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Small Cabin Forum / Cabin Construction / Felt underlay as insulation?
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# Posted: 10 Sep 2012 12:06

We've been going over our floor and roof insulation options, and I'm thinking it might be for the best to just go with what our plans say to go with. So, our plans have 30# felt under the subfloor of the main cabin room, and 2" urethane in the floor of the loft (the part that is over the porch, the interior part of the loft is uninsulated, of course). For the roof it says "metal roofing or optional 5/8" CDX w/15# felt and asphalt shingles".

Questions: Is the 30# felt for the floor and urethane for the loft floor going to be enough insulation for such a cold climate (western ny state)? By "urethane" are they talking spray foam, or can we use foam sheets? And for the roof, it sounds like they're saying we can only use felt if we put up shingles. We're going with a metal roof, so can we use felt with that? Will it be heavy enough insulation? Or should we go with MtnDon's proposal of blueboard-in-OSB sandwich? The felt would be much less expensive, and money is always on our minds, so if we can use it rather than the blue board we would really like to do so. Also, what the heck is cdx?

# Posted: 10 Sep 2012 15:10

The felt probably has no insulation value but is intended as a vapor barrier. Urethane insulation can be in sheets or spray foam and has an excellent R value of about 7/inch. CDX is plywood having low-grade facings of C and D grade that is rated for exterior use.
I am not familiar with the insulation requirements of western New York so I don't know what the R value for flooring and roofing needs to be. Probably more than 2 inches of foam, though.

# Posted: 10 Sep 2012 16:09

The felt paper is only for a moisture barrier. I used R19 under the floor and held it up with 1/2" rigid foam board. I then covered it with wire mesh to keep the critters out. The floor is nice and warm. Where your cabin will be the more isulation the better.

I checked into spray foam insulation. The guy wanted $7200.00 to do the cabin. Needless to say fiberglass roll insulation from Lowes worked just fine.

# Posted: 10 Sep 2012 18:04

MTNdon's suggestion for metal roof is the best way ,the intention is for moisture build up under the metal roofing and then causing problems, not insulation for heating purpose. Cooking, showering etc.etc.. inside the cabin causes moisture..

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