insulating concrete floor for radiant ht
I am installing radiant heat in the concrete basement floor of a new building. The building has a walk out basement. The insulation, tubing, and forms are set to pour the floor on Tuesday morning. I have insulated under the floor and around the perimeter with 2″ rigid foam insulation. However, there is a problem with insulating the floor on the walk out basement wall. My concrete contractor wants to pour the concrete for the floor directly onto the frost wall on that end of the building. Structurally this is the right answer, but this also connects the floor thermally into the concrete of the frost walls which are not insulated and the rest of the foundation.
The walk out end wall will be framed on the floor, so a good foundation (without compression) is necessary.
Is there a material that I can use to insulate between the top of the frost wall and the floor which will support the load for the gable end wall on a single story building and not compress over time?
Thanks for your help.
Allen
Replies
There are a number of options. One is to cover the outside of the stem wall with dampproofing, in the normal way, insulate with XPS sheet, then backfill to grade. If any part of the XPS will be exposed above grade, it should first be covered with a protective barrier (e.g., flashing) before backfilling.
If the stem walls are thick enough, you can reserve enough width to frame the wall, and put the slab on top of XPS sheet on the rest. For example, if the stem wall is 8" thick, and you're going to frame a 2x4 wall, you've got 3-1/2" for the wall, and 4-1/2" for the slab.
If you don't have enough width in the wall, you can create a thermal break by partially covering the stem wall with insulation, leaving enough concrete to bear the load.
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-Steve
thanks,
we are using the last option you mentioned. i.e. covering most of the frost wall with insulation, and leaving enough concrete to concrete contact to support the load.
we discussed the option that you presented where the floor stops short and the wooden wall is built on the frost wall. My contractor felt that this would cause problems with the wood (below the top of the concrete) because of trapped moisture from the concrete sweating.
thanks again for your helpful (and timely) suggestions.
Allen
"My contractor felt that this would cause problems with the wood (below the top of the concrete) because of trapped moisture from the concrete sweating."
Yes, you'd need to use a polyethylene vapor barrier between the wood and the concrete in that case. (Obviously, my quick sketches left out a lot of the details...)
-Steve
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