as necessary.” 

The problem most likely relates to the basement walls you have specified. The DOE-2 simulation program used in REScheck for performance alternative calculations sometimes generates this error even though the entries appear valid.

As a workaround, we recommend that you split your basement walls so that for each basement wall you add a new above-grade wall to represent the above-grade area of the basement wall. 

Why won't the report print?

The file is saved but I cannot get a pdf or rtf file to print.

There are a couple of things to try:

  1. Completely remove REScheck or COMcheck

    • Use the Windows operating system “Programs and Features” uninstaller
    • Open Windows Explorer and navigate to C:\Users\<your username>\AppData\Roaming\<REScheck or COMcheck>
    • Delete the check.prp and defaults.dat files
    • Navigate to the REScheck or COMcheck application folder:  C:\Users\<your username>\AppData\Local\Check\<REScheck or COMcheck>
    • Delete all of the contents of this folder, including any sub-folders
      (These steps should ensure the application has been fully removed.)
    • Then try reinstalling REScheck or COMcheck
  2. If that doesn’t work, use the web tool which requires no download but you will want to register so you can save your projects.   
How does the importing of a gbxml file option function?

There are a couple things to note about the current import process implementation:

  • Currently we only focus on importing envelope components. This means you will still be required to manually specify your space types, lighting fixtures, and mechanical systems that appear in your building.
  • Depending on the size of your building, a gbXML file can potentially contain thousands of surfaces to fully represent your structure. Working with that many envelope components in COMcheck is unreasonable, which is why we identify surfaces with similar characteristics and aggregate them during the import process.
Is thermal bridging taken into account and any other parts of a wall assembly such as the girts, z clips, framing members, etc.?

COMcheck does account for thermal bridging of framing members, furring, etc. (depending upon the assembly). U-factor assembly calculations are taken from ASHRAE Appendix A and ASHRAE Fundamentals. The methodology used to calculate compliance is taken from ASHRAE Appendix C. When an assembly is chosen from the drop down lists in the program, there is a U-factor automatically displayed for that assembly (excluding fenestration). Once the user enters the proposed insulation R-value(s) for the assembly, the program recalculates the assembly and updates the U-factor to the overall U-factor for the entire assembly. Also users have the option to choose "other" as the assembly type. If “other” is selected, the user will then need to enter the overall calculated U-factor for the entire assembly and document those calculations to the building official.

What do I use if my city is not listed?

Choose a city that is the closest with the most similar weather.  Check with the building official where the project is located to confirm the city selected will be acceptable or if choosing “county” as the designation would be more appropriate.  The easiest way to choose county would be to use the web tool which has the option between city and county on the project tab screen.

How are louvers identified in COMcheck?

Louvers are best treated as un-insulated portions of the wall. You can add them as a separate wall type (for example, if they are metal, metal building would probably be most appropriate) with no insulation but a wall area. COMcheck will do the area-weighted averaging for the opaque wall to calculate the overall U of the opaque wall. The impact of having an uninsulated wall area is that you will be required to “make up for that” in some other portion of the building envelope. This may mean more insulation on the rest of the wall, better windows, or more roof insulation.

Note:  There is an allowance for up to 1% of wall area in “recessed equipment” in walls in Standard 90.1 if 90.1 is the code in which you are complying with. 

Does REScheck account for compression of insulation in a wall assembly?

REScheck uses nominal insulation R-values. The program does not calculate for compression. For example, if R-19 is entered as the cavity insulation R-value, it assumes the full R-19 in REScheck. Walls with insulation R-values equal to or less than R-15 are modeled in REScheck as having 2x4 studs at either 16” or 24” O.C. (on center) and cavity wall insulation R-values greater than R-15 are modeled as 2x6 studs at either 16” or 24” O.C. For more detailed information on how the walls are calculated please refer to the Methodology/Technical Support document.

What is considered a residential building?

The term “residential building” includes:

  1. detached one-or-two family dwellings having not more than three stories above grade plane;
  2. buildings that consist of three or more attached townhouse units and have not more than three stories above grade plane;
  3. buildings that are classified in Group R-2, R-3 or R-4 and have not more than three stories above grade plane
How is Cavity and Continuous Wall Insulation Calculated in REScheck?

Exterior walls in REScheck are defined by the assembly type, gross wall area, cavity/continuous R‑value (U-factor for Other walls) and orientation.  All exterior walls are assumed to be of regular rectangular shape with an average wall height of 9 ft., and the wall width is calculated from the gross area as input by the user. 

