Frequently Asked Questions (FAQs)

• Copies of the International Energy Conservation Code (IECC) can be purchased from the International Code Council website.
• Copies of ASHRAE standards can be purchased from the ASHRAE website.
• For codes specific to a state or municipality, contact the authority having jurisdiction.

Both the 2009 and 2012 IECC require duct tightness to be verified. Verification can take place via either a post-construction test or a rough-in test.

For the post-construction test, leakage measurement must be made across the entire system, including the manufacturer’s air handler enclosure, with all register boots taped or sealed at a test pressure of 0.1 inches w.g. (25 Pa). The 2009 IECC limits the leakage to outdoors to less than or equal to 8 cfm per 100 ft² of conditioned floor area or total leakage less than or equal to 12 cfm per 100 ft² of conditioned floor area. The 2012 IECC only contains a requirement for total leakage of less than or equal to 4 cfm per 100 ft² of conditioned floor area.

For the rough-in test, leakage measurement is made across the system, with the manufacturer’s air handler enclosure if it is installed. The test is conducted at 0.1 inches w.g. (25 Pa) with all registers taped or sealed. The 2009 IECC limits leakage to less than or equal to 6 cfm per 100 ft² of conditioned floor area when the air handler is installed and 4 cfm when it is not installed. The 2012 IECC limits the leakage to 4 cfm per 100 ft² of conditioned floor area when the air handler is installed and 3 cfm when it is not installed.

After selecting a basement wall type, a basement wall illustration will appear with input boxes for the basement wall height, depth below grade, and depth of insulation. The illustration helps identify the dimensions being requested. You may enter basement wall dimensions directly into this illustration and select the OK button to have them transferred to the corresponding row in the table on the Envelope screen. If you prefer to enter the dimensions directly into the table on the Envelope screen, you can select Cancel to remove the illustration without entering dimensions. To view the basement wall illustration and inputs at a later time, click the right-mouse button anywhere on the basement row and select Edit Basement Inputs from the popup menu. 

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.

Walls that do not fit into any of the preset categories in REScheck (preset categories come directly from the applicable code currently selected in the Code menu) may be entered under the "Other" wall type. When "Other" is chosen as the wall type, the software requires an overall U-factor for the assembly. The assembly U-factor is calculated from the spacing of any framing and its R-value, the R-value of installed insulation, and the R-value of the balance of assembly (items such as OSB sheathing, drywall, interior and exterior air films, etc.). Details of how to perform a U-factor calculation can be found in any basic heat transfer text book or handbook.

The 2009 IECC requires that a minimum of 50% of the lamps in permanently installed lighting fixtures be high-efficacy lamps (2009 IECC, Section 404.1). The 2012 IECC has increased the minimum percentage from 50% to 75%, along with an exception for low-voltage lighting (2012 IECC, Section R404.1).

REScheck currently does not have a lighting input function; therefore, the lighting requirement should be confirmed under the Requirements Tab in the program.

REScheck 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. REScheck will perform trade-offs between envelope assemblies when determining compliance.

REScheck determines compliance for alterations in a similar manner as additions and new construction, however, each component that is being altered will need to be identified as either meeting an “exemption” from the drop down list of exemption choices or choose “no exemptions” apply and the proposed insulation and/or fenestration values must be entered.  REScheck will perform trade-offs between envelope assemblies that have been identified as “no exemptions” apply to the assembly when determining overall compliance for alterations for a specific project.

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.

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.

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.

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.

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.

The COMcheck trade-off alternative used for enforcing the IECC is permitted under a clause in Section 101 (referencing 2012 IECC). That clause is a fairly common code element that gives the jurisdiction and, more explicitly, the building official the latitude to allow any compliance approach that "makes sense" with respect to accomplishing the code's objectives. This kind of clause is often referred to as a "deemed to comply" approach. Through legislative and/or legal procedures, jurisdictions agree and accept to adopt this provision when adopting the IECC editions and in many cases amend the adopted code to explicitly include language that expressly permits use of the COMcheck software.

Specifically, Section 101 allows a building official to approve compliance tools that are deemed to meet "the intent of [the] code." The intent of the IECC commercial code is explicitly defined here: "C101.3 Intent. This code shall regulate the design and construction of buildings for the effective use and conservation of energy over the useful life of each building. This code is intended to provide flexibility to permit the use of innovative approaches and techniques to achieve this objective." The various compliance paths of the code are alternative "recipes" designed to achieve that intent, but Section 101 implies that other recipes are permitted if they accomplish the same overall objective.

