What Are Double-Paned or Double-Glazed Windows?

Double-paned, or double-glazed, windows are the standard type of window in most residential building and remodeling. Once the norm, single-paned windows are rarely installed anymore.

There is no contest when comparing single- to double-paned windows. Double-paned windows offer stellar energy efficiency, better soundproofing, and increased interior comfort.

What Is a Double-Paned Window?

A double-paned window has two panes of glass set into a frame. Between the glass is an intervening gas or air pocket to better insulate a room. This window is sometimes called a double-glazed window.

Double-paned windows are now standard for both new construction and replacement windows. Triple-paned windows are sometimes recommended in environments with harsh weather for maximum insulation.

Another term for a multi-layer window is insulating glass unit (IGU), which also reflects its cohesive nature.

Advantages of Double-Paned Windows

The gap between glass in a double-paned window is filled with a safe gas such as argon, krypton, or xenon, increasing the window's resistance to energy transfer.

This gas, denser than air, is the barrier against outside temperatures that single-paned windows cannot offer.

• Argon: Argon is a common and most affordable type of gas.
• Krypton: Krypton is typically used in triple-paned windows because it performs best within extremely thin gaps.
• Xenon: Xenon, denser than argon or krypton, costs the most and is not as commonly used for residential applications.

What R-Value Means For Double-Pane Windows

R-value measures the material's resistance to energy transfer. The higher the R-value number, the greater the resistance and the higher the insulating value of the window.

Most windows have a special low-E (low emissivity) insulating film on the glass that adds to the R-value. The film reflects heat energy into or out of the home and it reflects ultraviolet (UV) rays to better protect furniture and artwork from fading.

Number of Panes	Air/Gas	Coating	R-Value
1	None	None	0.9
2	Filled with 1/2-inch of air	None	2.084
3	Filled with 1/2-inch of air	None	3.226
2	Filled with argon	Low-E (1 coating)	3.846
3	Filled with argon	Low-E (1 coating)	5.433

Wall R-Values vs. Window R-Values

With window R-values reaching nearly 5.5, how does that compare to wall system R-values?

A standard two-by-four stud wall with batt insulation and wallboard and wood siding has an R-value of R-12 to R-15, which is considered to be on the lower end compared to other types of materials and sidings.

Window manufacturers continue to develop technologies that will allow windows to more closely approach the higher R-value of walls. Still, walls will always provide better energy efficiency than windows.

Tips for Improving Window Efficiency

No matter how well-designed they might be, double- and triple-paned windows can always be helped along to eliminate energy loss. Here are tips to help improve the efficiency of your windows:

• Use thermal curtains. Thick thermal curtains drawn across the windows at night significantly raise the window's overall R-value.
• Add window insulating film. Apply a thin clear layer of plastic insulating film to the window frame with adhesive. Heat the film with a hairdryer to tighten it.
• Weatherproofing. Older windows may have hairline cracks or they are beginning to open up around the framing. Those problems let cold air enter the home. Using an exterior-grade silicone caulk can close up these leaks.
• Replace a foggy window. Windows that are foggy between the two panes of glass have lost their seals and the gas has leaked out. It is usually best to replace the entire window to regain the energy efficiency in your room.
• Fill in the window. Windows in disused or rarely used areas waste energy, with little benefit to show for it. If the window has little value as a window, fill it in with an insulated wall system. First check with your local permitting office to ensure this is allowed since some areas, by code, must have egress to the exterior.