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Jim McC 06-19-2013 01:11 AM

Concrete floor in 3 season porch
We are looking into building a 3 season porch in S/E Wisconsin, and are considering a concrete slab floor. Is it worth putting in 2 layers of 2" rigid foam under the slab, instead of just 1 layer? The porch will be about 12' X 19', with the floor about 16" above grade. Thanks.

Windows on Wash 06-19-2013 07:08 AM

For an extra 7 sheets of foam, I would go with 2" in total or just a 2" thick piece.

Gary in WA 06-19-2013 02:29 PM

You need to understand slab heat loss in more detail. Most of the loss is at the perimeter which is why code (minimum) requires it there (4' in) for your location, Zone 6;

Normal slabs will mirror the air/surface temps, your slab is elevated which helps thermally, a little- depending on the capillarity of the soil;

You could get spring/summer condensation on the slab due to the winter lag temperatures, so; great you will insulate it all;

Though 4" is too much for the middle areas, it is perimeter you should be really concerned with;


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