The trade-off methodology used by COMcheck is consistent with the "Normative Appendix C: Methodology for Building Envelope Trade-Off Option" found in the referenced ASHRAE 90.1 code. However, to determine compliance with an IECC edition, all IECC requirements are applied to and enforced within that trade-off methodology including Section C402.3.1 "maximum fenestration and skylight area" (COMcheck restricts users from using the trade-off approach when the C402.3.1 provisions are not met, redirecting them to use of the referenced 90.1 as allowed by C401.2).

The IECC explicitly references what version of ASHRAE 90.1 corresponds with IECC sections on page C-78 of the 2012 IECC.

Codes: 2009 and 2012 IECC, ASHRAE Standard 90.1-13/2015 IECC

The 2009/2012 editions of the IECC (commercial provisions) do not include language explicitly describing a defined envelope trade-off compliance method. Only a set of prescriptive envelope requirements are provided. However, Section 101 of the IECC has a clause that has been widely interpreted and understood to give a building code official or jurisdiction the latitude to allow any compliance approach that "makes sense" with respect to accomplishing the code's objectives. This kind of clause is often referred to as a "deemed to comply" approach. Through legislative and/or legal procedures, jurisdictions agree and accept to adopt this provision when adopting the IECC codes.

Specifically, Section 101 allows a building official to approve compliance tools that are deemed to meet "the intent of [the] code." The intent of the IECC commercial code is explicitly defined here: "C101.3 Intent. This code shall regulate the design and construction of buildings for the effective use and conservation of energy over the useful life of each building. This code is intended to provide flexibility to permit the use of innovative approaches and techniques to achieve this objective." The various compliance paths of the code are alternative "recipes" designed to achieve that intent, but Section 101 implies that other recipes are permitted if they accomplish the same overall objective.

Excepting COMcheck support for 90.1-2013 and 2015 IECC, the envelope trade-off methodology used by COMcheck is the "Normative Appendix C: Methodology for Building Envelope Trade-Off Option" found in the referenced ASHRAE 90.1 code. The ASHRAE Appendix C trade-off method does include a limited number of “embedded” references to ASHRAE 90.1 based “prescriptive” requirements that must be enforced. Obviously, these prescriptive requirements are specific to ASHRAE 90.1 section numbers and thus relevant to the IECC codes. For this reason, and that it is only the “trade-off method” that is being “borrowed” for use with the IECC requirements, these Appendix C embedded requirements are not considered when this method is applied to the IECC codes in COMcheck. When applied to the IECC energy codes, all IECC code requirements are applied and enforced within that trade-off methodology when a clear and obvious reference can be established. More specifically, this applies to the table references to individual envelope assemblies U-factor requirements. 

The “embedded” Appendix C requirements discussed in the previous paragraph pertain to maximum window (WWR) and skylight (SRR) areas and minimum skylight area. When determining compliance to one of the ASHRAE 90.1 energy codes, COMcheck will enforce the WWR and SRR per guidance from Appendix C. However, the minimum skylight area requirement as described in Appendix C is worded and interpreted in such a way as to be deemed not applicable therefore is not enforced in COMcheck for either 90.1 or IECC energy codes. When determining compliance to one of the IECC codes the minimum skylight requirement will be enforced through the envelope report inspection checklist and the WWR and SRR requirements will be enforced prescriptively. That is, when complying with IECC and the WWR and SRR values are found to be noncompliant the user will be directed to use the equivalent ASHRAE 90.1 energy code.

To summarize, when the Appendix C trade-off method is applied to IECC codes, the IECC requirements will be applied to the method when and where that method provides guidelines for doing so. When guidelines are not provided by the trade-off method language or refers to nonexistent section numbers, the IECC requirement will be enforced prescriptively. As noted above, ASHRAE 90.1-2013 and 2015 IECC energy codes are exceptions to all of this discussion. ASHRAE 90.1-2013 Appendix C supports a trade-off method that is based on building performance simulations using EnergyPlus completely differently than earlier versions of the 90.1 code family. Only 90.1-2013 uses this method currently although 2015 IECC does allow a project to apply 90.1-2013 in its entirety as an alternative. 2015 IECC Component Performance Alternative is used for 2015 IECC and state codes based upon this code. This new compliance method replaces the use of ASHRAE 90.1 Appendix C and is based generally speaking on a “Total UA” approach.

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. 

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 5.5.4.2.1 and 5.5.4.4.1, 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.

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.

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)

or

(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.

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 5.1.2.3. 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 5.1.2.4. 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

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

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. 

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.

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.

In COMcheck 4.0.0.3 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.

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.

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 U_o‑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.