Helping Green Builders (and Remodelers) Score Points

What LEED for Homes and NAHB's Green Building Standard say about windows and doors
John G. Swanson
April 1, 2008
FEATURE ARTICLE | Codes & Standards, Energy Efficiency

LogoWhat makes a window or door green? An Energy Star label? Certified wood components? Recycled content? Its orientation? Good installation practices? There is no one answer, but all these elements can help a product score points for builders of green homes. 
 
With the green building movement gaining momentum, numerous home rating programs have been started around the country, designed to help architects, builders and even remodelers design and build homes that can be officially labeled "green." While many of these programs are well established at a regional level, two national programs are now being rolled out and are attracting plenty of attention. Neither sets a specific standard for a green window or door product, but both could change the way windows and doors are selected and installed in the home.

USGBC AND NAHB

shadeLast fall, the U.S. Green Building Council officially launched its LEED for Homes third-party certification system following a two-year pilot program. Originally implemented in the commercial building market, USGBC's Leadership in Energy and Environmental Design green building rating systems have gained widespread acceptance in the market. Backed by a number of environmental groups, LEED certification has become a requirement for government-owned and funded buildings at the local, state and federal levels.

At the International Builders Show in February, the National Association of Home Builders officially launched its National Green Building Program. Working with the International Code Council, NAHB, through its NAHB Research Center, is developing the National Green Building Standard. Based on the National Green Building Guidelines, the standard is expected to be approved by the American National Standards Institute this spring. In the standard development process, the guidelines have been enhanced to include residential remodeling, multifamily building, and lot and site development; and to reflect advancements in the International Residential Code, NAHB points out.

bronxBoth the LEED and NAHB programs have their supporters and detractors, but they are structured in similar manners. Each rating system establishes certain requirements and outlines numerous specific steps builders can take to earn points.  The LEED program 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. It establishes a minimum level of performance through prerequisites in each category and rewards points for improved performance. LEED sets four performance tiers-certified, silver, gold or platinum-according to the total points earned. Like the Guidelines that they are based on, the new NAHB/ICC standard requires builders to include features in seven categories: energy, water and resource efficiency; lot and site development; indoor environmental quality and homeowner education. Table 1 shows how the point system works in the existing guidelines, but a new higher emerald level is being added to the bronze, silver and gold certification levels when the new standard gets issued.

Both green building programs require third-party verification for a home to be certified. USGBC works through a network of LEED for Homes Providers that provide technical, marketing and verification support to builders. Under the NAHB program, homes are inspected and verified by local green experts and the documentation is sent to the NAHB Research Center for review and certification. The NAHB program incorporates requirements and rating procedures for remodeling and home additions, as well as new homes. USGBC is working to launch a separate ReGreen program with guidelines for remodeling existing homes. 

ENERGY PERFORMANCE REQUIREMENTS

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, not surprisingly, appear in the sections of both the LEED for Homes and National Green Building Standard documents covering energy efficiency. 

LEED for Homes offers two basic paths to meet the programs energy efficiency goals. The first does not cover specific elements of the home, but simply requires the overall performance of a home to meet or exceed the performance of an Energy Star home. The second path sets minimum requirements for individual elements of the home, as well as methods to earn addition credits. Section EA4 covers windows, and it is important to note that it does not reference the Energy Star windows, doors and skylight program; instead it references the Energy Star for Homes national builder option package (Table 2). It 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 2]).

- 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 2]).

A builder can get two additional credits for "enhanced" products with NFRC ratings that exceed those referenced in Table 2 and three credits for "exceptional" products with ratings that "substantially" exceed those same numbers.

This same EA4 section also mentions skylights, requiring them to meet Energy Star skylight requirements (not those in Table 2). It also limits the ratio of skylight glazing to conditioned floor area to 3 percent or less. One final note on EA4-it 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.

The National Green Building Standard also features two compliance paths to achieve its energy efficiency goals-one performance-based and one prescriptive. The same energy performance requirements for fenestration products are mandatory for both approaches, however. Section 701.4.6 of the second draft says that windows, exterior doors, skylights, and tubular daylighting devices must have NFRC-certified U-factors and SHGCs in accordance with Energy Star or equivalent, or those figures shown in Table 3. There is an exception for decorative fenestration elements up to 15 square feet or 10 per of the total glazing area, whichever is less. 

Under the performance-based approach, builders might be encouraged to use higher-performing windows and doors, as they can earn additional points by exceeding the requirements of the International Energy Conservation Code. The prescriptive approach in the document also outlines two sets of "enhanced fenestration specifications" that can earn builders additional points, also shown in Table 3.