REScheck wall materials are assumed to be plywood siding, plywood structural sheathing, and foam insulation sheathing on the framing exterior, batt insulation, wood framing, and 1/2-in. gypboard on the interior.  The entire wall is assumed to have structural sheathing. When continuous foam insulation is specified, 100% of the wall is assumed to be covered at the specified R-value.

The Uo‑factor for all frame walls is based on the R‑value of cavity insulation and the continuous insulation R‑value (if used).  If the user does not enter a continuous insulation (sheathing) R‑value (or enters a value of 0.0), the software assumes a sheathing R‑value of 0.83.  This default value gives credit for some minimal type of sheathing material (such as plywood) under the siding. 

Continuous Insulation

Insulation that runs continuously over structural members and is free of significant thermal bridging; such as rigid foam insulation above the ceiling deck. It is installed on the interior, exterior, or is integral to any opaque surface of the building envelope.

Cavity Insulation

Insulation installed between structural members such as wood studs, metal framing, and Z-clips.

Cavity insulation is used within the wood- or metal-framed wall, while rigid continuous insulation (c.i.) is placed on the exterior side of the framing.  Alternative combinations of cavity insulation and sheathings in thicker walls can be used, provided the total wall assembly has a U-factor that is less than or equal to the appropriate climate zone construction requirements.

Cavity Insulation Calculation in REScheck

REScheck uses nominal insulation R-values. The program does not calculate for compression. For example, if R-19 is entered as the cavity insulation R-value, it assumes the full R-19 in REScheck. Walls with insulation R-values equal to or less than R-15 are modeled in REScheck as having 2x4 studs at either 16" or 24" O.C. (on center) and cavity wall insulation R-values greater than R-15 are modeled as 2x6 studs at either 16" or 24" O.C. 

Continuous Insulation Calculation/Insulated Sheathing

The assemblies listed in REScheck already have a default value added for standard sheathing (depending on the assembly component). If no sheathing is indicated by the user, the sheathing is assumed to be plywood with an R-value of 0.83. If insulated sheathing is used, only 80% of the net wall is assumed to be covered by the insulated sheathing. The other 20% is assumed to be covered with plywood.

REScheck Quick Tip

Cavity R-Value - Enter the R-value of any insulation to be installed in the cavities between above-grade wall structural members. The insulating values of other parts of the building assembly (e.g., gypsum board and air films) are accounted for by the program and should not be included.

REScheck  wall assemblies assume cavity insulation completely fills the cavity.  Users who have unique wall assemblies where the cavity is not completely filled with insulation must account for the air space within their wall assembly calculation and should use “other” as the wall type and enter their respective overall calculated U-factor.

Continuous R-Value - Enter the R-value of any continuous insulation in the above-grade wall. Continuous insulation is continuous over framing members or furring strips and is free of significant thermal bridging. The R-values of other parts of the building assembly (e.g., gypsum board and air films) are accounted for by the program and should not be entered. Insulated sheathing installed on the exterior of above-grade walls is an example of continuous insulation. For structural insulated panels and insulated concrete forms, enter the manufacturer-reported R-value for the entire assembly.

Does REScheck account for compression of insulation in a wall assembly

REScheck uses nominal insulation R-values. The program does not calculate for compression. For example, if R-19 is entered as the cavity insulation R-value, it assumes the full R-19 in REScheck. Walls with insulation R-values equal to or less than R-15 are modeled in REScheck as having 2x4 studs at either 16" or 24" O.C. (on center) and cavity wall insulation R-values greater than R-15 are modeled as 2x6 studs at either 16” or 24” O.C. 

For more detailed information on how the walls are calculated please refer to the REScheck Technical Support Document.

How do I enter VRF Systems into COMcheck?

In COMcheck and newer, you can now break up your VRF into two systems.  One can be defined as the VRF Outdoor/Central unit and is selected as heating equipment→heat pump list-→"VRF xxxx". This type of system will enforce the system efficiency depending on the system cooling capacity.

If the economizer requirement is enforced you can select the economizer exception "VRF Outdoor/Central Unit". The other VRF system you would specify is from the cooling equipment side of the HVAC systems dialog and is called "VRF Zone Fan Unit". If you select this as your system the capacity of individual units will generally be so small that the economizer requirement will not be enforced. And the system efficiency is also not enforced as there is no efficiency requirement for this part of the VRF system.

Notes: If you don't find the VRF system available in the HVAC system dialog then it is probably due to the energy code you have selected. Some energy codes don't enforce compliance with VRF systems. 2009 IECC and 90.1-2007 are 2 of them. If VRF isn't found in the energy code being used it is because it is not enforced by that energy code.

Were the provisions for air leakage changed in 2012 IECC compared to 2009 IECC?

