Quad Glazed Window

Quad glazed windows or quadruple glazed windows have four layers of glass sandwiched together over three sealed air spaces. A quad-glazed window can reach an astonishing insulating value of R-15, which is comparable or similar to the R-value of a typical insulated garage door.

Look for argon-filled, low-e coated, Energy Star rated windows with insulated spacers separating the panes.

The insulating value of windows is usually rated by the whole window U-factor and the lower the value, the better. A quad glazed window can have a U-factor as low as 0.07 Btu/hr-sq ft °F (exceeding the Passive House standard).

In Southern, hotter climates, the amount of solar radiation that enters through a window should also be minimized. This is rated by the Solar Heat Gain Coefficient (SHGC) which is a value between 0 and 1. The lower a window's solar heat gain coefficient, the less solar heat it transmits. Energy Star rated windows for Southern climates should be less than 0.25 SHGC.

Quad glazed windows have extremely low heat transfer rates, making your building envelope more energy efficient. They also increase the temperature of the inside surface of the window during the winter. This reduces radiant heat loss from your body and makes you much more comfortable, even in lower room temperatures. And they keep out noise from outside, making your house nice and quiet.

There is a long-standing myth that says that glass acts like a very slow liquid and flows slowly over the years. Evidenced by the fact that the bottoms of window panes in old cathedrals are thicker than the tops. Researchers have proven that this is not true. When glass was produced in prior centuries, one end was thicker and heavier than the other. This thicker and heavier end was always installed at the bottom. Modern glass is consistent in thickness and will stay that way indefinitely.