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Community and Q&A

Framed floor over concrete slab

user-1045979 | Posted in Green Building Techniques on

I’m working on building a new home near Seattle (4C) that will be, for the most, a concrete slab on grade finish floor. In the bedrooms, though, I’d like to install carpet and I’m trying to come up with the best assembly to do so.

The slab will have 2-4″ of rigid insulation (depending on budget) and a vapor barrier under the slab.

I was thinking of laying (non-pt) 2x4s on edge @ 24″ o.c. with a layer of 3/4″ plywood over that, then installing the carpet on the plywood.
To my thinking the concrete should be warm and dry and the plenum shouldn’t be functionally different than a typical floor (except with concrete instead of gwb on the bottom).

I realize I could probably leave the 2x’s flat but if there’s going to be a step up from the concrete 4+” feels like a real step while less than 2″ seem like an awkward tripping hazard.

Further, (and this might be far-fetched or not well thought through) would it make sense to run plumbing through this raised floor rather than through the concrete where it would be accessible?

I’d love thoughts on this. Looking online I can mostly only find solutions for adding floors over garage slabs that have no vapor barrier or insulation.

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  1. Expert Member

    Is there some reason you aren't just installing the carpet on the slab?

    A change in levels between rooms causes a lot of complications. Have you considered framing the floor flush with the slab either by dropping the slab at the bedrooms, or doing away with the slab altogether in those areas and framing the floor directly on the foam?

  2. walta100 | | #2

    Installing the carpet and pad directly on the concrete is the standard operating procedure.


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