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Community and Q&A

Radiant Barrier Warming House?

rocko62580 | Posted in GBA Pro Help on

I installed a foil bubble double sided radiant barrier over the attic rafters in my townhouse. I didn’t measure temperature in the attic prior to installing, however, since the radiant barrier was installed it seems to get very hot in the attic during the day, and that heat seems to be keeping the house warmer.
Today the temperature outside is 85 and my attic is measuring 103. Would it be possible that heat from the outside, other townhouse units and/or the house is getting trapped on the ceiling side of the radiant barrier? At night the attic cools off nicely and by morning it is the same temperature as the outdoors, so I do not believe I have a ventilation issue. Soffits are clear and ridge vent is open.
Is this daytime heating common? Is there a solution to the excessive heating going on during the day? Would an attic fan help? Should I just add more insulation? Thank you!

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  1. GBA Editor
    Martin Holladay | | #1

    1. Don't worry about your attic temperature. Your attic temperature is irrelevant. You don't live in your attic.

    2. If you have enough insulation on your attic floor, it doesn't matter what your attic temperature is.

    3. If your ceiling is too hot on sunny days, it means you don't have enough insulation on your attic floor. So add more insulation!

    Q. "Would an attic fan help?"
    A. No -- an attic fan will just add to your electricity bill, and may suck air-conditioned air out of your house, making things worse. More information here: Are Solar-Powered Attic Ventilators Green? and here: Martin’s Useless Products List.

  2. rocko62580 | | #2

    Thanks Martin for the quick reply. Do you have any idea why the attic seems to be warmer after I installed the radiant barrier? I should add that I am in zone 6, and it gets down to the low 60's at night. I was planning on adding more cellulose, since I compacted most of it while I was installing the radiant barrier, so maybe this is why it feels warmer in the house.

  3. GBA Editor
    Martin Holladay | | #3

    I don't know if your perception is correct, or what the cause might be. But I don't think it matters very much.

    Radiant barriers are not recommended in cold climates like yours.

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