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Does glazing thickness really matter?

I am about to have my windows replaced for energy efficiency and have some quotes for the work. 2 quotes are basically the same, triple for the same price as double. However, one company has triple glazing that is 5/8" thick and the other is 1 3/8" thick, so a lot thicker. The thicker glass company also has double glazing at 7/8" thick, which is again thicker than the triple glazing offered by the first company. Does the thickness really matter, is the thicker double glazing better than the thinner triple glazing also?

Any answers most welcome!

Thanks all, Merry Xmas.

Asked by Richard Verreydt
Posted Wed, 12/18/2013 - 22:56

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2 Answers

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Richard,
The best way to compare different glazing options is to compare the specifications shown on the windows' NFRC labels. You want to compare whole-window U-factors (not glazing-only U-factors) and SHGC ratings.

In general, if you are buying double-glazed or triple-glazed windows, a thicker insulated glazing unit (IGU) will usually perform better than a thinner IGU.

The gaps between the panes of high-performance triple glazing units are filled with an inert gas, almost always argon. For argon-filled glazing units, the optimal space between glazing layers is ½ inch, resulting in a triple-glazing unit thickness of 1 3/8 to 1 1/2 inch. Because thicker glazing units can be difficult to integrate into manageable sashes, some window manufacturers promote triple glazing units as thin as ½ inch. Such thin-gapped glazing units perform better with krypton gas than with argon gas. However, since krypton costs more than argon, some window manufacturers only offer argon, even in their thin glazing units; caveat emptor.

It is difficult to design a double-hung or slider window that accommodates full-thickness (1 3/8” or 1 1/2”) triple glazing. Many manufacturers interested in window performance, including Accurate Dorwin, Fibertec, Inline, and Thermotech, prefer to stick with full-thickness triple glazing, and therefore offer triple glazing only for casement, awning, or fixed windows. Those looking for triple-glazed double-hungs have to settle for a compromise product with thin (½” or 1”) triple glazing. As long as builders remember to specify krypton gas, not argon, such thin glazing units can perform well.

The bottom line: compare window U-factors, which show the performance achieved by the whatever type of glazing has been used.

For more information, see:

All About Glazing Options

Choosing Triple-Glazed Windows

Answered by Martin Holladay, GBA Advisor
Posted Thu, 12/19/2013 - 06:50

2.
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Another issue to consider is sound transmission. All else being equal, a heavier piece of glass will block sound more efficiently than a lighter (thinner) one. Some manufacturers publish the STC rating of at least part of their offering.

I should add that all the heavy glass in the world won't do you any good if your wall, your window, or your window opening are air-leaky, since sound will simply go through the leaks instead of being blocked by the material.

Answered by Alexandre Richer
Posted Thu, 12/19/2013 - 14:54
Edited Thu, 12/19/2013 - 15:01.

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