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How to insulate an above-grade interior foundation wall and curb?

We have a concrete slab foundation. Plan to lay Delta-FL down on the floor with plywood and hardwood flooring on top. Problem is that there is an above grade concrete curb surrounding the floor that protrudes five inches above and about 2 to 3 inches out from the drywall on the walls.

There is also one wall where the concrete foundation wall is about 3 feet above the floor (above grade with a crawl space on the other side), Exterior moisture intrusion is not a problem.

We need to insulate the curb and wall but don't want to create a mold problem due to thermal differential. Also don't want the curb protruding any further into the room than necessary. Thought about rigid foam, but that requires fire proofing outer finish. Dry wall over the foam would be a bit delicate for a curb. Not sure if putting the Delta Fl over the curb and wall would be a good idea or not.

Any ideas?

Asked by Ken Messenger
Posted Sun, 12/22/2013 - 19:17
Edited Mon, 12/23/2013 - 07:29

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Ken,
I don't think you have any choice: you have to insulate this concrete wall on the interior, and rigid foam is the logical insulation to use.

I hope that you have a continuous layer of horizontal rigid foam under you slab. If you don't, you should consider installing a layer of rigid foam above the slab before proceeding with the Delta-FL and plywood.

If you have horizontal rigid foam under your slab, the best installation would require the slab to be cut back 2 inches or 4 inches at the perimeter, so that you could install some vertical rigid foam at the perimeter of the slab the connects the sub-slab foam with the foam that you are about to install on the interior of the concrete curb.

After you have insulated the concrete curb with 3 or 4 inches of rigid foam, you can either install some thin framing, or just glue some drywall to the foam. Another option is to install vertical plywood on the interior side of the curb foam, fastened with TapCons through the foam to the concrete, and then a layer of drywall.

Answered by Martin Holladay, GBA Advisor
Posted Mon, 12/23/2013 - 07:00

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