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High-R Windows

Select high-performance windows that meet or exceed code and energy-efficiency program requirements. High-efficiency windows typically consist of two or more panes of glass in a fiberglass, vinyl, wood, or combination insulated frame, with low-emissivity (low-e) coatings on the glass panes and a nontoxic inert gas like argon filling the space between the panes to provide better insulation than plain air. Windows are typically the weakest performing component of the wall from a thermal insulation perspective. Windows typically have insulation values of R-1 for single-pane aluminum-framed windows to R-6 for the highest-performing triple-pane windows. In comparison, insulated walls typically have R-values of R-13 to R-25 or higher. Therefore, selecting and properly installing high-performance windows during initial construction can be a cost-effective measure over the life of the home.  For more information about the features of high-performance windows, see the guide ENERGY STAR Windows.

DOE Zero Energy Ready Home Program Notes

The U.S. Department of Energy Zero Energy Ready Home Program allows builders to choose either a prescriptive path or a performance path in order to certify their homes as DOE Zero Energy Ready Homes.

DOE’s Zero Energy Ready Home’s National Program Requirements specify as a mandatory requirement (Exhibit 1, #2.1) that all labeled homes shall meet or exceed the latest ENERGY STAR Program Requirements for Residential Windows, Doors, and Skylights in effect at the time of project permitting. The latest version of the ENERGY STAR Residential Windows, Doors, and Skylights  specification (Version 6) became effective January 1, 2015, for climate zones 1-4 and January 1, 2016, for climate zones 5-8 and marine 4. The ENERGY STAR window requirements are shown in Table 1. Although DOE's Zero Energy Ready Home Program requires builders to meet the ENERGY STAR windows criteria, DOE has determined to phase in the updated windows specifications so builders in the northern climates will be required to meet the new specifications for homes permitted after August 31, 2016.

Table 1. ENERGY STAR Windows Criteria, Version 6

windows2

In Exhibit 2 of the Zero Energy Ready Home National Program Requirements (excerpt shown in Table 2 below), DOE specifies more stringent fenestration (window) criteria. Builders using the Zero Energy Ready Home prescriptive path must meet or exceed these criteria. Builders using the Zero Energy Ready Home performance path must use these criteria when modeling the target home.

Table 2. Fenestration Requirements Excerpted from Exhibit 2 of the DOE Zero Energy Ready Home National Program Requirements

DOE Zero Energy Ready Home National Program Requirements Footnotes:

(7) State energy code specifications that exceed the DOE Zero Energy Ready Home National Program Requirements always take precedence and shall be used instead of DOE Zero Energy Ready Home specifications to determine DOE Zero Energy Ready Home compliance.

(12) Windows shall meet the applicable ENERGY STAR Window Product Criteria based on the following schedule:

  • For projects permitted on or before 8/31/2015, windows shall meet ENERGY STAR Windows Eligibility Criteria Version 5.0
  • For projects permitted after 8/31/2015, windows shall meet ENERGY STAR Windows Eligibility Criteria Version 6.0; except for Climate Zones 5 through 8 and Zone 4 Marine, which must follow ENERGY STAR Windows Eligibility Criteria Version 6.0 for projects permitted after 8/31/2016

See www.energystar.gov/windows for current ENERGY STAR Windows Eligibility Criteria. For homes achieving PHIUS+ certification where triple glazed window assemblies with thermal breaks/spacers between the panes are used, such windows are deemed to meet this requirement even in the absence of an ENERGY STAR certification.

(13) Fenestration shall meet the applicable ENERGY STAR Windows Eligibility Criteria for U and SHGC, with the following exceptions:

a. An area-weighted average of fenestration products shall be permitted to satisfy the U-factor requirements;

b. An area-weighted average of fenestration products ≥ 50% glazed shall be permitted to satisfy the SHGC requirements;

c. 15 square feet of glazed fenestration per dwelling unit shall be exempt from the U-factor and SHGC requirements, and shall be excluded from area-weighted averages calculated using a) and b), above;

d. One side-hinged opaque door assembly up to 24 square feet in area shall be exempt from the U-factor requirements and shall be excluded from area-weighted averages calculated using a) and b), above;

e. Fenestration utilized as part of a passive solar design shall be exempt from the U-factor and SHGC requirements, and shall be excluded from area-weighted averages calculated using a) and b), above. Exempt windows shall be facing within 45 degrees of true South and directly coupled to thermal storage mass that has a heat capacity > 20 btu / ft3x◦F and provided in a ratio of at least 3 sq. ft. per sq. ft. of South facing fenestration. Generally, thermal mass materials will be at least 2 in. thick.

(15) In states where the residential provisions of the 2012 International Energy Conservation Code (IECC) have been adopted, qualifying homes must instead meet the envelope insulation requirements of the 2015 IECC, effective 12  months after the effective date of the 2012 IECC in that state. The exact date at which time a state will migrate to 2015 IECC envelope compliances may vary based on the timing of RESNET rating software updates, but will not be any sooner than 12 months following the effective dateof teh 2012 IECC in that state.  

(25) All decorative glass and skylight window areas count toward the total window area to above-grade conditioned floor area (WFA) ratio.

(26) DOE strongly encourages all DOE Zero Energy Ready Home partners to consider using R-5 windows in cold climates in anticipation of them becoming the state-of-the-art window choice in the near future. Visit the DOE web site for more details and sources of these windows.

(27) For homes using Exhibit 2 for Prescriptive compliance with the DOE Zero Energy Ready Home, the exceptions listed in Footnote 13 above apply to the U-Value and SHGC requirements in Exhibit 2.

(28) For Prescriptive Path: All decorative glass and skylight window areas count toward the total window area to above-grade conditioned floor area (WFA) ratio. For homes using the Prescriptive Path that have a WFA ratio > 15%, the following additional requirements apply:

a.  In Climate Zones 1, 2, and 3, an improved window SHGC is required and is determined by:
Improved SHGC = [0.15 / WFA] x [ENERGY STAR SHGC]
Where the ENERGY STAR SHGC is the maximum allowable SHGC in Exhibit 1, ENERGY STAR Reference Design, for the Climate Zone where the home will be built.

b.  In Climate Zones 4, 5, 6, 7, and 8, an improved window U-Value is required and is determined by:
Improved U-Value = [0.15 / WFA] x [ENERGY STAR U-Value]
Where the ENERGY STAR U-Value is the maximum allowable U-Value in Exhibit 1, ENERGY STAR Reference Design, for the Climate Zone where the home will be built.

ENERGY STAR Certified Homes Notes

ENERGY STAR Certified Homes (Ver. 3/3.1, Rev 08) windows criteria are provided in the Building America Solution Center guide ENERGY STAR Windows.

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Last Updated: Wednesday, July 6, 2016