Much of a building’s heat transfer occurs through its windows. Therefore, one of the most critical ways to reduce heat loss (or gain) is by selecting the appropriate, high-performance window for the given conditions.

Important window properties include solar heat gain coefficient (SHGC), heat loss coefficient (U-value), and visible transmittance. The appropriate combination of these properties will depend on the climate, solar orientation, and building application.

Ultra-high-performance windows combine multiple glazing layers, low-emissivity coatings, argon or krypton gas fill, good edge seals, insulated frames, and airtight construction.

Because metal is a particularly good conductor, metal window frames need a “thermal break” (an insulating material inserted to block the conductive heat transfer across the metal) to achieve high performance.

High-performance windows have multiple benefits besides saving energy. These include:

• Enhancing radiant comfort near the windows (thereby allowing perimeter space to be used and sometimes enabling perimeter zone heating/cooling to be eliminated).
• Allowing the HVAC (heating, ventilation, and air conditioning) system to be downsized (thereby reducing first costs).
• Reducing fading from ultraviolet light.
• Reducing noise transfer from outside.
• Reducing condensation and related potential for mold and extending the life of the window).
• Improving daylighting—quantitatively and qualitatively.

Related Articles

• Reducing Energy Use in Buildings
• Controlling Heat Transfer in Green Buildings
• Efficient Cooling Methods for Green Buildings

This article is an excerpt from the book Green Building: Project Planning & Estimating which can be purchased through the RSMeans Bookstore.

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