Yes, in Section 402.4 of the 2012 IECC, testing is now required instead of an option between testing or visual inspection such as in the 2009 IECC.  Also, the air leakage rates changed.


Air Leakage Rates       2009 IECC        2012 IECC

Climate zones 1-2  

     <7 ACH @ 50 Pa  

     <5 ACH @ 50 Pa

Climate zones 3-8    

     <7 ACH @ 50 Pa

     <3 ACH @ 50 Pa

How can a COMcheck-Web or REScheck-Web project be shared with other team members?

To share a particular project with others on COMcheck-Web or REScheck-Web, you have a couple options:

  1. One option is to share the log in credentials with them and save all edits to the project under that account. If you are concerned about others having access to your personal account you can set up an independent account (using a unique email from your own present account) and create or upload the project to that new "shared" account.
  2. The other option is to take advantage of the Sharing feature in REScheck-Web (see the Getting Started document for details), or download a COMcheck-Web project from your personal account to your desktop then email or hand off the downloaded project file (e.g., myProjectFile.cxl) to other team members. The other team members would each have to upload that cxl file to their account. To do this:
    • Use the button to the right of the "Project Title" edit box (top center of screen) in the Web app. (The upload features requires you to be logged into your account.)
    • Once logged in, the Upload feature is available by clicking My Projects (upper right area of screen)
    • then at the bottom of the popup window click the "Upload project from my computer..." hyperlink
    • click on "Browse...". Navigate to the file on your PC and when selected click Upload.

    Note: if you have many projects already loaded in your account you might need to click All at the top of the My Projects window to see all the projects. Otherwise, only the more recently used projects are listed.


What is required for historic buildings?

Note:  The key point is not the age of the building, but whether it is registered or eligible to be registered and listed.  In the following cases, historic buildings are considered exempt from provisions of the energy code (however, we recommend always confirming with the state or local jurisdiction):

  • listed in the State or National Register of Historic Places;
  • designated as a historic property under local or state designation law or survey,
  • certified as a contributing resource with the National Register listed or locally designated historic district; or
  • with an opinion or certification that the property is eligible to be listed on the National or State Registers of Historic Places either individually or as a contributing building to a historic district by the State Historic Preservation Officer or the Keeper of the National Register of Historic Places. 
Does my building need to comply with the energy code if it will not be cooled or heated?

In the 2015 IECC, Section C402.1.1 Low-energy buildings – low energy buildings or portions separated from the remainder of the building by a building thermal envelope complying with the code, can be exempt from the building thermal envelope provisions of Section C402 if:

  1. Has a peak design rate of energy usage less than 3.4 Btu/h * ft2 or 1.0 watt/ft2 of floor area for space conditioning purposes
  2. Those that do not contain conditioned space
  3. Greenhouses
Does energy code compliance need to be shown for a warehouse?

Warehouses must be considered carefully. The first consideration is whether it is going to be conditioned, cooled and/or heated, or semi heated. Next is the applicable energy code. Older codes did not require the building envelope to meet the energy provisions if the warehouse didn't include mechanical equipment and was unconditioned. In ASHRAE 90.1-2010 and -2013, buildings being constructed must be assumed to be conditioned.

ASHRAE 90.1-2010/90.1-2013 Section Spaces shall be assumed to be conditioned spaces and shall comply with the requirements for conditioned spaces at the time of construction, regardless of whether mechanical or electrical equipment is included in the building permit application or installed at that time.

ASHRAE 90.1-2010/90.1-2013 In Climate Zones 3-8, a space may be designated as either semi-heated or unconditioned only if approved by the building official.

One of the reasons for this change, is years ago shell buildings being built did not have to meet the building envelope provisions, however, the intent of these buildings is that later on the spaces would be leased out and most likely conditioned.  The expense of bringing an existing building up to code can be very costly especially if portions have to be completely rebuilt to accommodate insulation. 

So, if you have a warehouse that is strictly just a warehouse (unconditioned), confirm with the code official as to whether the building envelope must meet the energy provisions even if you are complying to an older code

What are space conditioning types?

ASHRAE’s space conditioning types include: conditioned space, unconditioned or semi-heated space. ASHRAE’s definitions for these types:

space: an enclosed space within a building. The classifications of spaces are as follows for the purpose of determining building envelope requirements.

(a) conditioned space: a cooled space, heated space, or indirectly conditioned space defined as follows.

1. cooled space: an enclosed space within a building that is cooled by a cooling system whose sensible output capacity exceeds 5 Btu/h*ft2 of floor area.

2. heated space: an enclosed space within a building that is heated by a heating system whose output capacity relative to the floor area is greater than or equal to the criteria in Table 3.1.

