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How to convert a non sealed attic space to a sealed attic space in a Zone 3

I'm looking at completely redoing the whole house insulation in a 70 year old home. I'll be gutting the walls for other reasons, and figured redoing the insulation with blown in foam insulation made the most sense. The question I do have is the attic space. The design of the roof is a barn style with the first part of the roof having a very high angle (almost vertical) and the rest of the roof having a normal slope. As part of this, the upper floor of the house "sticks" in to the attic, and there are 2 normal sized doors that lead directly to the attic. Due to the doors and all the nooks and crannies of how the house sticks in to the attic it seems like it would be very difficult to ever properly seal the area. So I was thinking about going to a sealed attic. Right now it's just vented with 2 vents on the upper corner of the roof. I live in Atlanta, basically right at the boundry of zone 3 and 4, with it being in the 3 zone. From reading the R806.5 specs it seems like it's ok without a vapor barrier, but I wanted to get some more opinions on how to go about this (vapor barrier, closed cell vs open cell, etc...) or if it's a very bad idea to go with a seal attic.

Thanks.

Asked by Stephen Saar
Posted Sun, 06/15/2014 - 19:12

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Stephen,
For information on how to turn an unconditioned vented attic into a conditioned unvented attic, see this article: Creating a Conditioned Attic.

Concerning your question about vapor barriers: closed-cell spray foam isn't very vapor-permeable, while open-cell spray foam is vapor-permeable. However, airtightness matters more than vapor permeance, so I wouldn't worry very much about this issue. I don't advise you to install interior polyethylene in your climate. For more information, see Do I Need a Vapor Retarder?

Answered by Martin Holladay, GBA Advisor
Posted Mon, 06/16/2014 - 06:35

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