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Insulation for radiant heating between subslab and cast surface

we are in the process of installing radiant floorheat in a remodel project. we have 1 3/4" buildup, in which we will be running 3/8" tubing. There is an existing slab on grade to which we will be clipping our tubing.most of the products i have found that would be appropriate for this application are over 1/2" thick...this thickness seems a bit much, as that brings our net thickness down to 1 1/4", and includes a vapor barrier and foil backing. I have found a cork underlayment in 1/8". does anyone have any ideas or input on this situation or suggestions of a radiant heat insulation that is less than 1/4"?

thanks in advance for any help with this issue



  • CMadatMe
    CMadatMe Member Posts: 3,086
    Don't mean to be rude

    You stated that 1/2" thinkness seems a bit much. Do you mean that you feel it's a bit much, meaning you don't think that is necessary or that you have an issue with meeting up with a doorway or another room? 

    You could use a bubble wrap for radiant that will cover as both your vapor and insulation. You can then shoot down a product such as Wirsbo Quik Trak or some similart type of panels. What is your finished floor surface?  I think no matter where you go you are going to be 1-1/2" or so to the top of the finished floor.
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • NRT_Rob
    NRT_Rob Member Posts: 1,013
    not really

    bubble wrap isn't really insulation. anything with foil will be a waste of time and money here. Never use Bubble anything, ever, for any reason... and under a slab, never use anything with foil or calling itself a "radiant barrier". they are ALL junk products.

    nothing under 1/2" is much for insulation.

    The minimum measure I would take here is 1/2" of rigid foam (or "The Barrier", which despite the name is actually a foam product) with wire mesh on it to tie the tubing to. and that would hope that your slab isn't a huge source of heat loss: depending on where you are I would use much thicker insulation.

    You can also use something like Roth Panel which is either 3/4" or 1" thick, has real foam insulation and an aluminum top layer for tubing attachment built in. then you float a finish floor over it. you can get total building under 1-3/4" pretty easy that way, and get something more like actual insulation under it.
    Rob Brown
    Designer for Rockport Mechanical
    in beautiful Rockport Maine.
  • Abrhm
    Abrhm Member Posts: 1

    Chris, no worries...I am glad to get any input on this issue! here is some clarification on our project.....we are pouring a finish slab, we have 1 3/4" to work with. this heigth is determined by thresholds and finish floors elsewhere in the house. we have a an existing sub slab we are pouring over. We are looking at using 3/8"pex tubing, fastened to subslab with clips. The concern about insulation between the finish slab and the subslab is to provide some sort barrier to act as a slip sheet between the 2....our biggest concern is possible cracking in our finish slab, as it is only 1 3/4" (this dimension needs to contain our "insulation" and 3/8 pex)....another concern that has been raised is possible issues with expansion in the pex tubing, does anyone have input on tubing options available that do not expand as drasticly as pex tubing?.....at this point due to thickness issues I am not comfortable giving up more than 1/8-1/4" for the barrier between pours (if I went with a 3/8 net insulation and pex tubing over that I will only have 1" of concrete over the top of the pex....this is too thin to trust not to crack)

     I appreciate the thoughtfull replies to my post, and feel lucky to have this resourse to gain information!

  • CMadatMe
    CMadatMe Member Posts: 3,086
    edited November 2009
    Concrete Underpad

    Take a look at this product. I attached a spect sheet. You can find more inforation at www.tvmi.com. I have used there Ultra Barrier Product in the past and have some good success with it. This pad is only 5/16 thick. Another product ultra board will give you at a min a R-5 and is 1/4" thick
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
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