(206) 949-5683, Top Rated Plumber, Seattle
Results 1 to 2 of 2

Thread: Insulating radiant floor installation with exposed beams

  1. #1
    DIY Junior Member pediwent's Avatar
    Join Date
    Dec 2009
    San Francisco, CA

    Default Insulating radiant floor installation with exposed beams

    I just had radiant floor heating installed in my second story with the PEX tubing clipped to the subfloor from underneath in the garage. Most of this I plan to insulate with R-19 fiberglass batts followed by drywall (I am finishing the garage as well), but in one section I would like to leave a couple inches of the floor joists showing (I have nice, thick, redwood joists and am looking for the exposed beam look). In this area, I was planning on nailing a 2x2 along the edge of the joist and placing 2" rigid foam insulation on top of the 2x2 and screwing 5/8" drywall to the bottom. Would this provide adequate insulation?
    Attached Images Attached Images  

  2. #2
    In the trades Dana's Avatar
    Join Date
    Jan 2009


    2" of XPS (blue/pink board) is good for R10, which would be fine if it's over conditioned space, but you say this is a garage. If the garage is normally heated to 60F+, it's enough, but if it normally drops below 50 on cold days, more insulation is usually cost-effective. If it ever freezes in the garage you need at least R20.

    If this is suspended tube ("clipped to the subfloor" sounds like it is) use foil-faced iso, which gives you a radiant-barrier effect. The emissivity of the wood subfloor is high, and it'll be re-radiating a significant amount of heat downward, as will the PEX, when running at the higher water temperatures required for un-plated staple ups.

    If it's plated tubing (heavy extrusions or sheet metal), don't leave any air gap- snug it right up there. In fact, if it's plated you might consider using OSB instead of gypsum, and dense-packing 5.5-6" of cellulose in there. With plates the heat transfer from the tubing to the floor is 95% conducted, 5% convected, sub-1% radiated. Aluminum has extremely low emissivity, and the radiated heat flux downward is quite small in plated systems (don't waste time/money on radiant barriers in plated radiant applications.)

    If you're leaving an air gap between the insulation & the tubing (or if you use batt fiber insulation), spray-foam seal the ends of the joist bays to prevent thermal bypass currents from flowing in the gap whenever there's a pressure differential between one side of the garage and the other. A slight breeze will find every infiltration point, and it's leaking air into the gap the insulation cant' do it's job. (A well insulated wind tunnel is impossible to heat, eh?)


Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts