insulating floor of mudroom before closing it off
I’m building 5′ by 8′ mudroom addition where there previously had been a dilapidated porch-like structure. I’ve poured the foundation and secured the sill. The concrete foundation is about 5 inches above soil, then 6 x 6 sill. I will be framing the floor with 2x 6. I’m stuck with these dimensions because of grade etc. This “crawl space” is NOT connected the the main house’s crawl space and will be 100% inaccessible once the subfloor goes down. Also, foundation is non vented.
Anyway- the plan is to-
air seal between sill and foundation with canned spray foam, then apply rigid foam around perimeter in a cut and cobble fashion.. The goal is to fully air seal the perimeter
then…..6 mil plastic on soil weighted down with gravel and rocks
then mineral wool between floor joists with some sort of cleats or pipe strap to keep it from drooping down over time.
What am I getting wrong? I don’t want to make it more complicated than it needs to be. It’s a 150 year old house and this is a tiny addition. But I also don’t want to create a tropical eco system under my floor.
Thanks in advance.
Replies
If I read this right...
Sounds like a great recipe for a mushroom farm and there are lots of fungi that like wood. Seriously, though, I can't imagine you could exclude enough moisture to make that work, In my area the termites would also party. Why not pour a small slab?
I believe code requires at least 18" between the bottom of floor joists and grade for a crawl space. Sounds like your plan only achieves 11".
I agree with old hand that a slab on grade would be more appropriate for your situation. Specifiacally, I'd recommend to insulate foundation wall and at least 2' inside of exterior wall at perimeter, gravel fill, vapor barrier (which can be achieved with closed cell foam thereby achieving insulation at the same time) then pour your 4" slab.
Testing, 1, 2, 3. Does posting work on this thread?
Thanks for the responses. They are much appreciated. Someone else suggested a slab as well. I did a little research and it makes perfect sense....hindsight being 20/20 and all of that. It would have to be a retrofit due to the fact that the foundation is already in place. And the sill is bolted on etc. So to pour concrete would essentially be more of an infill situation rather than an actual foundation.
Like I said I'm considering it. I kind of wish the mason had steered me in this direction initially. That's sort of the reason I hired out for the foundation pour.
Incidentally, Mineral wool is an inorganic material meaning the mold problem usually associated with fiberglass in crawl spaces would not be an issue....at least in theory and according to the manufacturers literature. My thought was that by air sealing perimeter, laying plastic and gravel and insulating joist bays with inorganic material, I'd be building a pretty dry assembly.
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Fiberglass is inorganic as well.