MANAGING THE SUN
NAHBIn addition to specific requirements, both the NAHB and LEED programs encourage the use and management of the sun's energy with credits for passive solar design, daylighting and solar protection. The use of "sun-tempered design," for example, is worth five points, according to the draft NGBS. Covering building orientation, sizing of glazing, and design of overhangs, the requirements for sun-tempered design include the following:

- The long side (or one side if of equal length) of the building must face within 20¡ of true south;

- Vertical glazing area is between 5 and 7 percent of gross conditioned;

- Floor Area on the south face and windows have an SHGC of .40 or below;

- Vertical glazing area is less than 2 percent of gross conditioned floor;

- Area on the west face, less than 4 percent on the east face and less than 8 percent on the north face;

- Glazing must be Energy Star compliant or equivalent;

- Where installed, skylights must be installed with shades and insulated wells, all glazing must meet Energy Star specifications;

- Horizontal skylights must be less than 0.5 percent of finished ceiling area, and sloped skylights on slopes facing within 45¡ of true south, east or west must be less than 1.5 percent of finished ceiling area;

- Overhangs or adjustable canopies, awnings or trellises must be used to provide shading on south-facing glass for the appropriate climate zone. The document spells out different overhang depths, depending on the vertical distance between the bottom of the overhang and the top of the window sill, and the different climate.

In addition to designing a home to benefit from solar heat, the NGBS award points for "passive cooling design features." Three points can be earned by taking two or more of a number of steps, including exterior shading on east and west windows through the use of moveable awnings or louvers, covered porches, vine-covered trellises or attached or detached structures such as sheds or garages. Other strategies include overhangs designed to provide shading on south-facing glazing and placement of windows and/or venting skylights to facilitate cross ventilation.

Different ways to maximize a home's use of the sun to reduce energy demand are rewarded as well. Automated solar protection that provides shading for windows earns one point. Two points are awarded for the use of tubular daylighting devices or low-E insulating glass skylights in rooms without windows.

LEED for Homes awards one point for "building orientation for solar design" in its section on integrated project planning. This credit requires 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. 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. Other requirements for this credit cover building orientation and enough south-facing roof area to take advantage of solar applications. 

Section EA1 of the LEED document, which covers energy efficiency, simply notes that passive design can be modeled and used to take credits under the performance-based approach. Shading strategies are also mentioned. The performance path awards credits for "exceptional energy efficiency," performance that exceeds the Energy Star for Homes program standards.

EXTRA CREDIT

Green building programs seek to reduce waste, encourage use of renewable materials and create a healthy indoor environment. As a result, window and door products can also earn credits or score points for builders based on their content, finishing requirements, the location where they are made, and the manufacturer's operating practices, based on the LEED and NAHB programs.

Recycled content in building products, for example, is acknowledged in both programs. The NGBS awards one point if two "minor components" feature 25 to 50 percent recycled content, two points for two minor components with 50 to 75 percent recycled content and three points when recycled content is greater than 75 percent in two minor components. For "major components," the potential points for recycled content double. The draft standard does not say whether windows or doors would be classified as major or minor components of a building, however.

In the section of the LEED document covering materials and resources, there is a list of "environmentally preferable products," which references recycled content. A table specifically lists window framing and doors-although it excludes insulated and garage doors-as products that can earn half a point per component for recycled content-with the threshold set at a minimum of 25 percent post-consumer content or 12.5 percent postindustrial. The same credits apply to "reclaimed" products.

As noted, a manufacturer's plant location may also enable a product to earn credits. Recognizing the benefits of limiting energy demand involved in transportation of products, LEED offers a half point per component credit for were "extracted, processed and manufactured" within 500 miles of the home. Again, window framing and doors- excluding insulated and garage doors-are said to be eligible for this credit.

As USGBC has developed its LEED documents over the years, it's been evident that some of its membership would like to discourage the use of vinyl products. No specific material is specified as "environmentally preferable" for windows and doors in the LEED for Homes program. It does, however, award a half point credit for window framing and doors using wood certified by the Forest Stewardship Council.

The National Green Building Standard takes a different stance, awarding builders points for the use of building materials "derived from renewable resources." Up to eight points can be earned for using "biobased" products, including certified solid wood, engineered wood, bamboo, straw, and other natural fibers. The points awarded are determined by the percentage of the projected building material cost.

Whether windows and/or doors could qualify is not spelled out, but NAHB's draft document also award four points to builders using a minimum of two certified wood-based products in major elements of a home. NAHB recognizes a number of wood certification programs besides the Forest Stewardship Council, including the Sustainable Forestry Initiative, the American Tree Farm System and the Canadian Standards Association's Sustainable Forest Management System Standards.

