Last week, we had a night that got down to -18F. In the middle of the night, the cold-water pipe going to the kitchen sink froze (but luckily did not burst). After some investigation, it turns out it froze where we had a dryer vent installed. The vent comes in between two floor joists, right where the sink's cold water pipe turns up and goes to the sink (see attached cross section image). The installer had removed a bunch of insulation from the bay between the joists, and not replaced it. The pipe is about 5" inside of the rim joist on the outside of the house.

To remedy the problem, I insulated around the dryer vent pipe, and put about 4" of fiberglass batting insulation on the inside of the rim joist (the thickest insulation that would fit between the cold water pipe and rim joist). I also wrapped the copper water pipe in foam pipe insulation.

Tomorrow night, it is supposed to get down to -30F. Does it sound like I've insulated things enough to prevent freezing? Would it be smart to shut off the main water supply, and drain the pipes for the over night, or can that cause other issues? Any feedback would be appreciated.

Cross Section

  • We had a similar scenario, except the vent pipe was touching a stubbed-off water pipe inside a finished ceiling. The dryer vent conducted the cold to the water pipe, and it froze during a cold snap; the next load in the dryer thawed it and gush! Luckily I was standing right under it and the main shutoff was nearby.
    – TomG
    Jan 6, 2014 at 3:54

2 Answers 2


What you have done sounds like a good start. Some additional steps I would take on the coldest nights is to allow the faucet to drip. You want it to drip as slowly as you can. Moving water takes longer to freeze than still water. In addition leave the cabinet doors open so that some of the kitchen heat will warm the pipes in the cabinet. Again these are steps for the coldest nights. On really cold stormy nights I put the heat on hold @68 degrees rather than setting it lower. This gives me a cushion in the event of a power failure.


No way to know if your fix is good enough. I use thermostatically controlled heat tape on my pipes in insulated crawlspace. Before I did that I used to let the faucet drip over night.

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