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WILL1E
Moderator
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# Posted: 25 Aug 2025 03:45pm
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Me again! Another project on the short list for this fall is to finally insulate my cabin floor on my elevated cabin. I know I had this discussion at some point on here, but my search skills are lacking a bit.
If i recall, my best bet was to get 2" pink foam and cut it to fit between the joist and push it tight up to the subfloor. I believe someone suggested tacking it in place using long finish nails using a finish nailer shooting it at an angle through the foam and into the joist (not the subfloor). Then i believe it was suggested to come back and seal the edges of the foam with spray foam to keep anything from getting behind it as well as to further lock the foam in place.
Does this sound accurate?
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Brettny
Member
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# Posted: 25 Aug 2025 05:02pm
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I did 4in polyiso under my floor. Made a stand of block with a hole in it for my finish nail gun. I set it to not shoot through 3/4 sub floor. I just pushed the insulation into the nail heads. I also used caned foam for all the edges of the foam. This floor is warmer than my houses floor with basement and Insulated rim joist.
I'm not going to skirt my cabin either. Dosnt need it.
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jsahara24
Member
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# Posted: 26 Aug 2025 09:04am
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Yes it sounds like a good plan to me, other option would be spray foam but lots of $$$$....
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gcrank1
Member
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# Posted: 26 Aug 2025 10:40am - Edited by: gcrank1
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Ime, cut & fit rigid styro is labor intensive/futzy but clean work (though not if you saw the styro!....those little bits of styro are easier not created than collected)
So, how to cut thick styro well; ie, straight and deep? I know I had enough trouble cut & fitting 1" (thin, Sharp knife; and note that styro has a 'grain', it cuts cleaner one way than the other).
Btw, dont buy new styro, find someplace that has surplus or reclaimed; after all it doesnt need to be pretty.
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jsahara24
Member
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# Posted: 26 Aug 2025 01:12pm
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Quoting: gcrank1 how to cut thick styro wel; ie, straight and deep?
I insulated my guest shed with 3" rigid foam board. The guy I bought it from advised a "hot knife". I used a circular saw and sawzall which definitely made a mess....
But I figured since i was foaming the edges it didn't need to be perfect....But its worth looking into, I see one at Harbor freight for 30$.
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Brettny
Member
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# Posted: 26 Aug 2025 03:15pm
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I used a table saw outside to cut my poly iso. Didnt cut all the way though. Just snap and finish cut with a knife. My pony iso has a fiberglass coating on both sides so really itchy and you dont want to breath it. Table saw was the fastest and least laborious way.
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