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Question DetailsAsked on 11/19/2014

Tripple pane window: if window needs to be tempered, can just the interior pane be tempered to follow code?

Buying Pella Designer series with blinds between glass. This window has double pane then blinds, then third pane on interior. To follow international code, if window needs to be tempered, can just the interior pane be tempered or do all three panes need to be tempered?

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1 Answer


There are a few exceptions for louvered windows, bulletproof/unbreakable security glass, wire mesh glass, structural glass, and the like - but generally, tempered/safety glass is designed to break into lots of little bits of glass rather than into angular penetrating and slicing shards, but will still break when hit - it is not designed to actually prevent penetration by a body. Therefore, again with a few unusual exceptions that generally do not apply to residences, if the pane exceeds 1 SF in area ALL the layers have to be tempered if the location calls for tempered glass.

IRC (International Residential Building Code) section R308 covers this. If less than 1 SF, then other layers not directly exposed to the threat of being hit have to be made conforming to and be labelled as CPSC 16 CFR 1201 or ANSI Z97.1 to be allowed.

And of course, if the threat comes from both sides, like say a glass panel in a door (or glass door) or sidelight, then the outer pane on BOTH sides has to be tempered regardless.

Oh - and there is an interesting provision that if the window is more than 25 feet above the ground (without an outside balcony or such) evidently it is exempt rom the otehr panes being tempered, as I read it - guess they figure it doesn't matter how cut up you get if you break past the first pane because the fall will get ya.

Answered 5 years ago by LCD

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