Hi all. I'm wondering why I don't want to have a 90 degree termination at the top of my vent stack.
Here's the story (thanks in advance for anyone who reads it and has any suggestions!)
We were getting sewer smells in our home. I called the plumber, who identified the problem as being that the vent pipe was blocked.
Up on the roof of our one-storey hone, there as a complicated end piece on the top of the stack, which my plumber had me simply cut off with a hacksaw.
What we found was that the vent pipe was a 1 1/2" ABS pipe. Where it exits the roof, there is a 4" abs pipe around it (the gap is stuffed with insulation, presumably to avoid frost closure.) There is a roofing sealant between the two pipes at the height of the top of the roof (thus, the exit from the roof is only 1 1/2", not the minimum recommended 3").
Sure enough, there was water visibly sitting in the bottom of the 1 1/2" pipe. We removed it with my shop vac, and sure enough, it started to smell at the top of the stack pipe, the drains started working better, and the smell in the basement was gone. I presume there must be a "low spot" in the stack pipe inside the walls, or some other kind of blockage in the vent pipe, which seems to have cleared.
My question is what to do now. I've got a 1 1/2" pipe and a 4" pipe sticking up about 18" from my roof (not enough given our snow loads here in Quebec.)
I understand from my plumber that the main idea with vent stacks is "draw", that is, like my chimney, if it's too short, it won't draw sufficiently and will "blow back", drawing sewer gases into the house.
I have two problems.
- First, how to I prevent frost closure? I know that my pipe should have transitioned to 4" before it went through the ceiling, but I can't change that now. If I extend both the pipes, should I put insulation between them?
- Second, how to extend and terminate the stack pipes.
My plumber told me to extend both the 1 1/2" and the 4", and to put a 22.5 degree angle on the 4" pipe. He said that heat escaping from the roof (it's a cathedral ceiling, so no attic) will prevent frost closure.
I don't understand why I would not put a 90 degree termination on the 4" pipe, so that the end would be pointing down, and thus no water could be able to get in. He seemed to think it was about catching the wind in some way I didn't quite follow. I get the you want to minimize the number of bends in the stack pipe, but I'd be putting the bend in the 4" pipe surrounding it.
Appreciate any advice and guidance that forum members may be able to offer.
Cheers,
Michael E.
LA Peche, Quebec
Here's the story (thanks in advance for anyone who reads it and has any suggestions!)
We were getting sewer smells in our home. I called the plumber, who identified the problem as being that the vent pipe was blocked.
Up on the roof of our one-storey hone, there as a complicated end piece on the top of the stack, which my plumber had me simply cut off with a hacksaw.
What we found was that the vent pipe was a 1 1/2" ABS pipe. Where it exits the roof, there is a 4" abs pipe around it (the gap is stuffed with insulation, presumably to avoid frost closure.) There is a roofing sealant between the two pipes at the height of the top of the roof (thus, the exit from the roof is only 1 1/2", not the minimum recommended 3").
Sure enough, there was water visibly sitting in the bottom of the 1 1/2" pipe. We removed it with my shop vac, and sure enough, it started to smell at the top of the stack pipe, the drains started working better, and the smell in the basement was gone. I presume there must be a "low spot" in the stack pipe inside the walls, or some other kind of blockage in the vent pipe, which seems to have cleared.
My question is what to do now. I've got a 1 1/2" pipe and a 4" pipe sticking up about 18" from my roof (not enough given our snow loads here in Quebec.)
I understand from my plumber that the main idea with vent stacks is "draw", that is, like my chimney, if it's too short, it won't draw sufficiently and will "blow back", drawing sewer gases into the house.
I have two problems.
- First, how to I prevent frost closure? I know that my pipe should have transitioned to 4" before it went through the ceiling, but I can't change that now. If I extend both the pipes, should I put insulation between them?
- Second, how to extend and terminate the stack pipes.
My plumber told me to extend both the 1 1/2" and the 4", and to put a 22.5 degree angle on the 4" pipe. He said that heat escaping from the roof (it's a cathedral ceiling, so no attic) will prevent frost closure.
I don't understand why I would not put a 90 degree termination on the 4" pipe, so that the end would be pointing down, and thus no water could be able to get in. He seemed to think it was about catching the wind in some way I didn't quite follow. I get the you want to minimize the number of bends in the stack pipe, but I'd be putting the bend in the 4" pipe surrounding it.
Appreciate any advice and guidance that forum members may be able to offer.
Cheers,
Michael E.
LA Peche, Quebec