OK Folks, what is likely needed vs ideal? I ask because my choices are $30 for R10 vs $18 for R5 a sheet (roughly) when comparing Owens Corning FOAMULAR 150 at HD -- look at the Owens Corning site this is one of the choices listed for under slabs.
Thoughts?
Any amount is better than nothing. Climate zones 4, 5 & 6 are recommended to have R10 under a slab for a habitable space with an additional R5 for slabs with heating built into the slab (radiant).
Not much difference when looking at a small area.
BTW, the greater the temperature differential between the interior space and the ground under the slab, the faster the heat transfer.
So better to spend the money on the R10 then :( Of course I knew that but was hoping maybe I didn't really need it.
80 square feet of heated space I want to stay VERY warm (50+) with little effort even when it's below zero....ya, I'm thinking I better spend the bucks
If you are putting this under concrete, use 250 density. Also don't forget 6mil poly.
The makers and sellers of the 25 psi density would like you to believe that so they can sell a product that costs more. However, some math reveals that for normal residential use the 25 psi foam is unnecessary. I too believed that until the day an experienced professional home craftsman pointed out the error. This had been pointed out to him by a licensed professional engineer.
see this post... (http://countryplans.com/smf/index.php?topic=7672.msg172558#msg172558)
In the end I went with the R10 'Styrofoam' (Blue) insulation as that's what the supply had (since HD sold all their pink).
Pricing was almost identical so it wasn't much difference.