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jovol
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# Posted: 29 Nov 2021 13:54
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Hey all, I've just finished setting up and leveling a park model cabin on my property near Asheville NC. Before moving it here, I ripped out all the floor insulation as it was 20 years old, sagging, and I could tell rodents had been in it. I now have a blank slate: 2x6 joists 16" oc. It gets pretty cold in this part of NC, typically 15-25F November-April. I'll be heating with a vermont castings aspen wood stove.
I'm pretty overwhelmed with all the options for insulation. Fiberglass, rockwool, EPS/XPS, etc. Do you have a good recommendation? I will be framing out a wooden skirt wall and putting some kind of bubble foil on the inside of that to prevent my pipes from freezing. I don't want rodents, don't want ant damage in a couple years, so.... what's the call?
Thanks for your help,
John
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travellerw
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# Posted: 29 Nov 2021 14:04
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I have heard people say that mice won't nest in Rockwool. However, our mice must not have got the memo as they will happily nest in it up here.
This is the method I settled on. It keeps all the insulation on the interior and utilizes EPS which mice like less.
https://www.youtube.com/watch?v=zWAt0fB_hSA
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gcrank1
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# Posted: 29 Nov 2021 14:17
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Sounds like you have good access underneath?
Spray foam (hire someone?) seems great, tho at a price.
On our old build ('83-'84) we used blue DOW styro between the floor joists right at flush to the top; the subfloor 3/4" cdx went right over it. The styro sat on furring strips. Id do it again with exposed joists topside. The underside was never covered and we had no issues with vermin or insects under there.
It could be done from below tho a bit awkward. The sheets could cut to size and be pressed up in place and temp held up with a nail here & there, then fit in furring strips. A nail gun would be nice for that, I think.
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jovol
Member
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# Posted: 29 Nov 2021 15:28
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I have good access underneath, relatively easy to work on my back with about 18-24" of headroom.
The interior is already finished (the cabin is ~20 years old), so laying down foam/osb panels on the interior is a no-go. Looking for recommendations on installations from underneath.
I've read ants like to bore into EPS/XPS. Is this a legitimate concern if I put the foam boards inbetween the joists and leave them exposed?
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travellerw
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# Posted: 29 Nov 2021 15:48 - Edited by: travellerw
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Quoting: jovol I've read ants like to bore into EPS/XPS. Is this a legitimate concern if I put the foam boards inbetween the joists and leave them exposed?
I think it might be regional. Up here EPS is used around foundations all the time at ground level. If ants were boring into it, I don't think it would be used.
GC's suggestion of pushing the foam up is probably your best option for off the shelf. Tedious as you need to cut each panel unless your cabin is built better than most. You could cut each one a little smaller, use nails to hold it up, then spray foam the gap. However, that could get expensive in canned foam.
I also think spray foam is an excellent option if you can swallow the price.
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gcrank1
Member
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# Posted: 29 Nov 2021 17:07
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I measured each opening between my joists and cut 4x8' sheets with a very Sharp and Thin utility knife. (we used 1" styro, for 2" Id be tempted to dbl up 1" maybe) Be aware that the styro cuts much 'cleaner' on direction than the other, like a 'grain'. The wrong way pulls fingers of styro on the stroke.
Having a long drywall square/straightedge was nice! Did take two of us, my wife held the far end of the s-edge so it didnt slip on me.
As I recall (it was decades ago) I took to measuring each 8' run between the joists at 3 places to mot be surprised when a piece didnt fit. It really went pretty well, at least the foam is lighter than most buildimg materials 
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jovol
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# Posted: 29 Nov 2021 18:45
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I'm definitely attracted to the rigid foam direction. Fella on craigslist here sells 2"x4'x8' sheets for $20, would need 12-13 sheets so only about $260. Plus a couple cans of gap filling foam and I'm in about $300 with R10 floors. Rockwool R15 would run me about $400 just for the insulation, not sure exactly what else I'd need with that route, but something should probably cover the rockwool? Hell I could double up the foam boards and get ~R20 for $520.
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spencerin
Member
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# Posted: 29 Nov 2021 18:50
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Spray foam is probably the best choice. It's the easiest, too, but the most expensive. After that, I'd say it's a tie between rigid foam board and fiberglass batt insulation. If you want to keep pests out, you'll need to seal the bottom tight with plywood.....the additional cost of which might make these options comparable to spray foam. Good thing is you appear to have enough headroom to work with. Mice are generally known to avoid spray foam but chew up the other types.
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jovol
Member
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# Posted: 29 Nov 2021 19:15
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Is there a good reason not to install the rigid foam boards screwed into the bottom of the joists? That would make it very easy to tape/seal all the seams between boards, and nix the cutting process.
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gcrank1
Member
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# Posted: 29 Nov 2021 21:25
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To my thinking that would leave an inviting cavity for critters. 
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travellerw
Member
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# Posted: 29 Nov 2021 22:17
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Quoting: gcrank1 To my thinking that would leave an inviting cavity for critters.
Yup..I would think a mouse disco tech. Them mice be dancin and sewing dresses for the ball!
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jovol
Member
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# Posted: 29 Nov 2021 22:55
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Alright say I did the 2" foam, then sealed the underside with plywood, would that 4" cavity between the foam and plywood also be a disco ball for rodents?
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gcrank1
Member
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# Posted: 30 Nov 2021 00:08
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Ime rodents are ocd about finding out what is on the other side of a surface blocking them. The thinner the material the quicker they gnaw thru it. Once a cavity is found it becomes theirs.
Iirc someone mentioned using metal soffit material?
All I know is that the floor we did with the 1" flush with the joist tops and directly under the subfloor 3/4" cdx, fully exposed beneath did not have any issues. Thru the years I had occasion to crawl under and I was curious....saw only spider webs. We did have mice that tunneled up and thru the butt seams of the same styro outside of the wall sheathing and eventually made their way inside (even tho I had taken care to build tightly)It took some years, they were persistent....
Ymmv
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Brettny
Member
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# Posted: 30 Nov 2021 05:36
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Ants will nest into XPS, they did it in my house but the whole place was a carpenter ants nest.
If your going ridgid foam direction put it right up against the sub floor and use caned spray foam at all the edges. It really holds it in place well and seals things nearly like spray foam.
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