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Slab on grade insulation for infloor radiant?

pesumm Member Posts: 1
Is using Reflectix for the insulation beneath your slab acceptable? I used 4x8, 2" pink foam all along the perimeter (so there is 8 ft of pink from the wall to the center of the floor all along the perimeter), and then used 2 sided Reflectix for the "center" insulation. All gaps were sealed with reflective tape. I have 4" of pink foam going about 6" into the ground (vertically) all along the perimeter as well, with Reflectix overlapping the gap where the vertical and horizontal pieces of pink foam meet.


  • MikeG
    MikeG Member Posts: 162
    Personally I would have saved my money and put it all into 2" foam under the whole floor. Any reflective or bubble insulation under a slab is the same value as a bread wrapper. Perimeter insulation is critical to separate the floor slab from the outside. Just from my experience.
  • Jamie Hall
    Jamie Hall Member Posts: 16,599
    The reflectix type insulation works after a fashion for radiant heat. Unfortunately, that's not what you are dealing with underslab, and it won't do any more good than the same thickness of polyethylene sheet would have. Which is to say, nothing. If well sealed, it will be a decent vapour barrier, so it isn't a total loss. Sorry about that...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • kcopp
    kcopp Member Posts: 3,784
    If you want to reduce the budget a bit use 1" XPS in the center instead of the full 2"... Bubble foil is garbage.
    GordySWEIdelta T