Wood floor over concrete slab

**Chris McIntyre** · 09-04-2012, 04:54 PM

I have seen this done many times and many different ways, I would like any opinions, reference material and/or codes on how it should be done.

Converting a porch to heated space. Porch slab 3 to 6 inches lower than the house, sleepers installed with subfloor so the new floor is the same height as the existing house floor.

Does a space this small have to be ventilated? Are there any other options short of pouring 6 inches of concrete over an existing slab?

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**Raymond Wand** · 09-04-2012, 05:19 PM

Why not install several layers of rigid insulation board, overlap seams and tape with tyvek tape to bring the level up and top it with your flooring?

That way the floor will be well insulated, warm and seal out any moisture vapour from coming up through concrete, won't require venting, and would be cost effective.

BSI-059: Slab Happy — Building Science Information

**John Kogel** · 09-04-2012, 06:34 PM

Agreed, foamboard is miracle stuff. A little pricey, but worth it.

**wayne soper** · 09-05-2012, 08:22 AM

starting with a full plastic vapor barrier

Garry Blankenship · 09-05-2012, 08:40 AM

Recently did this building a bungalow for my Mom in my shop. Shooting down sleepers to get the flooring off the concrete is a lot of work. Both Lowes and Home Depot have a product for this, ( different mfgs. ). Both products are made in 2' x 2' squares, T & G edges that fit together tightly and a particle board top sandwiched to a moisture resistent bottom. One mfg. has a foam bottom and the one I used has a durable high density poly bottom that looks like athletic shoe bottoms for artificial turf. I chose the plastic bottom because it would allow moisture that might wick up through the concrete to travel and better dissapate. Easy install and you can frame on top of the product. The insulation "R" factor is not good, but all else is great. If you do not find these products, P.M. me and I'll look it up.

**Chris McIntyre** · 09-06-2012, 12:16 PM

AHJ said they didn't design just approved or disapproved what was done. So, what was agreed upon and approved was: concrete was sealed PT sleepers installed space between sleepers filled with foam board.
Thanks to Marcus and all that posted.

**Jim Starkey** · 09-07-2012, 07:59 AM

I call this a scredded slab or is it scretted slab? anyway its not very desirable as this area when finished out is not accessible for inspection, can harbor termites, rats, mice etc. I have a pretty long winded canned statement for this type of slab that I use when a whole house is done this way or a large area. There are houses in my area that were built this way for a very short time in the early 60's late 50s when they went from pier and beam to slab foundations. They did this to make the slab seem like a pier and beam with wood floors with the hollow sound everyone was use to but they quickly abandoned it due to the problems listed above. I would at the very least make a note of it and mention its not accessible for inspection and verbally tell them the problems with pests.

**Mark Reinmiller** · 09-07-2012, 10:20 AM

Chris,
I can't give you a reference for this off the top of my head, but ventilation is probably not that important if the slab is somewhat elevated and drainage is good. I think putting a moisture barrier over the slab would be advisable. I converted my garage to an office about two years ago. To deal with the sloped floor and to have a warm floor I put down sleepers and filled the area between them with rigid foam. I did not use a moisture barrier because I was confident that the slab was dry. It worked out well.

**John Kogel** · 09-07-2012, 12:39 PM

A vapor retarder, such as good old tar paper, building paper, is good to lay in strips under the wood. That will stop the wood from drawing moisture from the concrete. In my climate, poly on concrete would trap and hold moisture.

Jim, I think the word you seek is "screeded', the concrete for the slab was leveled with a screed, usually just a long 2 X 4.

**Jim Starkey** · 09-07-2012, 03:30 PM

Originally Posted by John Kogel

A vapor retarder, such as good old tar paper, building paper, is good to lay in strips under the wood. That will stop the wood from drawing moisture from the concrete. In my climate, poly on concrete would trap and hold moisture.

Jim, I think the word you seek is "screeded', the concrete for the slab was leveled with a screed, usually just a long 2 X 4.

John, no I know about that I'm talking about the practice of lying 2x4's on their edge on top of a slab foundation then lying sub flooring over that then wood floors which was a practice done here in my area back in the late 50's early 60s. They ran duct work and other stuff in the void but mainly did it so the house had the Pier and Beam feel everyone was use to when they transitioned over to slab foundations from pier and beam foundations. I don't see to many of them but there are neighborhoods full of them from that period. Its a heaven for termites, mice, roaches etc and no way to visually inspect it. Not a huge deal but something you want to mention in your report that its not accessible for inspection when you see this type of built up area with a slab under it with no access. I think this may have been something that is unique to my area here in Texas.