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Radiant floor heating: Which way should my vapor barrier face?

NB2AqZqdjm | Posted in General Questions on

I have a question about which way my insulation should face in my particular application. I own a 2 story house sitting on top of a partially below grade basement. The house was built in 1946. I just installed radiant floor heating through the whole house by running 7/8″ PEX up and down every floor joist cavity. Heat deflection shields were stapled over the PEX all along its route to disburse the heat better to the floor.

My question concerns the basement. The basement is not a finished space but it will before too long. My plan is to have a home gym, a laundry room, and my giant wood shop. I’ll probably just use a space heater in those areas since their usage will be low and intermittent. In the basement, in the floor joists for my heated 1st floor, I put in a radiant barrier 2″ below the PEX, and R-30 insulation below which fills the 2×10 joists completely, leaving the small air space for the PEX to heat. The R-30 insulation is Kraft faced and I installed it with the Kraft side towards the basement (the cold/unconditioned side). I live in the Northeast, so it’s a cold climate, and common practice is to have the Kraft side always face the warm side. I wasn’t aware of that until now and I’m about 75% done installing the insulation.

I called the radiant company that I bought everything through and they said I installed it correctly. But this seems to go against common practice. Should I flip all the batts over or leave it alone?


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  1. GBA Editor
    Martin Holladay | | #1

    Ideally, you wouldn't have kraft facing on the cold side of your floor. But your basement is unlikely to get cold enough for problematic moisture to condense on the vapor retarder.

    If the fact that you made a minor mistake bothers you, you can remove the kraft facing without removing the fiberglass insulation. Or you could slash it with a knife repeatedly.

    As you probably know, kraft facing should never be left exposed because it is a fire hazard. If you decide to leave it, you'll need to install drywall on your ceiling.

  2. Riversong | | #2

    I agree with Martin that the kraft paper orientation is not going to make much difference, and if your basement is more humid than the upstairs it may be better to have the vapor retarder on the bottom.

    You cannot, however, simply remove the kraft facing since the batts are sized to fit easily into the joist bays and will fall out. Unfaced batts (which is what I always use on the rare occasions I use fiberglass) are overwidth to allow a friction fit.

    Ditto, also, on covering the faced fiberglass batts with an ignition barrier as well as something to contain the carcinogenic glass fibers and the fomaldehyde binders.

  3. NB2AqZqdjm | | #3

    Thanks so much for the info guys. And thank goodness I don't have to flip all the batts over, phew!!! I'll leave the batts installed as they and install drywall ceilings as an ignition barrier. Thanks!!!

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