Window Durability

Frame and sashes

Design and workmanship may be the most important factors determining the long-term durability of sashes and frame. However, some general statements can be made about the durability aspects of different frame materials:

• Aluminum: Strong and durable, but readily conducts heat. Condensation and even frost can form. Thermal breaks reduce conduction and improve condensation resistance. The durability of thermal breaks varies by type and quality.
• Wood: Easy to repair and maintain. Intrinsically susceptible to rot, but many new wood windows are protected by a durable exterior finish or cladding. Cladding should prevent moisture from forming underneath.
• Composite: New wood/polymer composites are very stable. Better moisture and decay resistance than conventional wood.
• Vinyl: Good moisture resistance and low maintenance. Tends to expand or contract as temperature changes, but recent designs have improved dimensional stability and resistance to UV radiation and temperature extremes.
• Fiberglass: Strong, durable and dimensionally stable.

See more detailed information on frame types.

Insulating glass

The durability of insulating glass (IG) units is critical to window energy performance. Seal failure leads to the loss of insulating gas and can result in condensation from moisture penetrating between the panes, which can degrade low-E coatings.

To minimize the likelihood of seal failure and gas loss, insulating glass in ENERGY STAR windows must be certified through recognized programs. IG certification requires that sample IG units undergo accelerated weathering over extended time periods to determine whether the IG unit can withstand extreme temperature swings, high humidity and UV radiation without failure. IG certification also requires that the manufacturer implements in-house quality assurance.

Field studies have shown that insulating glass failure rates differ greatly depending on the quality of seal systems and manufacturers' quality assurance. Well-fabricated IG units can retain gas at a loss rate of less than 1 percent per year, resulting in only minimal loss of insulating performance.

Most manufacturers offer a warranty against insulating glass failure which varies from a limited period to the lifetime of the window. A range from 10 to 20 years is common.