Frequently Asked Questions (FAQs)

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.

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. 

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

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. 

How do I enter fenestration that does not have a NFRC Product ID?

When entering your fenestration in COMcheck the pop up window has three options to enter your fenestration.  Choose the second option called Product Performance in accordance with NFRC.  If you do not have a pending product number, enter NA and enter your proposed values.  Note, test results should be submitted with the COMcheck report to verify the values entered.

 If the product has not been tested or accredited, choose option 3.  The code defaults come directly from the tables within the code.  Code defaults use worst case scenario for fenestration values and most defaults do not meet the prescriptive requirements dependent upon climate zone. Best recommendation is to choose fenestration products that are tested and NFRC labeled that have better U-factor and SHGC ratings.  

How does COMcheck calculate compliance for the building envelope?

COMcheck computes an envelope index that is a reflection of the difference between a 'design' building energy performance factor (EPF) and a 'code' or budget building EPF.  The total building load (made up of cooling, heating, lighting, and miscellaneous plug load) is determined by the location you are in, the specific assembly and building types you specify, and internal gains from lighting and miscellaneous plug loads, and of course the thermal properties and orientation of the envelope assemblies. The methodology used to determine EPF is provided in ASHRAE 90.1 Normative Appendix C: Methodology for Building Envelope Trade-off Option.

What is considered a commercial building?

A commercial building is defined as all other buildings that are not considered a residential building.

How does COMcheck show compliance for additions or alterations?

COMcheck determines compliance for additions in the same manner as new construction. When entering an addition, only the new portions of the building need to be shown in the software. COMcheck will perform trade-offs between envelope assemblies when determining compliance.

COMcheck determines compliance for alterations on a component-by-component basis. Each component is checked to verify it meets or exceeds the minimum prescriptive requirements of the selected code. No trade-offs are available for alterations and no compliance percentage will be generated–the software shows a pass/fail for compliance.

How are lighting exemptions and allowances shown in COMcheck?

Exemptions and allowances for lighting are an option that must be activated in COMcheck. To activate the exemptions and allowances, take the following steps:

  • Select either the Interior Lighting or Exterior Lighting Tab
  • Go to the Options menu and select Interior Lighting Exemptions and Allowances for Interior Lighting or Exterior Lighting Exemptions for Exterior Lighting.

Note that activation of the exemptions and allowances will add an extra column to the applicable worksheet–it may be necessary to enlarge the window in order to see the new column.

Can compliance be shown for only one area in COMcheck (Envelope, Lighting, or Mechanical)?

If multiple users are putting information into COMcheck, each may fill out the appropriate section independently. However, all sections of the building must show compliance to the same code or standard (e.g., cannot show envelope compliance to IECC and lighting compliance to ASHRAE Standard 90.1). COMcheck does not require that all sections be completed to perform compliance checks.

How do mixed use buildings need to meet code?

The IECC addresses mixed occupancies by stating that commercial occupancies must comply with the commercial portion of the code and residential occupancies must comply with the residential portion of the code.  

ASHRAE Standard 90.1 addresses high-rise residential and all other commercial buildings.  Residential spaces are those used primarily for living and sleeping and include dwelling units, hotel/motel guest rooms, dormitories, nursing homes, patient rooms in hospitals, lodging houses, fraternity/sorority houses, hostels, prisons, and fire stations.

To what code must compliance be shown?

Code adoption takes place at the state, and in some cases municipal, level. To determine the code in a particular state, visit the Status of State Energy Code Adoption page.

How are spandrel or translucent wall systems input in COMcheck?

Fenestration is considered anything that transmits light, however, COMcheck cannot calculate fenestration without having a wall associated with it. In this case the wall is entirely fenestration therefore, the square footage would be the same for both the wall and window area and the software will calculate the wall area as net zero since the fenestration is the entire wall.

For the spandrel glass or translucent wall systems the way to enter that into COMcheck would be to first define a wall by choosing wall as "other" from the drop down list of wall assembly types, enter the square footage of the wall system (e.g. 100 sq. ft), enter the U-factor for the wall system (e.g. 0.23) and also you will need to enter the heat capacity of the wall. For information on heat capacity and how to calculate it, in COMcheck, go to the help menu, help topics and wall software inputs.

After defining the wall, define the window area by choosing window as "other" from the drop down list of window assembly types, enter the square footage of the wall system (e.g. 100 sq. ft.) and choose option two under Fenestration details "Product performance tested in accordance with NFRC", if you do not have a product ID, enter "NA", then enter your U-factor and SHGC values from the product manufacture specifications.

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.