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Small Cabin Forum / Cabin Construction / Insulation under cabin
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# Posted: 19 Oct 2015 17:02

Anyone ever try Mine Foam?

Its basically a bulk container of Great Stuff foam with an 11 foot applicator hose. We had it by the pallet when I worked at a lead smelter. Very tough stuff when cured, I know of a couple room air conditioners stuffed into oversize holes and held in place with just mine foam.


Its about $215 for the 180 board feet kit (1 inch thick)

I know if rodents tried to chew through it, they would wind up with broken teeth. LOL.


# Posted: 19 Oct 2015 17:22

Perhaps I missed it when I read the web page and data sheets, but it seems to be a sealant rather than an insulator. I don't see any R-value claims for it.

# Posted: 20 Oct 2015 12:29

I insulated my floor during construction. I nailed a 1"x 4" to the bottom of the joists. Cut and installed some scrap plywood to fill in the bottom of the bays. We then insulated with 2 layers of R12 fiberglass insulation. I like to use 2 layers of r12 instead of 1 layer of r 24 because I like to cover of where the insulation batts meet. As MTN Don mentioned you want to have this clad to weather asap to keep the insulation dry.

# Posted: 9 Feb 2019 14:42


Hi - So if I understand what you did - rather than playwood skirting around the underside of your cabin, you instead used R5 Insulation panels and put two layers with spacing in between? How did you secure them and keep the 8inches betwent them with wooden block?

What about rodents digging under squeezing around same and living under camp?

Is your floor of camp insulated?

I have a cabin in Western Maine on a lake and have either block in and or insulate floor - concerned about rodents and avoiding moisture and rot etc.

Let me know,

Thanks much,


# Posted: 12 Sep 2021 09:16

Jim in NB
Jim, can you tell me how insulating the skirting has helped. I am in northern Ontario and have a similar issue. Dan

# Posted: 5 Nov 2021 02:15

You sure don't want to insulate with fiberglass before the cabin/floor is dried in. Putting insulation between the joists, and then covering the bottom of the joists with plywood or OSB requires working from underneath, which isn't always so easy (as in try laying on your back, holding a piece of 4x8 ply against the bottom of the joists while you screw or nail up). There should not be any air space between the floor and the insulation beneath. Air, alone, is a poor insulator. In my experience with batt insulation, anything nailed or stapled to the bottom of the joists does not keep the insulation tight to the subfloor.

I find it easier to work from above. Following is a method used by log builders in Alaska, endorsed by the Alaska Housing Finance Corporation (Alaska Log Building Construction Guide, 1999). I've improved on it slightly, I think.

After joists are in place, nail a layer of OSB on top, marking joist locations with a chalk line. Then lay XPS foam (the blue or pink stuff) in 2'x8' x 1.5" panels at right angles to the joists, separating each run with a 2x2 screwed into the joist crossings. A second layer of foam insulation is added perpendicular to the first, again separated by 2x2s, screwed at each wood-to-wood crossing. Keep a rim of 2x4(s) or 2x6(s) on the flat all around the platform perimeter, flush with the top surface of insulation. This wood will bear the weight of the walls/logs down to the joists/rim below. Finally nail your 3/4" T&G plywood on top of this assembly, screwing down into the 2x2s, and into the 2x lumber around the perimeter.

There is no measuring and cutting to fit insulation to joist spaces. You've nailed and screwed down instead of from your back, reaching up. Gravity works to hold materials down, and tight, as you build. You have eliminated thermal bridging through the joists. The top T&G ply is fully supported by high-density foam and 2x2s. Because it's T&G, there is no need to worry about the dog's water dish tipping or mop water reaching the insulation (you can add a bead of caulk to the T&G seam when installing, if you wish). If it rains during the build, that's OK. The insulation will not be compromised, and any moisture will dry outward.

Yes, the platform deck is raised up a few inches, but the platform can "start" anywhere. There just has to be solid wood support from heavy wall logs (or wall framing) down to the joists spanning the beams.

As others have noted, closing in the space beneath the platform with any kind of material between the perimeter piers reduces airflow, and will make the floor warmer. Between that, and 3 inches of XPS rigid foam, you'll have yourself a warmer floor, and one that was quite a bit easier and faster to build.

# Posted: 7 May 2023 11:46

This is osb and not plywood. Should be pressure treated being close proximity to gound and moisture to prevent mold, fungas and rot.

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