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.

This new 2nd edition has been completely updated with the latest in green building technologies, design concepts, standards, and costs. Includes Means’ Green Building CostWorks CD at no additional cost.

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