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  1. #1
    Join Date
    Jan 2013
    Posts
    1

    Default insulating joists under infloor heating pex pipes

    What is the best method for insulating under the floor heating pipes that have been attached below the floor between the joists?

  2. #2
    Join Date
    Mar 2008
    Location
    nova scotia, canada
    Posts
    1,522

    Default Re: insulating joists under infloor heating pex pipes

    insulate the pipes first, then use fibreglass batts
    fire up the saw and make some dust

  3. #3
    Join Date
    Dec 2007
    Location
    Tennessee
    Posts
    1,381

    Default Re: insulating joists under infloor heating pex pipes

    Is the floor above a basement, a crawl space or first floor.

    If this is over a crawl space, first insulate the rim joist. Then you have a number of choices. One that would work is 4x8 sheets of foil backed foam. 1/2" or 3/4" thick will be enough, just nail it to the bottom of the joists and seal the joints with a foil tape.

    You can stuff 3.5" unfaced batts between the joists at the bottom so there is an air gap above the batts. Hold it in place with strapping, string or what ever. If you use strapping, space it about 6" apart, no further or the batts will sag.

    You can use faced batts too if you want, just fold the paper wings down the sides of the batts and insert the batts paper side up. The batts should apply pressure to the wings to hold them against the joists. again, leave a large gap above the batts and secure with strapping or string or wire.

    You can even just use a heavy weight vinyl sheeting stapled to the bottoms of the joist as long as the rim joist is well insulated. As long as you trap the air, the warmest air will stay against the floor. In a floor, still air is worth about an R-3 per inch. This does not apply to walls or attics because the air will not stratify in those places like it does in a floor.

    If you use string or wire, the quickest way to install it would probably be to use crown staples.

    You can do basically the same thing if you have a basement except the rigid foam board option.

    If its between floors, insulate the beltline (rim joists) if you have ready access, then unfaced batts at the bottom of the joists and install the ceiling material.
    Last edited by keith3267; 01-06-2013 at 05:21 PM.

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