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Sleepers over concrete

I'm looking for framing advice. I'm going to create a dining room in teh back of my oversized garage. The garage floor is a concrete slab over a crawl space with a dirt floor. The crawl space is dry. In order to bring the garage floor up a step to match the floor of the house, I plan to construct 2x8 sleepers to support the subfloor of the new space.

Some of the questions I have are around the space between the concrete and the subfloor. Should I lay a moisture barrier on the concrete floor, under the sleepers? And is spray foam insulation the best to use against that concrete to prevent a chill from rising up through the subfloor? If using spray foam, should the moisture barrier then go between the sleepers and subfloor- or is the spray foam effectify a moisture barrier (except where the sleeper touchess the concerete? So does that mean the sleepers should be raised over the concrete to spray foam is between? Or do I use moisture resistance lumber on the concrete, spray foam, and call it a day?

I keep circling here- if you were framing a floor over a concrete slab, can anyone suggest the best order of materials?


A. Spruce
Re: Sleepers over concrete

Where wood meets concrete it needs to be pressure treated material. What I would recommend instead is to use Trex, or similar engineered lumber as "feet" under your joists, you won't have any issues of moisture transfer or rot this way, should it ever get damp under there.

I would leave air space between the cement floor and the framed floor. The reason being, if water ever does get in there, you want it to be able to get back out and to dry out. The air space will allow for this. No need for a moisture barrier with this set up.

Personally, I'd use fiberglass insulation. It is cheaper and easier to use.

Re: Sleepers over concrete

Thanks for the advice. I like that idea- and in fact I have a bunch of leftover trex pieces leftover from a deck project last summer.

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