Exterior foam insulation and interior vapor barrier issue?
Last Post 24 Dec 2023 02:53 PM by McLaugh417. 0 Replies.
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24 Dec 2023 02:53 PM
Hello, I am in the process of building a 2500 sqft two store home in Maine (climate zone 6). The current code at a minimum is R 20 cavity, and R 5 continuous on either the exterior or interior. In Maine it is common practice to have the vapor barrier on the interior side of the wall in order to dry to the outside. As im sure most of you know Maine is a heating dominated state. We do have hot summers at times, but we also get bitterly cold winters. Example, the design temperature for heating equipment is 1 degree F in my area. Here is my issue, I have looked at the dew point calculator on CI's website, and found that the R 5 (even though allowable by code) is not sufficient to stop the exterior sheathing from having condensation potential in the winter months. i.e it is not enough to keep it above the dew point. I feel as though there are a couple solutions to this, but I just wanted to hear opinions on best practices on a budget. With the above situation in mind, if the vapor barrier is installed perfectly/continuous, can that mitigate the migration of moisture into the wall cavity so there would not be an issue all together? Or should I just opt to go with a greater R value on the outside of the building, to keep the interior side of the sheathing warm enough in the winter months. Also on a side note...am I causing problems by having an interior vapor barrier (where it should be in our climate), and foam (also a vapor barrier) on the outside? Just doesnt seem like there is any way for drying potential. Here is the wall outside to inside: Foam (R-5 or R10), Tyvek, OSB, 2x6 w/ R-23 Rockwool, 6 mil poly, 1/2 Drywall.
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