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Community and Q&A

Windows and insulation

chrisjohnston2112 | Posted in Energy Efficiency and Durability on

A portion of my bedroom ceiling is vaulted into a dormer. The dormer window is energy efficient (low e, etc). The window faces east and when the sun shines the vaulted area is noticeably warmer.

I want to try and insulate the window further. Would a film help, and if so would the film need to be rated by any specific industry standard? I have seen several stained glass films, but don’t know if they would help with energy efficiency. Or, would a honeycomb shade work?

I really want to let the light in while improving the energy efficiency of the existing window, if that is possible. I’m in zone 4a. Any advice appreciated!

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  1. GBA Editor
    Martin Holladay | | #1

    If I understand your problem, your bedroom overheats on sunny days.

    You may be right that the problem is due to solar heat gain through the window glazing. But it's also possible that your sloped ceiling is poorly insulated, and that the heat enters your bedroom whenever the sun heats up your roofing. It's quite common for sloped ceilings to be poorly insulated and poorly air sealed.

    Although you mentioned that your window has a low-e coating, you didn't mention its solar heat gain coefficient (SHGC). What you want is a window with a low SHGC. If you are convinced that your window has the wrong glazing, you can order a new window sash with better glazing. You probably want a window with a whole-window SHGC of 0.28 to 0.37 or a center-of-glass SHGC of 0.20 to 0.27. Lower is better than higher. For more information on glazing specifications, see All About Glazing Options.

    If you suspect that your sloped ceiling is poorly insulated, you'll have to remove the gypsum drywall to solve the problem. For more information, see How to Build an Insulated Cathedral Ceiling.

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