Insulating existing garage floor

[concisedesign]

I am converting a garage floor into a bedroom in central MA.

The uninsulated slab is 8" below finished wood floor. Am going to carpet the new floor. Am I best off with 2x8 sleepers and rockwool insulation or just 2" rigid foam with 3/4" plywood tapconned into slab?
The HO is fine with having a step at the threshold.

I understand that IECC calls for more than R10 in Zone 5, but wondering
if the overall assembly would be better with rigid board.

Thanks,

CD

[Happy Home]

http://www.greenbuildingadvisor.com/...oncrete-garage

[worthy]

The foam provides a complete capillary break and, by eliminating thermal bridging of the sleepers, provides a higher effective R Value for the floor than by using sleepers.

[NW Architect]

6" foam, 2x4's on flat, 1/2" plywood. Flat, aligned, warm, and easy.

[dgbldr]

6" foam, 2x4's on flat, 1/2" plywood. Flat, aligned, warm, and easy.

And crush the foam as soon as you bring in a heavy piece of furniture :)

[Dutchman]

If 8" is the build-up....6" foam, 2" concrete with radiant.

[NW Architect]

#5, well, you have to get a proper density of foam.
#6, I like that better than the wood assembly. And since there's probably a slope to the garage floor, concrete topping can compensate. Although I might go for 2-1/2" min. on the concrete

[concisedesign]

this is a lower end rental unit, so I think I'm going to skip the 2" concrete topping with radiant.

Does double plywood need to be tapconned to floor, or can it float? Do sleepers need to be tapconned if used with single plywood system?

[Dutchman]

Does skipping the radiant help the budget?

Any wood assembly is going to be a bit hollow sounding.

So, from bottom up: 6 mil poly, foam, sleepers @ 12" o.c., 3/4" ply. Let the sleepers and ply float on the foam.

[worthy]

I fail to see the purpose of the sleepers or of the poly, which will just trap moisture between the concrete and the poly; nor the need for R30.

An alternative approach designed for a monolithic slab is in Lstibruek's Builder's Guide to Cold Climates p. 107: dimpled plastic sheet (such as Delta FL) XPS with no facers and 3/4" t&g plywood not fastened "so that gas barrier/air barrier is not compromised". Also, Lstiburek notes that in this type of construction insulation should be limited so that the slab can dry upwards.

Elsewhere Lstiburek shows a layering Figure 3--of XPS, building paper and wood subfloor.