Insulation questions for new construction in northern part of Zone 3
Hey everyone, I want apologize in advance for my ignorance on the matter…
I am getting ready to start construction on a new home in Northeast Oklahoma, which is in the northern part of climate zone 3. I have been loosing sleep at night from reading all different kinds of articles about how I should insulate my forever home.
The house is 2,700 sq/ft of conditioned space with cathedral ceilings throughout. (Which is part of my internal debate…) So after a LOT of reading, here’s what I THINK I should go with.
2×4 walls filled with open cell foam and trimmed with 1″rigid foam over the exterior sheathing. My question on the walls is, should I have an exterior water barrier between the rigid foam and sheathing? I’m thinking yes. Also, do I need an interior vapor barrier? Retarder?
Now as for the roof. Since this house is a full cathedral ceiling, how should I go about the insulation in it? I am reading that open cell foam directly on the sheathing could lead to decking rot. So I’m thinking just closed cell to the depth to get the desired r value. But I’m just not sure.. That’s why I’m here for input from the experts. I will attach a couple images of the layout so you can see the build type. Thanks in advance everyone!!
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Replies
Colter,
Q. "Should I have an exterior water barrier between the rigid foam and sheathing?"
A. Every wall is required by code to have a water-resistant barrier (WRB) -- usually plastic housewrap. In your case, the housewrap would usually be installed either (a) between the sheathing and the rigid foam, or (b) on the exterior side of the rigid foam. Here is a link to an article you should read: Where Does the Housewrap Go?
Q. "Do I need an interior vapor barrier? Retarder?"
A. In your climate zone, you don't need an interior vapor retarder. Interior vapor barriers aren't required anywhere except under concrete slabs. For more information, see Do I Need a Vapor Retarder?
Q. "This house is a full cathedral ceiling, so how should I go about insulating it?"
A. Read this article, which will answer all of your questions: How to Build an Insulated Cathedral Ceiling.