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is it a good idea to put foamboard covered with aluminum foil on top of windows in my attic?
(gregtech.eu)
Pretty much the title. It get quite hot here in Europe.
this post was submitted on 10 Aug 2026
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If you have single pane windows, the foil needs to be on the outside of the window or you run the risk of shattering the glass. If it's a double of triple pane you can place it on the inside.
Very good to know, thanks
That is a fantastic tip I would have never considered but yeah, that's gonna be a big temperature differential!
Why is there only a risk of shattering with a single pane window?
More panes = more mass. More mass = lower average temperature. Lower average temperature = less chance of sudden cracks or shattering
Hmm, but don't you think that over the entire day they'd heat up to the same temp? Sure, more mass, but that just means it'll take longer to heat up to the same temp as the single pane. And I assume the day is long enough.
Sudden shatter happens when something is heated or cooled so quickly that parts of it expand or constrict at different rates. Since the larger thermal mass of the thicker glass will spread the heat more, it won’t heat up as quickly, thus reducing the chance of a sudden shatter. It may well reach the same temperature, but doing so over a longer period is still safer
I've had old double glass shatter as well after putting them on the inside. Best to just always put them outside.