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Basment Remodel - Question About Subfloor

886 Views 1 Reply 1 Participant Last post by  b-boy

I'm remodeling my basement. The house is about 120 yrs. old. The basement has really thick cement walls, the floor is in good condition, and there is virtually no water infiltration into the house.

The only water I've seen came from a sewer backup during a 50-yr storm. We got 6.5 inches in a little over an hour. Even then I got about 1/2 inch in the basement. That came in through a floor drain that's tied into the main sewer line. The sewers were overwhelmed and sewage backed up into most of the older homes in the area. I've fixed this problem using a plug and some backwater valves in the basement bathroom. Hopefully this holds up during the next monsoon.

I've been reading about different methods for applying insulation and vapor barrier to the basement. I'd settled on 2" XPS on the walls, 6 mil plastic on the floor with 2x4 PT sleepers insulated with 1" XPS covered by 3/4" plywood. I did this in my old house and it worked well. It was an incredible amount of work though. Especially since the floor was so uneven.

It sounds like an easier option is 6 mil plastic, 1" XPS, and 3/4" plywood sandwiched together. I would use a powder actuated nailer to drive 3" nails with washers into the concrete.

However, my floor is sloped to drain into a corner drain. It's fairly level in most spots, but there is a 3"-4" drop from the highest point to the lowest point. This is over ~25 ft. It's not a gradual drop in some spots. The dip is noticeable. Especially close to the drain.

When I did sleepers, I was able to level them to account for the floor slope. How do I accomplish this with the option mentioned above?
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As a follow-up, assuming I use the 6 mil plastic, 1" XPS, 3/4" plywood sandwich, what is the recommended method of putting up walls around the perimeter of the basement? There will be 2" foam attached to the walls, but do I put them on top of the subfloor, or build the walls first - then butt the subfloor up against them?

I'm assuming I'd want to put the walls on top of the subfloor since they would create a break in the vapor barrier the other way, but I've seen it done both ways.
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