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Freezing Bathtub Drain -- how to improve exterior insulation

Posted: Tue Sep 10, 2019 11:15 am
by Robbo
I have a bath tub drain that froze solid twice last winter, and want to improve the insulation (we live in Minnesota). The tub drain pipe freezes but not the water inflow. Tub/shower is located at an exterior corner, so two of the shower walls are on exterior walls, and the plumbing is clearly on an outside wall with no interior access panel. I assume the tub drain connects to sink drain, and the sink works fine all winter.

I am looking for ideas/best approach, potential trouble spots and advice. I am certainly not an expert with this type of repair.
a) should i create an interior access panel and work from there? (this is difficult because toilet is
immediately outside the shower)
b) is it better to work from the outside?

I am able to access the area of the house that is directly outside where the tub drain freezes. Behind the j channel vinyl exterior siding i see what appears to be house wrap over rigid foam panel insulation. Not sure what is behind this. House was built in 1982, and we just purchased last year.

Ideas or Comments welcome

Re: Freezing Bathtub Drain -- how to improve exterior insulation

Posted: Tue Sep 10, 2019 11:37 am
by A. Spruce
Not surprising that you'd only have trouble with the tub drain, and this is due to design. A sink drain has the trap, the curvy part of the pipe that holds water to seal the pipe against backflow of sewer gas. A tub has this same trap, only it's under the tub and exposed to exterior ambient temps, so when the crawlspace gets below freezing, you're going to have issues with the drain. Odds are you don't have problems with your supply lines because they're insulated and/or protected more from freezing temps.

Not sure what kind of "cold weather" things are available, I would think that at least wrapping the pipe with a good amount of insulation would help, as would adding a heat tape around the trap area. This is the benefit of living in a warm climate like I do, I don't have to worry about such things. :P :mrgreen:

Re: Freezing Bathtub Drain -- how to improve exterior insulation

Posted: Tue Sep 10, 2019 6:00 pm
by Shannon
So do you have access from below the tub?

Re: Freezing Bathtub Drain -- how to improve exterior insulation

Posted: Tue Sep 10, 2019 6:19 pm
by Robbo
Shannon i don't have easy access from below tub, perhaps other than from the ceiling below. The tub is on second floor above family room.

Re: Freezing Bathtub Drain -- how to improve exterior insulation

Posted: Tue Sep 10, 2019 7:44 pm
by Shannon
Chances are you will have better luck working from the inside (under the tub) but you could try from outside first to avoid maybe having to cut the drywall down stairs. There must be a real problem with the insulation and our air/vapour barrier in that corner. Drafty areas can cause freezing problems if pipes are too close.