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How do I prevent my kitchen sink PEX lines from freezing?

ps24eva | Posted in General Questions on

I cut the drywall from my finished basement ceiling above a basement window.

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  1. Expert Member
    Dana Dorsett | | #1

    Air seal & insulate the basement walls (preferably to IRC 2015 code min, but even less would do) and it'll be fine, unless you insist on keeping the basement window open.

  2. ps24eva | | #2

    Basement is finished already.

    I cut out drywall in the ceiling for the pic above.

  3. GBA Editor
    Martin Holladay | | #3

    It's hard to give good advice unless we know your geographical location or climate zone.

    If you live in Fairbanks, Alaska, you have to go to extraordinary lengths to keep basement pipes from freezing. If you live in Atlanta, Georgia, your basement shouldn't freeze, especially if even rudimentary attempts were made to air seal the basement.

    In almost all climate zones, frozen plumbing pipes indicate an air leakage problem, not an insulation problem.

  4. Expert Member
    Dana Dorsett | | #4

    If it's actually freezing in a finished (even uninsulated) basement it is almost certainly an air leakage problem. The drain in that picture would be susceptible to icing up too.

    The advice is still air-seal & insulate, where you can. If can't find the air leaks at the wall & window framing (the window framing being a prime suspect, but the band joist and foundation sill are also high on the list), you could caulk the joist bay where the plumbing runs and box it on the underside with an inch of rigid foam, which puts the plumbing in the same conditioning zone as the first floor.

    But an air leak big enough to freeze pipes in a joist bay is worth spending some time & energy chasing down.

  5. ps24eva | | #5

    There is definitely cold air coming from the window framing.

    How is my plan:

    1. Spray foam window framing with Great Stuff and put a section of rockwool batt on top
    2. Put poly iso foam blocker in joist bay
    3. Put polyethylene pipe sleeves on the PEX lines

  6. user-2310254 | | #6

    You can use the Great Stuff window and door sealant on the windows (and doors). As Dana said, you don't want air infiltrating into your house. You never indicated where you are located, but it must be a cold climate for a "finished" basement to drop below freezing.

    I am suspicious that your basement area was finished correctly. You might want to review this article ( and then undertake a little detective work to see how much remedial work is needed.

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