Insulating slab on grade garage floor...

Old 05-21-08, 03:03 PM
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Insulating slab on grade garage floor...

I am building a 24'x24' detached garage/workshop with the intent of using it year around up in Calgary, Alberta. Winter here can be long and cold, so I would like to minimize heat loss thru the concrete slab as much as possible.

The garage floor will be slab on grade, and I would like to add insulation and a vapor barrier during construction ie. under the concrete. I have read some material regarding the use of rigid foam insulation under a concrete floor, but would like someone to more clearly explain the how&what is involved.

I have spoken to a contractor who told me that the vapour barrier (poly) should be under the insulation, but this seems contrary to other info I have read....

Any input would be much appreciated as I am total newbie to this homeowner/addition-builder stuff!

Brian up in the great white north
Old 05-22-08, 08:34 AM
Join Date: Nov 2001
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The slab of my shop is insulated from the ground and footers in order to use radiant hydronic heat in the slab. I used rigid foam insulation without any other vapor barrier, following the construction plans from the manufacturer of the radiant heat product. The floor is finished with epoxy. In three years, I have had no problems from moisture intrusion with this method. From my experience, I see no reason to use more of a vapor barrier than is provided by the rigid foam insulation.

If you wanted to use a polyethylene barrier, it would seem to me that it would be more beneficial to use it beneath the rigid foam as it would have no seams.

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