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Small Cabin Forum / Cabin Construction / Laminated 2x8 walls and foam insulation
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# Posted: 10 Feb 2024 14:29

We will be building a cabin this year on our property in north Idaho. In the 90s we built a cabin out of 3 laminated 2x10s very similar to the 2x8 version I saw on this web site, by Stoney.
While our 2x10 cabin did great, I would like to add a layer of foam insulation in the lamination this time. Having spent a considerable amount of time studying R-value and thermal mass, I’m thinking about adding a layer of 1.5” rigid foam between the outer 2x10 and the center 2x10. My thinking is that this would increase overall R value while allowing the inner and center 2x10 to act as thermal mass. My engineer friend thought that perhaps the foam insulation should be placed between the inner 2x10 and center 2x10, in creasing initial R value.
I’d appreciate hearing from others who are knowledgeable in this area.

# Posted: 10 Feb 2024 16:35

Thermal mass in the conditioned area of a cabin can be sorta counterproductive if the cabin is part-time use in cold weather. It takes time to raise all the interior mass from the cold ambient temperature to the desired living temperature.

What about building a 2x4 wall and using just layers of foam on the exterior, then lap-siding with a rainwall technique? Or a 2x8 stud wall with blown-in dense pack cellulose insulation in the stud bays.

# Posted: 10 Feb 2024 16:44

Typical blue or pink 1" styro is said to be an R5.
Soft wood has better R than hardwood, and wood varies quite a bit. S yellow pine I think is like R1.4/inch?
You might get close to an R10-12 with a 3 plank lam sandwiching 1" styro? Iirc code is spec'ing min R14 now.

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