Terminating my vent stack

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meyestone

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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
 

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this is what he was talking about. the wind currents will blow the stank away or catch it and pull it down the pipe needs to be at or above the elevation of the highest point on the roof
3d1.png
now, your roof vent. the pipe BY CODE should be 4'' THROUGH the roof
NOT 2''or 1.5''

1_8_bend.png
 
If you feel you have a blockage in your vent line call a drain cleaning company and have them run a snake
down through the vent. Let them know what you have as the machine will probably take two guys to get
it up on the roof.
 
The only thing you can do with the 1 1/2 vent is to cut it near the roof and use an 1 1/2×2 or 1 1/2×3 coupling and extend from there normally this is done before going thru the roof I have seen vents with a 90 and a st 90glued together
My code requires the vent to be 18-24 inches above the roof
 
Thanks to all.

frodo, thanks for that. Now I understand what he was saying! Note that it's a cathedral ceiling (no attic). (I had to put a flat roof membrane on it because of ice damming.)

TomFOhio, I will try it first without renting a snake - I'd rather not be up there at all, as the snow is already here! The mystery of the water will have to await spring.

Geofd, thanks, I will do that, so that the 3" will still be inside the 4", which will hopefully prevent frost closure. And yes, I'll need to go up at least 24" to address the depth of the snow!

I'll put it all up unglued, and see how it goes over the winter.

Thanks again to all.

Cheers,
Michael
 
frodo:

Indeed, opening it up from the inside to enlarge the pipe before it goes through the ceiling would require taking apart the inside wall of our bedroom. I could do it, but as a last resort!

I do fully appreciate the concern about frost closure. However, my theory (or hope) is that since it's a cathedral ceiling (no attic), the house "leaks" a lot of heat directly to the roof surface (it melts all the snow, for example). This heat may prevent the 1 1/2" pipe from closing. At least, that was my plumber's theory!

Thanks again for responding.

Cheers,
Michael
 
frodo:

Indeed, opening it up from the inside to enlarge the pipe before it goes through the ceiling would require taking apart the inside wall of our bedroom. I could do it, but as a last resort!

I do fully appreciate the concern about frost closure. However, my theory (or hope) is that since it's a cathedral ceiling (no attic), the house "leaks" a lot of heat directly to the roof surface (it melts all the snow, for example). This heat may prevent the 1 1/2" pipe from closing. At least, that was my plumber's theory!

Thanks again for responding.

Cheers,
Michael
Mike, I apologize, i failed to make myself clear.
What i m proposing is doing ALL the work while on the roof

Yo have a 1.5 pipe through the roof
you want to install a 4'' pipe
cut a 4.5'' hole in the roof with the 1.5'' pipe being the center of your hole.
reach down through the roof into the space and cut the 1.5'' pipe
add a reducer then insert a 4'' pipe.
install a 4'' flashing
 
re the frost issue. we have that problem here. I have an 1 1/2" pvc vent line and was going to increase it just like you are thinking about. The guy at home depot said try painting it black first. I gave it a try. at 35 below, we did not get that frost closure. I sure was surprised it worked. 5 minutes and a can of black spray paint sure was easier.
 

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