I have PEX pipe hung under the floor joists in my crawl space. I am inclined to cut fiberglass wall insulation R-14 into strips and run it under the pipe.That will encase it as the floors are well insulated. (R-19 above the PEX & R-14 below) Would that be as effective - less effective - more effective than putting foam insulation around the exposed sections of PEX ?( I really don't want to pull the hangers that attach the pipe to the joists) The cost of insulating this was would be negligible but I don't want to create any moisture problems? The crawl space has a good vapor barrier on the ground. the insulation in the joists has no paper backing.

  • where are you located?
    – DMoore
    Commented Apr 6, 2015 at 16:06
  • I am located in Twin Falls, Idaho... There is little likelihood of freezing in this crawlspace. There is good insulation in the floor, the PEX is hung on the bottom on the joists, so I would be adding insulation under it.It would be like having it in the center of the batts, I am just not sure if the cost savings would be enough to do it. I would like to save the water we run to get hot to the faucets.
    – Pat A.
    Commented Apr 7, 2015 at 22:47

1 Answer 1


Should work fine-ish. Use more UN-Faced insulation to avoid moisture problems.

It's only fine-ish (rather than fine) because the pipe is more than halfway through the total insulation, leaving it somewhat subject to freezing if it gets cold in the crawlspace.

  • I agree. Also rodents/critters hate fiberglass. Anything else actually might be a nest opportunity (other than spray foam).
    – DMoore
    Commented Apr 8, 2015 at 4:18

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