Insulating unfinished basement
shumaker76
| Posted in Energy Efficiency and Durability on
Unfinished basement that will remain unfinished. 6ft deep with 2ft above grade. Located in central Ohio, zone 5.
Is Thermax available as repurposed?
Any repurposed insulation recommendations for central Ohio?
If multilayered, does Thermax have to be the final layer or all layers?
Thanks
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What means "repurposed" in this context? (Reclaimed? Recycled?) The primary use for Thermax is insultion, and that seems to be your primary purpose here too.
In zone 5A it takes 3" to meet IRC code-min with polyiso. If you wanted to use 2" of Brand-X or reclaimed roofing iso against the foundation and use fire-rated Thermax for the layer facing the interior to meet local fire safety codes that works. If using foil-faced iso on the interior side layer it's better to use foil-faced goods for the rest. Fiber faced roofing iso won't reject ground moisture as well as foil does, and could slowly load up without the drying path to the interior.
Reclaimed. 650sqft of wall surface. I might have issues with the small quantity needed?
If you can get some reclaimed eps, why not get that and then put the foil faced Thermax over the top of that to achieve your R value?
Does 3" of EPS with 0.5" of Thermax sound about right? What type of facers are needed on the EPS?
I think the ratings on Thermax being adequately fire protected are only for specific assemblies with polyiso foam as the only foam protected by its skin, up to a specific thickness of polyiso. So a strict code official might not accept any layering of EPS and Thermax without drywall over the whole thing. But certainly 0.5" of Thermax would provide some degree of fire protection for the EPS. If I had a low-cost source of EPS and not Thermax, I think I'd be inclined to just cover EPS with drywall, rather than worrying about the safety and code compliance issues of a mixed stack.
Any recommendations regarding Dow Thermax vs JM CI-Max in this application?
Always be careful with foam in basements. Termintes love it. That aside getting the top portion of the basement wall above the frost line is good enough at r8 open cell panels. Talking most bang for the buck. Means five foot of the six covered. The ground temp below the frost line makes insulation below that less of an issue. Only if you have a lot to spend with little return would I go for the full treatment. As always fix any moister issues which most older and even new basement have first. And meet fire code.
Stephen,
Your advice is a little hard to decipher, but it sounds as if you are recommending that the wall insulation shouldn't extend all the way down to the floor. This is bad advice, since concrete is a thermal conductor. If you leave some of the concrete peeking out near the floor, uninsulated, you have left a large thermal bridge.
To ensure that you have no thermal bridges in your basement wall system, the wall insulation should extend from the top of the basement wall all the way to the basement floor. Here is a link to an article with more information on this issue: How to Insulate a Basement Wall.