Windows and doors can earn points in at least two other ways under the NGBS.  The document currently awards points for using building materials or assemblies that do not require site-applied finishes. In this section, it specifically cites "window, skylight, and door assemblies not requiring paint or stain on exterior and/or interior surfaces."

It also awards points for purchases from product manufacturers with operations and business practices that incorporate environmental management system concepts. The standard says the production facility should be ISO 14001 certified or equivalent and offers one point for every 1 percent of the estimated total materials cost coming from such production facilities, with a maximum of 10 points possible.

CONSTRUCTION PRACTICES
Both the LEED for Homes and NGBS documents offer numerous other requirements and credits that could have an impact on windows and doors. Both programs address installation practices with requirements for reduced air leakage.

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. In its section on reducing air leakage, the NAHB document specifically requires that, "caulking, gasketing, adhesive flashing tape, foam sealant, or weatherstripping is installed forming a complete air barrier" around windows and doors.

The NAHB standard also awards practices that provide, "enhanced durability and reduced maintenance." In this section, it awards three points for an exterior door assembly, including sidelites, that is covered and protected from the effects of precipitation and solar radiation. This can be done through the use of a porch roof or awning, extending the roof overhang or recessing the exterior door.  Additional covered door assemblies can earn an additional point.

The same durability section of the document also awards six points when a builder shows flashing details in a home's plans and flashing is installed around exterior fenestrations, skylights and doors and other applicable areas, such as roof valleys and various intersections. To earn these points, a drip cap must also be provided above windows and doors that are not covered by a roof overhang or protected some other way.

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 or remodeled in future years 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. W

HOW DOES LEED CHANGE WINDOWS AND DOORS?
More than 300 homes have been certified under the LEED for Homes program since it launched as a pilot in 2005. Another 8,000 homes are said to be in the pipeline. We asked representatives of two LEED for Homes Providers-organizations that assist builders in meeting these green building requirements and the rating and certification process-about windows and doors used in green homes.

Both Eric Martin of the Florida Solar Energy Center in Cocoa, Fla., and Bill Dakin of the Davis Energy Group, in Davis, Calif., say superior energy efficiency is the number one priority for windows and doors in the projects they've been involved with, but both list other concerns as well. "Do not diminish the importance of recycled and reclaimed material properties that are also given credit in the rating system," says Dakin. The goals of reduced air infiltration and reduced maintenance are also factors.

Martin agrees that the list of issues examined in selecting windows and doors goes beyond energy efficiency. He cites UV rejection, use of windows as part of passive solar daylighting plan, the presence of "green" materials in the window product such as recycled content or certified sustainable wood, and the distance between the place of manufacturing to home site as factors that are considered.

Neither sees the LEED guidelines necessarily changing the number of windows and doors used per home, but builders are looking closely at the performance numbers. "Every LEED Home is different," Dakin reports. Many custom homes are designed with passive solar features. In these cases, the key is finding windows with low U-factors but higher SHGC to maximize daylighting and solar gains during the winter, while architecture is used to minimize cooling loads. In these cases, Dakin says the builder usually needs to go with a custom window manufacturer, since many stock windows sold in California are not tuned for this purpose. "In production homes," he continues, "we are seeing LEED builders specifying high performance windows with low SHGC since optimizing window orientation is difficult to achieve in a production setting."

"In Florida we look to reduce solar gain basically year round," Martin reports. This means building orientation, available shade from architectural features and site features, and window to floor (or wall) area ratio are all carefully considered in LEED homes.
Both providers also state that, generally, when dealing with window and door manufacturers and/or dealers, LEED designers must be able to find the technical support they need to answer questions and make optimal use of these products. "Being able to locate the NFRC ratings for the windows online is important for the consultants and design team to properly evaluate the building performance," notes Dakin. "Some manufacturers are better than others."

When it comes to evaluating the energy efficiency of windows and doors, both put a great deal of emphasis on the NFRC ratings. "For me, it's the performance numbers," Martin states. "Whether they represent efficiency beyond Energy Star is really up to the overall efficiency goals of the project."

"An Energy Star label doesn't mean much to builders; maybe to homeowners. NFRC performance numbers," he adds, "have more value to the design team."

As far as green building needs that are not being adequately addressed by the window and door industry, both suggest potential areas for product development.  "It is difficult to find windows with low U-factors and higher solar heat gain coefficients," states Dakin. "You can get custom tuned windows, but at a premium." Given the additional concerns of his market, Martin suggests, "I see a need for more products that have both superior energy efficiency and impact resistance."