Insulation for slab on grade applications ie. snow melt or RFH.

MARS

I hope to get input on the debate about using a ridged polystyrene 1" insulation under a slab be it snow melt or slab on grade RF as opposed to using Insultarp under the the same. it is my understanding that the insultarp has a r value of 10 and that the 1" ridged has a r value of 5. I would like to hear about your instalations and the affects that these diffrent products have given you. Thanks Mars.

We know

Insultarp

Insultarp has an R-Value rating of R-10, but when you read the fine print, they tested that product with a 3" airspace in a wall. If you can use insultarp under any kind of slab and have a 3" airspace, please let me know how you did this??? Try using TVM R-foil Ultra Concrete barrier foil/BUBBLE-FOIL-BUBBLE. It has an R-value equivelency to 2" of blue board and have the testing to back it up

Unknown

The R10 is not true in a direct contact situation.

For me, it's pretty simple. Rigid polystyrene is all R value. You know it slows down heat transfer as insulation is supposed to do.

Products that attempt to "reflect" radiant energy in areas like slabs are much more questionable, as most of the heat transfer in those situations is NOT radiant in nature, it's conductive, and reflective insulation is nearly completely ineffective at reducing conductive losses. Keep the reflective insulation to wall and ceilings IMHO.

A bubble-foil-bubble product MIGHT be more effective that way, by creating a small airspace, but personally I would stick with what everyone knows works and knows how well it works. Unless that testing is really good; any links?

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Chris_32

Bang on

IMHO, I can not understand how there is any downward radiant transfer from something sitting on the ground. What I do seem to think is that those little bubbles allow the radiant transfer to start and that the value of the thermal conductivity break vs the allownace of radiant activity is potentially a major loss. I agree with rob that extruded board is all r-value and I feel that it is a major conductivity stopper which is what downward loss is all about.