Windows and Doors under LEED for Homes

A closer look at the USGBC program and what it says about fenestration products

Green Resource Center logoThe U.S. Green Building Council's LEED for Homes third-party certification system measures the overall performance of a home in eight categories—Innovation & Design Process, Location & Linkages, Sustainable Sites, Water Efficiency, Energy & Atmosphere, Materials & Resources, Indoor Environmental Quality and Awareness & Education. The program establishes a minimum level of performance through prerequisites in each category and rewards credits for higher performance. LEED homes receive one of four performance ratings—certified, silver, gold or platinum—according to the total credits earned.

ENERGY PERFORMANCE
Covering a broad array of issues related to the environmental impact of homes, steps outlined throughout these green building programs reference windows and doors. The most specific requirements for window and door products appear in the Energy & Atmosphere section of the LEED for Homes document.

This section offers two basic paths—EA 1 or EA 2 through 6—to meet the program's energy efficiency goals. EA 1 does not cover specific elements of the home, such as windows and doors, but simply requires the overall performance of the home to meet the performance requirements of an Energy Star home. Up to 34 credits are earned for exceeding those requirements.

Although EA 1 does not specify high-performance windows and doors, it is likely that they would be used to meet or exceed the Energy Star for home requirements.

EA 1 also notes that passive design can be modeled and used to take credits under the performance-based approach. Shading strategies are also mentioned.

EA 4—The second path sets minimum requirements for individual elements of the home, as well as methods to earn additional credits. EA 4 covers windows specifically and it is important to note that it does not reference the minimum requirements in Energy Star windows, doors and skylight program, but the minimum requirements set in the Energy Star for Homes national builder option package in Table 1.

LEED Referenced Energy Performance Requirements
  Energy Star Zone
 MetricNorthernNorth CentralSouth CentralSouthern
4.1 Good windows
Prerequisite
U-factor0.350.400.400.55
SHGCAny0.450.400.35
4.2 Enhanced windows
Optional, 2 points
U-factor0.310.350.350.55
SHGCAny0.400.350.33
4.3 Exceptional windows
Optional, 3 points
U-factor0.280.320.320.55
SHGCAny0.400.300.30
Table 1-LEED for Homes references the above window and door requirements from the Energy Star for Homes national builder option package

 
EA 4.1 sets a prerequisite for "good windows" that states:

►Windows and glass doors must have NFRC ratings that meet window requirements in the Energy Star Home option package.

►Homes in Northern climate zones with a total window-to-floor area ratio of 18 percent or more must meet more stringent U-factor requirements. (U-factor=[0.18/WFA]x[U-factor from Table 1]).

►Homes in Southern climate zones with a total window-to-floor area ratio of 18 percent or more must meet more stringent U-factor requirements. (SHGC=[0.18/WFA]x[SHGC from Table 1]).

EA 4.2 gives two additional credits are available for "enhanced" products with NFRC ratings that exceed those referenced in Table 1.

EA 4.3 gives three credits for "exceptional" products with ratings that "substantially" exceed those same numbers.

EA 4.1 also mentions skylights, requiring them to meet the performance requirements for skylights in the Energy Star for Windows program (not those in Table 1). It also limits the ratio of skylight glazing to conditioned floor area to 3 percent or less.

EA 4 does allows decorative glass or skylight area that does not meet thermal or solar requirements to account for up to .75 percent of window-to-floor area.

ENVIRONMENTALLY PREFERABLE PRODUCTS
In the Materials & Resources section of the LEED for Homes, MR 2.2 sets forth a number of ways builders can earn credits by using environmentally preferable products.

Building components, including windows and some doors can earn .5 point each if they meet one the criteria listed. A single component that meets more than one of the criteria can earn points for each.

Table 24 in the Section 2.2 of the LEED document states that window framing and some doors* are eligible for credits if:

►They feature recycled content . The threshold for recycled content is set at a minimum of 25 percent postconsumer or 12.5 percent postindustrial.

►They feature reclaimed content

►They are made using Forest Stewardship Council-certified wood.

►They are "extracted, processed and manufactured" within 500 miles of the home.

*Table 24 indicates that insulated and garage doors from are excluded from earning these credits.

CONSTRUCTION/DESIGN PRACTICES
In the Innovation & Design Process section, LEED for Homes awards one point for ¡°building orientation for solar design.¡±

ID 1.5 offers 1 point for homes that meet the following four requirements:

►The glazing area on the north- and south-facing walls to be at least 50 percent of the sum of the glazing area on east- and west-facing walls.

►The east-west axis of the home must be within 15 degrees of due east-west.

►The roof has a minimum of 450 square feet of south-facing area that is oriented in a way appropriate for solar applications.

►At least 90 percent of the south-facing glazing must be completely shaded (using shading devices, overhangs, etc.) at noon on June 21 and unshaded at noon on December 21.

LEED for Homes does not detail specific installation steps, but requires homes be tested for air leakage and meet certain requirements. Tighter homes can earn additional credits.

Again, LEED for Homes is not as specific in its requirements, but it also recognizes the importance of durability. The building team is required to complete a Durability Risk Evaluation Form, designed to identify issues related to the building enclosure and then establish procedures that will be taken to address those issues. The home can earn three credits if this durability management process is third-party inspected and verified.

The green building programs could be influential on windows and doors in one other important way. Both LEED for Homes and the NGBS give more points for smaller homes—and typically, when there is less square footage, fewer (or smaller) window and door products are used.

Green building programs may not set specific definitions for green products, but they do provide a number of specific opportunities for window and door manufacturers, distributors and dealers to make their products more appealing to builders of green homes. How many certified green homes will be built and how big a market this could be remains to be seen, but LEED for Homes, the NGBS, and other green building program documents are useful tools for this industry, as they can help companies pinpoint issues of concern to green buyers and even suggest steps to be taken to better address those concerns.