3. indirectly conditioned space: an enclosed space within a building that is not a heated space or a cooled space, which is heated or cooled indirectly by being connected to adjacent space(s) provided:

(a) the product of the U-factor(s) and surface area(s) of the space adjacent to connected space(s) exceeds the combined sum of the product of the U-factor(s) and surface area(s) of the space adjoining the outdoors, unconditioned spaces, and to or from semi-heated spaces (e.g., corridors)


(b) that air from heated or cooled spaces is intentionally transferred (naturally or mechanically) into the space at a rate exceeding 3 air changes per hour (ACH) (e.g., atria).

(b) semiheated space: an enclosed space within a building that is heated by a heating system whose output capacity is greater than or equal to 3.4 Btu/h*ft2 of floor area but is not a  conditioned space.

(c) unconditioned space: an enclosed space within a building that is not a conditioned space or a semiheated space.

How does COMcheck calculate percentage of glazing?

COMcheck implements the calculation based on the definition of above and below-grade walls in the applicable code.  The calculation for percentage of glazing in ASHRAE Standard 90.1 and the IECC are different as the IECC only looks at above grade walls and 90.1 includes both above and below grade walls.

From ASHRAE 90.1-2010

5.5, Prescriptive Building Envelope Option, provided that 

  1. the vertical fenestration area does not exceed 40% of the gross wall area for each space-conditioning category

wall: that portion of the building envelope, including opaque area and fenestration, that is vertical or tilted at an angle of 60 degrees from horizontal or greater. This includes above- and below-grade walls, between floor spandrels, peripheral edges of floors, and foundation walls. For the purposes of determining building envelope requirements, the classifications are defined as follows:

above-grade wall: a wall that is not a below-grade wall.

below-grade wall: that portion of a wall in the building envelope that is entirely below the finish grade and in contact with the ground.

wall area, gross: the area of the wall measured on the exterior face from the top of the floor to the bottom of the roof.

From 2012 IECC:

C402.3.1 Maximum area. The vertical fenestration area (not including opaque doors and opaque spandrel panels) shall not exceed 30 percent of the gross above-grade wall area.

Can I show compliance using COMcheck if my glazing is over the 40% threshold in the 2009 IECC?

The Scope and Application sections of the 2009 IECC address use of ASHRAE 90.1 (2007) as an alternative.  See below for the text.  It is appropriate to use ASHRAE 90.1 as an alternative when your building exceeds 40% glazing, although it does not guarantee your building will comply.  ASHRAE offers an exception to the 40% limitation that calculates the partial shading provided by permanent opaque projections (Refer to ASHRAE 90.1-2007 Sections and, Exception (b)).

501.1 Scope.  The requirements contained in this chapter are applicable to commercial buildings, or portions of commercial buildings.  These commercial buildings shall meet either the requirements of ASHRAE/IESNA Standard 90.1, Energy Standard for Buildings Except for Low-Rise Residential Buildings, or the requirements contained in this chapter.

 501.2 Application.  The commercial building project shall comply with the requirements in Sections 502 (Building envelope requirements), 503 (Building mechanical systems), 504 (Service water heating) and 505 (Electrical power and lighting systems) in its entirety.  As an alternative the commercial building project shall comply with the requirements of ASHRAE/IESNA 90.1 in its entirety.  Exception:  Buildings conforming to Section 506, provided sections 502.4, 503.2, 504, 505.2, 505.3, 505.4, 505.6 and 505.7 are each satisfied.

Why am I receiving an error message that the check envelope compliance simulation failed?

When using the ASHRAE 90.1-2013 energy code, COMcheck needs to have two EnergyPlus weather files in this folder C:\ProgramData\COMcheck\eplus\weather. The most common reasons for a compliance simulation failure are: 

  1. the files are not located at this default location
  2. only one file is there instead of the two needed
  3. the files are of a different size than anticipated.

The two weather files will have names and file sizes similar to these (of course the file names will reflect your building’s project location):

  • USA_NJ_Newark.Intl.AP.725020_TMY3.epw (~1,619 KB)
  • USA_NJ_Newark.Intl.AP.725020_TMY3.ddy (~29 KB)

What to do if you get this error:  Delete one or both weather files and attempt to run simulations again so that the weather download process gets executed again.

How it works:  If these weather files are not found at the expected location (C:\ProgramData\COMcheck\eplus\weather), COMcheck will attempt to download them. 

NOTE:  Once these weather files are downloaded they will remain on the PC at C:\ProgramData\COMcheck\eplus\weather.  Therefore, the weather download process only needs to execute one time per unique project location. Obviously for this process to work the current user must have user privileges that permit COMcheck to establish an internet connection and to download these files.