Radiant floor heating logistics and insulation materials
Objective: install ceramic tile above hydronic radiant floor heating on existing basement slab.
Zone: 4 (Marine)
Existing conditions: 4 inch uninsulated slab over polyethelene barrier installed in 1974, over crushed stone. Floor to bottom of joists is about 7.5 feet.
6 mm polythelene sheeting or Delta-FL (8 mm) on slab
1/2 inch rigid foam over moisture barrier
3/4 non-PT plywood ripped into 12 inch segments with 3/4 inch space between pieces to hold the 1/2 inch PEX tubing over rigid foam
1/4 inch substrate over plywood and PEX
Ceramic tile over substrate
1) I am assuming the 1974 poly sheet beneath the slab is either not present or not working out of an abundance of caution. (It is depicted on blueprints.) That motivates me to put down a moisture barrier on top of the slab. Do you see any problems with doing so?
1a) Any advantage of Delta-FL over (much cheaper) 6mm poly sheeting?
2) For the 1/2 inch rigid foam, EPS, XPS or Poliso? I’m a DIYer and keep reading different answers.
3) For the substrate, thoughts on 1/8 inch Ditra mat versus 1/4 inch Hardibacker? (Cost difference is about 50 cents psf, on a 600-800 foot job.)
4) Finally, part of the basement is a utility area. I had planned to leave that area entirely unfinished (walls, floors, ceiling). If I leave the floor uninsulated, is there concern that all moisture in the slab will just move to the uninsulated area and enter the basement there? My question is, should I just finish this part of the basement floor, too, but skip the hydronic heating in the floor area?
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