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Radiant above uninsulated slab

baltik
baltik Member Posts: 21
edited September 14 in THE MAIN WALL
What's the best way to add radiant over uninsulated slab, I am in a moderate climate but am sensitive to build up height (the area has low ceilings already).

My current thinking is:
1" of foam panel above the slab, using an adhesive
attach pex to the foam panel
pour 1.5" gypcrete
floating engineered wood floor above


alternatively:
1" of foam panel above the slab, using an adhesive
plywood glued on top with routed grooves for pex
optional: aluminum transfer panels
nailed engineered wood floor on top


would love to hear some feedback or alternatives

some approximate examples of these setups I've found:


Comments

  • hot_rod
    hot_rod Member Posts: 16,878
    It comes down to how much insulation value you want for the system. 2” would be nice, 1/2” bare minimum. 
    Radiant ceilings typically only add 1/2” for another option, same radiant feel, much less install hassle. Then engineered floor over 1/4” foam for some thermal break.

    Is it slab on grade, or a basement? Adding more than 1/2” on a basement floor should involve a stair case rebuild, as the lower step will be a trip and fall hazard. I think code allows 3/8” difference maximum 
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • baltik
    baltik Member Posts: 21
    Appreciate that - always a wealth of knowledge!

    it is slab on grade and stairs haven’t been constructed, so not concerned about that. My preference is to do floor radiant vs ceiling as the ceiling has many structural beams to work around.

    in the above scenarios is there any concern with using adhesive to attach insulation? I presume I should incorporate some sort of moisture barrier as well? What would be the best way to go about that?
  • hot_rod
    hot_rod Member Posts: 16,878
    While not a very thick insulation, I like the Roth Radiant panels. They only add 1/2- 5/8 and have a nice aluminum top layer. 6 or 12” spacing. Walk the tube in and float the wood right over it. Gets you a nice, quick responding system.  
    Tube it at 6” spacing for great surface temperature consistency.

    I use foam adhesive with a notched trowel to glue it down. If the floor is wavy put some weight on the panels 

    You could seal the floor first if radon gas is a concern. The glue with a notched trowel does not seal the entire floor. Any of the poly floor sealers with a roller should work. 

    It MUST be foam adhesive, regular construction adhesive will dissolve the foams. Find it in one or five gallon buckets
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • psb75
    psb75 Member Posts: 584
    If there is RADON...you'd better be doing more than just sealing the floor. Better plan for radon remediation. That includes venting air pressure underneath the slab. Usually involves concrete "coring"-drilling in the slab and either a passive or mechanical venting up and out-- above the roof.
    hot_rod
  • hot_rod
    hot_rod Member Posts: 16,878
    @psb75 good idea, Radon testing is included in most real estate contracts now. A good idea to test before you start covering the slab. It usually an easy fix, looks like a 4" dryer vent and blower piped to the outdoors. There are companies that specialize in that work, often a 1 day job.

    Realtors have these companies on speed dial, as it makes or breaks a sale!
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • psb75
    psb75 Member Posts: 584
    You got that right Bob!
    Radon re-mediators leave a visible water-column gauge inside the house, on the vent pipe to show vacuum.
  • baltik
    baltik Member Posts: 21
    edited September 15
    I've never heard of Radon in our area, so thankfully not a factor. I'm still a but fuzzy on where to integrate the moisture barrier, the concern is that the adhesive wouldn't have much hold then...

    https://county-radon.info/CA/Marin.html
  • hot_rod
    hot_rod Member Posts: 16,878
    A sealer like this, penetrates and should still allow you to mastic or adhesive over it? Check with the manufacturer
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
    baltik