Building Codes Assistance Project

As the primary barriers between a home and the outdoors that cover the openings of the building envelope, high performance windows, doors, and skylights (fenestration) are essential to an energy efficient home. Choosing such products involves several considerations, including appearance, energy performance, human factor issues, technical performance, and cost. Other factors like building orientation, natural and artificial shading, and climate will influence the properties selected for windows, doors, and skylights installed throughout the home.

The first residential building energy codes adopted by many states were the 1992, 1993 and 1995 versions of the Model Energy Code (MEC), the predecessor of the International Energy Conservation Code (IECC). Today, many energy codes contain prescriptive requirements include the fenestration product minimum performance criteria (U-factor, Solar Heat Gain) based on climate zones. Some energy codes also provide trade-offs permitting more fenestration area if these products are more energy efficient.

Dramatic improvements in fenestration technologies in recent years have revolutionized performance. A good example of this change is the adoption of Low-E window technology in the 1990s, a period when almost all windows installed in homes were clear glass. By 1995, the first national standard for measuring solar heat gain co-efficient (SHGC) for windows was developed. When minimum SHGC ratings were first incorporated into energy codes in the year 2000, most manufacturers were no longer making clear glass windows. Technology had transformed the market faster than national codes could incorporate the new standards.

Today, high performance windows, doors, and skylights provide myriad benefits, including:

• Lower energy bills
• Better views and ambiance
• Increased comfort
• Less condensation
• Less fading
• Lower maintenance expenses
• Positive energy tradeoffs

Resource Center -- Terms to Know:

U-value: A measure (Btu/h-ft2-°F) of how well a material or series of materials conducts heat. U-factors for window and door assemblies are the reciprocal of the assembly R-value. The smaller the number, the less the heat flow.

Window U-factors typically range from 0.2 to 1.2, while the U-factors of other building assemblies (e.g. walls, floors) typically range from 0.02 to 0.10 when insulated. Using efficient windows decreases the energy consumption of the structure and helps the project comply with the code.

SHGC: Solar heat gain coefficient (SHGC) is the glazing's effectiveness in rejecting solar heat gain. SHGC is part of a system for rating window performance used by the National Fenestration Rating Council (NFRC). SHGC is gradually replacing the older index, shading coefficient (SC), in product literature and design standards. If you are using glass whose performance is listed in terms of SC, you may convert to SHGC by multiplying the SC value by 0.87.

The solar heat gain coefficient (SHGC) for your window may be found on the National Fenestration Rating Council (NFRC) label affixed by the window manufacturer prior to sale.

There are several resources for selecting fenestration products available to consumers, builders, and designers. ENERGY STAR provides purchasing tips and information on rebates.

The Efficient Windows Collaborative (EWC) is a consortium of industry manufacturers and suppliers whose website has a window selection tool to compare different options for dozens of locales.

The National Fenestration Rating Council provides a directory of certified products and certified program participants.

There are also many new and innovative fenestration products available at www.BuildingGreen.com.

The following section provides examples of these types of code improvement language or methodologies in these areas.

 Policy Options

Coming soon!

**Image 1 courtesy of Building Energy Codes Resource Center. Images 2 and 5 courtesy of the Efficient Windows Collaborative. Images 3 and 6 courtesy of the National Fenestration Rating Council. Image 4 courtesy of U.S. EPA Energy Star.