attic temp in retrofit with spray foam

momwalkinJune 15, 2011

We recently converted our attic to an unvented attic with spray foam insulation on the roof deck. We live in a hot humid climate and our hvac system was in the attic space. Our attic temperature is averaging about 12 degrees higher than the temperature inside our home. We have friends who built a new home and used spray foam and their temp difference is no more than 5 degrees. About 75% of our attic space was floored so we did not remove the cellulose insulation in that area but we did remove the cellulose where the attic was not floored. Though our energy bill has decreased we have not seen the savings we thought we would. Is 12 degree difference typical for a retrofit? Should we remove all the cellulose to get a cooler temp in the attic? We did install an ac duct into the attic space as we were oversized on one of the units. Any advice would be greatly appreciated.

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The color, ventilation and type of roof has a greater impact on the attic temperature. For example, a asphalt shingle roof can be hotter than a metal roof by over 10 degrees celsius or 50 degrees F (my own measurements).

The thickness and evenness of the spray foam application probably has some impact too.

Removing the cellulose attic insulation is not the way to go as your living space will become hotter.

    Bookmark   June 15, 2011 at 12:26PM
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The temp difference in Fahrenheit should be 22 not 50 (direct conversion of 10 C to F)

    Bookmark   June 15, 2011 at 11:23PM
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Why do you want your attic so cool? Where did the projected energy savings figures come from? YOu are comparing electricity consumption this year compared to last year, I assume, so ask yourself, is it hotter this year than last year?

    Bookmark   June 17, 2011 at 8:01PM
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Windows on Washington Ltd

What was the applied thickness of the foam and type?

    Bookmark   August 22, 2011 at 12:50AM
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