How to Insulate a Soil Stack

LESLIE: Peter in Alaska, you’ve got The Money Pit. How can we help you?

PETER: Well, I’m having trouble with my soil stack up my house, the vent – the main vent – going out. In the wintertime, it freezes solid and I don’t know what to do about it.

TOM: Let’s see. Tell me about the structure of your house. So the soil vent goes from your bathroom, up through your attic into – though the roof and out?

PETER: Correct. And it’s a two-story house. It’s very well insulated. I have R-32 walls and R-83 ceiling and I have double walls in my house. And the attic is vented along the ridge and it also has gable vents.

TOM: And is it freezing over at the cross – the top of the vent?

PETER: No. It’s down a little bit and my vent is up high. I got it about 4 feet down from the peak of the roof and it stands about 4 foot up from the roof.

TOM: I wonder if you were to insulate that soil pipe, whether it would be warm enough to prevent the freezing from forming down deep in it, if you were to insulate it right up to the point where it exits the roof.

PETER: I thought about that. I did that for our vent that’s over the stove, because I thought of the heat going up through there might condensate with the cold metal. So I did insulate that. So I was thinking maybe that would work. I don’t know.

TOM: I would. That’s a really easy thing to do. I would definitely think about giving that a shot. Because the moisture that’s getting out there is obviously a lot of water vapor. And if we can keep that pipe from freezing, the less chance you’re going to have to get that ice buildup. And then probably what happens is you get gurgle-y pipes because you’re not getting any air out of it. Things don’t flush right and all that.

PETER: Exactly. Yeah, I am concerned about it. And everything is heated, you know? Our toilets are hot water.

TOM: I would try that. I would insulate it. It’s a very easy thing to do and you’ve already got a terrifically insulated house, so why not just extend it up the other side of the roof?

PETER: Yeah. Alright. Thank you very much. I’ll try that.

TOM: You’re welcome. Good luck with that project. Thanks so much for calling us at 888-MONEY-PIT.