renovating a home w/ unsulated concrete slabs. We will be installing radiant heating w/ hardwood flooring. I want to add some insulation on top of the slab & thought of 1″ Ridgid insulation w/ 3/4″ CDX ply on top power nailed or Tapcon screwed to slab. Dow make a board w/ a compression rating of 25 PSI.Has anyone tried this w/ any success?
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Don't quite understand. Do you want to do radiant heat ATOP your uninsulated slab? Or is the slab in the basement and you are doing radiant under your wood floor deck structure above?
How much total thickness build can you tolerate?
What is your climate zone?
Have you considered 2x sleepers on 16" centers, running your PEX tubing loops in between, and gypcreting?
How about QuikTrak atop rigid foam, screwed all the way through into the slab, and then the wood floor directly on top of that?
doing radiant on top of a slab on grade. From everything I've read about quicktrack you need 5/8" ply or better to screw the quicktrack to. If I go sleepers & ply I still need to insulate, thought I could save a headache & use 1" ridgid w/ 3/4 cdx. I have 9' ceilings & frame all doorways to 85" to allow for what ever the finished height becomes.
Don't worry about the heat breaking down the foam; water temps for radiant are around 95-105 deg F, not hot enough to cause problems.
If your in a cold climate and since you have the ceiling height, go with at least R10 insulation and may be R15. The temp difference between the heater (the piping at 100* F) and the soil (probably 50* F) is 50. This is similar to having the room temperature set at 70* and the outside temp being 20*- a 50* difference again. We'd want exterior walls of at least R12 and preferably R20; so the R15 is not bad for the floor, maybe a bit much...but no lower than R10 is recommended.
Thanks for the info.
You're on the right track- if there's no insulation under the slab, don't heat the slab itself or you'll be losing a great deal of heat to the earth. You'll need a good 2" of foam insulation between your tubing and the current slab surface.
Personally I wouldn't be comfortable with putting heating tubing right on top of either EPS or XPS foam, for fear that the foam breaks down over time from the heat.
Perhaps you could embed your tubing in a thin slab on top of 2" of foam, though. Depends on whether or not you can spare this much space. The slab would distribute the heat a bit, reducing the tendency for the foam to break down over time, but I'd get some advice from the foam mfg before proceeding.