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spray in foam insulation in attic rafters

Posted by bhebert (My Page) on
Sat, Aug 14, 10 at 11:09

I am considering having spray in foam insulation installed in our attic rafters. I have a 1950s ranch style home with a low pitched roof. Attic temps can be extreme in the summer months. I live in southeast Texas where the average summer highs can reach 95 degrees with 80-90% humidity.
I have a few questions regarding the effectiveness of this technique. When the foam is sprayed in, should it cover all ventilation effectively making the attic conditioned space? I have read that if spray in insulation is used the attic should be sealed off. I have also heard that this can damage the roof sheathing causing it to rot? The attic is currently vented with soffit vents and ridge vents.

There is also a company that installs spray in radiant barrier. This method would keep the attic ventilated but cuts back on the radiant heat coming in from the underside of the roof sheathing.


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RE: spray in foam insulation in attic rafters

Hi,
I think that the approach of spraying foam under the roof rafters, and making the attic space part of the conditioned space of the house is a good one if done carefully.
Seems like it would be a time consuming job to block all the current attic ventilation carefully.

If you use closed cell foam, I don't see why there would be any moisture or condensation problem with the roof sheathing.
Some of the people who make roof shingles don't like insulation right under the sheathing because it makes the sheathing and shingles run hotter and may reduce their life -- some people think this is bunk.

If you have ducts or AC equipment in the attic, moving the insulation line up to the roof rafters will make your AC and duct system more efficient. The FSEC has some papers on what kind of saving results from this.

Have you thought about just blowing additional cellulose insulation on the attic floor? Seems like this would be a lot cheaper, and may accomplish about the same result?

http://www.homeenergy.org/archive/hem.dis.anl.gov/eehem/97/970504.html

Gary


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