International Code Requirements for Residential Windows and Doors 2016: Energy Performance

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Requirements for energy performance in both residential and commercial buildings are spelled out in the 2015 IECC. The energy conservation requirements for one- and two-family homes and townhouses three stories or less in height are also given in Chapter 11 of the 2015 IRC.

Beginning with the 2012 International Codes, the energy conservation provisions of Chapter 11 of the IRC are an exact duplicate of the provisions of the IECC for the same building. Previously, there was some variation in the energy performance requirements for residential buildings that were included in both the IECC and the IRC. In jurisdictions using the 2009 or earlier editions of these two codes, it is essential to verify which set of requirements are to be complied with for residential construction before beginning a project.

The residential provisions of the 2015 IECC apply to one- and two-family homes and other types of residential construction— such as multifamily buildings and assisted-living facilities—that are three stories or less in height. For these buildings, the residential provisions of the 2015 IECC govern if it has been adopted by the Authority Having Jurisdiction. (Other types of residential occupancies, such as multifamily buildings and assisted-living facilities greater than three stories in height, and hotels and motels of any height, are governed by the provisions of the 2015 IECC for commercial buildings.)

Compliance Paths

The most significant change in the residential provisions of the 2015 IECC has been the addition of a new compliance path, making a total of four for residential construction:

1. The prescriptive path,
2. The UA alternate method,
3. The whole building performance path, and
4. The Energy Rating Index path.

The prescriptive path is the simplest to use. It provides one set of energy efficiency requirements for each component of the building envelope.

Under the prescriptive path of the 2015 IECC for residential construction, there is no limit on the percentage of glazing in the exterior wall. There is also no limit on the percentage of roof area containing skylights.

The prescriptive path for residential construction establishes maximum permitted U-factor and solar heat gain coefficient requirements for fenestration. These values did not change between the 2012 and the 2015 editions of the IECC.

U-factor is to be determined in accordance with National Fenestration Rating Council 100-09 or by use of a default table in the 2015 IECC. Similarly, the SHGC of the fenestration is to be determined in accordance with NFRC 200-09 or by use of a default table. Figures 1 and 2 show the maximum permitted U-factor and SHGC for vertical fenestration and skylights in low-rise residential construction when the prescriptive path of the 2015 IECC and 2015 IRC is used.

The other three compliance paths for residential construction in the 2015 IECC permit some tradeoffs in levels of energy efficiency from one building component to another. One of these—designated the UA alternate method—only permits tradeoffs between different elements of the building envelope.

The whole building performance path permits tradeoffs between some components of the residence that impact energy use. The ability to trade off a more efficient mechanical system for other components of the building, however, is not included in the list of those permitted in the 2015 IECC. This change from previous editions removed a significant incentive for builders to install more efficient mechanical systems than what is currently required by federal law.

Beyond this, the amount of tradeoff that is permitted for fenestration when following the UA alternate method or whole building performance paths also continues to be capped in the 2015 IECC. The performance caps are as follows:

  • In the Northern climate zones 6 to 8 (roughly corresponding with Wisconsin to Alaska), the U-factor is not to exceed 0.40.
  • In mid-level climates zones 4 and 5 (Northern Tennessee to Southern Wisconsin), the U-factor is not to exceed 0.48.
  • In Southern climate zones 1 to 3 (Tennessee on south to the tip of Florida), there is no U-factor cap, but the SHGC is not to exceed 0.50.
  • The U-factor of skylights in climate zones 4 to 8 is not to exceed 0.75. The same SHGC cap of 0.50 that applies to vertical fenestration in climate zones 1 to 3 also applies to skylights.

Exterior Glass Doors

The U-factor requirements discussed above for vertical fenestration also apply to exterior glass doors. Glass doors, by definition in the IECC, are considered to be those which are more than 50 percent glass in area. If the door is equal to or less than 50 percent glass, it is considered to be an opaque door. Although opaque doors are included in the definition of fenestration area in the 2015 IECC and 2015 IRC, they are assigned a maximum U-factor of 0.35, separate from the U-factor requirements for vertical fenestration.

According to Table R303.1.3(2) of the 2015 IECC, this criterion is considered to be met by any insulated, nonmetal edge opaque door with glazing less than 45 percent of the door area, when any glazing that does occur in the door is double pane. Also, one opaque door up to 24 square feet in area is exempt from the maximum U-factor requirement in the 2015 IECC and 2015 IRC.

The New ERI Path

The new Energy Rating Index path in the 2015 IECC compares the anticipated energy usage of the proposed residence to that of one built under the 2006 IECC. The 2015 IECC requires residences built using this compliance path to not consume more than 51 to 54 percent of the energy used for a similar size home built under the 2006 IECC, based upon location of the residence.

Although similar in concept to the whole-building performance path, there are a few key differences. Specifically:

  • Use of the Energy Rating Index compliance path requires third-party verification of compliance.
  • Although some trade off of U-factor and SHGC is permitted when using the ERI compliance path, both are limited to no greater than that permitted for the prescriptive path in the 2009 IECC. As a general rule, these caps are more stringent than the maximum U-factor and SHGC permitted when the whole building performance path or UA alternate method of the 2015 IRC are used.

Air Leakage

The 2015 IECC and IRC require air leakage resistance of windows, door assemblies and unit skylights to be determined in accordance with NAFS-11 or NFRC 400-09. This is similar to the requirements in the 2012 IECC and IRC.

The pass/fail criterion for windows, skylights and sliding glass doors is 0.3 cfm per square foot. The pass/fail criterion for swinging doors is 0.5 cfm per square foot.

See also

Main Article

Design Loads