Insulation Under Floor

4 years ago

I'm in the process of removing my sunken floor in a living room. The plywood below the joists is sitting on 2x4's on top of a dirt floor, but it's not in contact with the new floor joists. One of the walls is an outside wall, but the others are inside walls. Just wondering if i should be putting insulation between the joists and what type or if I could get away with no insulation. The room was not cold in the winter before but I'd like to do it right.

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Comments (7)

PRO
G & S Floor Service
4 years ago
Spray foam will be best. You want it tight to avoid condensation.
kudzu9
4 years ago
"...2x4's on top of a dirt floor." Are these 2x4's pressure treated? And if they are not connected to some type of concrete footer, what will prevent their sinking into dirt in the future and causing the floor to sag?
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mojavemaria
4 years ago
Yes subfloors should be insulated. if you are in an area that requires a vapor barrior it should be on the top side facing room. Spray foam is its own vapor barrier and it makes an airtight seal but it is expensive.
millworkman
4 years ago
Is there a vapor barrier installed over the dirt?
Chris Wharton
Original Author
4 years ago
No vapour barrier on the dirt. Never had issues with moisture in there, we live in an arid area.
Chris Wharton
Original Author
4 years ago
@kudzu9 the plywood that you see below the joists is the old floor. Not attached whatsoever to the new joists or subfloor. Plus it’s been there 30 years and no problems.
kudzu9
4 years ago
Chris-

Sounds ok. I just couldn't tell from the description whether there was any new stuff installed in contact with dirt, or old stuff directly supporting anything new.