Polyiso insulation under radiant floor heating slab?
I’m looking to install a radiant foor heating system in my house. I recently purchased a large amount of used (good condition) Polyiso Insulation namely RMAX Thermasheet Type 3 and some of Firestone’s equivalent.
Looking into it further I’m now wondering whether I shouldn’t have gone with EPS instead of Polyiso. (Sounds like Polyiso has issues with moisture wicking and decreasing R values in cold temperatures).
Seeing that I’ve already bought it, I’m wondering if in my particular situation Polyiso will work – The 4″ of Polyiso will be installed onto an existing slab and sandwiched top and bottom with 6mil poly vapour barrier. I will not be putting any holes through the top layer as the pex tubing will be fastened to rebar mesh with zip ties. The rebar mesh will be raised up with 1/2″ wide foot plastic spacers to avoid putting holes in the vapour barrier.
The house is located in Interior British Columbia. I have attached a cross-section diagram of my plan. Any advice, experience or opinions are much appreciated!
Thanks for your time!
GBA Detail Library
A collection of one thousand construction details organized by climate and house part