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TF1
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# Posted: 20 Jan 2025 10:16am
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I'm finalizing my under cabin spray foam quote for a spring install and was looking for feedback on sealing it up with either 1/2 OSB or plywood. Difference is currently around $20 a sheet ($480 total approx diff.). Cabin is 3ft above grade.
Any other recommendation on the install? Seal any corners? Tape seams?
Leaning towards plywood.
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gcrank1
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# Posted: 20 Jan 2025 11:17am
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OSB is mighty heavy working from under
Or, in other words, imo NO WAY
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Brettny
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# Posted: 20 Jan 2025 02:52pm
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I wouldnt skirt it at all. Spray foam the bottom of the sub floor and put the plywood on the bottom of the floor joists. I also dont believe they make a OSB that can be used as skirting. No amount of ground heat will make for a warm floor when it's cold out.
I have 4in polyiso under my subfloor with no skirting. My floors are really warm even at last nights 5*f.
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gcrank1
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# Posted: 20 Jan 2025 03:10pm
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Hmmm, I didn't think it was about skirting but up on the joists.
Fwiw, on my '83-'84 build I put blue DOW styro between the joists before decking. It had no barrier exposed to ground. Afaik (and Id look under there from time to time) nothing dug at it or Id have seen blue bits. That doesn't mean it wouldn't be a bad idea.
Think Ive heard of someone using the alum soffit sheeting to keep critters from going at it.
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ICC
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# Posted: 20 Jan 2025 08:34pm - Edited by: ICC
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Quoting: TF1 Leaning towards plywood.
I used CDX plywood; 3/8". Installed almost 20 years ago and never have had any issues. It is installed with the same panel spacing as one would use for subflooring or wall sheathing. No cracks or voids anywhere. To make it easier, in places I installed extra blocking as nailing surfaces.
In the areas where plumbing or wiring was run, the panels were secured with screws rather than nails, just in case access would be needed at some future time. Some of those are installed lapped over the nailed-in sheets. Easier to find them.
As far as skirting goes, here in the western mountains I would not want to be without metal skirting. That is because of wildfires, high winds and blowing embers. Wildfire embers are different from campfire embers. They can be small but can also be chunks as big as your fist, or larger. Metal skirting will keep those from being blown under the cabin.
Skirting does require ventilation and using screening with openings small enough to prevent small embers from blowing through. 1 sq ft per 150 sq ft of floor area, minimum. That is 1 sq ft of open vent space; the mesh cuts down the effective vent space. I think I used almost double the recommendation. Not seasonally adjusted.
FWIW, I also applied aluminum flashing material underneath the cantilevered undersides and used fire-resistant siding, trim, soffits, fascia, etc. Metal roof. The skirting is ribbed roofing panels cut short to allow the ribs to be vertical. PT 2x4 framing between the piers, not quite touching the ground level.
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TF1
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# Posted: 21 Jan 2025 10:35am
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Thanks. For clarification, the plywood would be attached to the bottom of the joists. Main concern was protecting the spray foam from embers etc. I've seen some documentation online stating the foam includes a fire retardant, but then other posts claiming the foam needs to be covered.
I won't be doing any skirting for the time being. Too many other projects.... appreciate the reply's.
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spencerin
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# Posted: 21 Jan 2025 09:01pm
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Plywood
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