Toilet upstream of lav - how to vent?

[mherman]

lavatory shares toilet vent?

thanks in advance for whatever anyone here can suggest. i've scanned this site and many others trying to find a similar situation, but can't find a clear answer.

we have an old pantry that's becoming a powder room. this is what i want to do. tell me where it's no good?

 

[Jimbo]

You can't use that san tee on its back....see lengthy thread above about that. Also, that vent line cannot be horizontal

 

[Sponsor]

 

[mherman]

oh, right... that whole thread. of course. okay, then... is there such a thing as 4x4x2 wye for vent? would that solve anything? run the drain all the way to the vent? like this... (or is that just a bigger horizontal vent?)

 

[Redwood]

How about wet venting the toilet using a properly vented lav sink.

 

[mherman]

How about wet venting the toilet using a properly vented lav sink.

not possible to go up from lav. the wall is shallow (2x2) furring on brick, has a finished floor right above it, and it's such a small room we've need a small pedestal sink, so even room to run it outside the wall.

if there was no sink, what's the proper way to vent the toilet by itself?

 

[Terry]

If the lav can't be vented through the roof, it will need a Studor vent.

 

[mherman]

mmm... if i understand your drawing, terry... you're adding the studor to my original plan, and changing my santee mistake to a wye? a few inches of horizontal vent are okay then?

 

[Terry]

The wye near the toilet is rolled upwards a bit.

The Studor go in by the lav.

 

[mherman]

thanks, terry, and the others who've chimed in. i've been checking out the studor and measuring how it can fit. the sink is a very small pedestal. drain to wall is only 6 7/8. so no room for the studor anywhere except inside the wall, atop the drain pipe. the wall is not deep enough for studor's recessed box. can i just make space in the wall and cover it with a small grill cover? would be accessible, but just barely... how long until it might fail?

alternatively, i have a 1 1/4" trap whose outlet end will be as tight to the wall as possible. outlet of trap is only 3" long, more water in the trap than the outlet from the trap. if i increase the drain inside the wall to 2", run the trap into a tee so i could put some air above the trap pipe, wouldn't these adjustments prevent a siphoning of the trap?

 

[hj]

drain

You are trying to rationalize doing a bad job. The lavatory MUST HAVE a vent, and a Studor vent is only a last resort to not doing it correctly. If you have enough room in the wall for the sink drain, and I personally would NEVER use 1 1/2" all the way to the 3 main line, you have room to run a proper vent. There might be more than one way to vent the toilet and lavatory properly, but we would have to be there to make the determination. YOU are only considering the one way and are trying to think of ways to make it work.

 

[Kingsotall]

YOU are only considering the one way and are trying to think of ways to make it work.

I hate that.

 

[mherman]

not rationalizing a bad job at all. AM actively looking for a solution that will work AND that is workable in the current construction of the room, i.e. not weaken existing structures AND that will not just look crummy. i know what looks good and not, i know what is inside and around these walls. i know how it looks in the book. what i don't know is some of the things that might actually work.

the best job, to me, is the one that works on all levels. so i'm just fishing around the edges of what i don't know, trying to understand better what the issues and possibilities might be.

can i run the vent pipe outside the wall and just paint it? if so, that might be aesthetically better than building a box around it.

would 3-4" of 1 1/4 trap tail direclty into 3" vertical drain pipe be self-venting, non-siphoning?

can i lengthen the pipe beneath sink to lower the trap? if so, how low dare i go with that? i think i need to drop it a least a little bit, so there's room for the studor, if i went that route, but don't want to drop it too far and make a too long, smelly drain pipe.

there is not really room for the pipe in the wall. the wall is 2x2 furring plus a little bit on the back of that, in some spots, but not dependably. one section of that wall was filled in years ago with concrete, sticking out an inch or more beyond the masonry surface. so furring was a bit difficult and there's no easy route inside that wall to the roof. so even if i tore a path floor to ceiling, close to the sink, it would still need to bump out of the wall significantly, which would be okay aesthetically, but might weaken the overall structure of the wall in ways that would be hard to put right.

looking again at running the pipe outside of the wall, but probably the studor is the way to go. so how/much to drop the trap can i drop the trap to make room for it?

 

[Terry]

Running the vent outside the wall would work.

 

[mherman]

do i need to be concerned about that pipe being very cold in the middle of winter? does warmer air rise out of the drain or cold air drop from the vent in the unheated attic?

 

[Gardner]

non-professional opinion and conjecture

The vent is open to the air at the top in any case, so having the length of the pipe exposed does not change things much. Other than condensation and precipitation there is no water in there to freeze. That said, in the town I live in vents can and do freeze up when there's a lot of snow.

 

[mherman]

i know it won't freeze, but wondering if such a pipe would be just darned cold to have exposed in the house when it was sub-zero outside. wondered if the air inside would be 50˚ rising out of the drain or very freezing, dropping in from the roof.

is there a simple extension pipe, or an extra-long sink drain pipe that would allow me to lower the trap under the sink, making enough room for a redi-vent to fit under the sink?

 

[Jastori]

If you can't go up from the lav with the vent, you could try treating it as an island sink - I believe that there are approved ways to vent those with a separate vent line that loops back under the floor, but you need to make sure it is done correctly (I am not a pro - and don't know the details).

 

[mherman]

yes, thanks. i was looking at that option last night, as well. it could work, but it could also end up being a really sloppy-looking solution. so i'm still puzzling on something that will be a bit more tidy. the drain line in teh wall has to jog out and run through the floor, so it doesn't hit brick immediately below the floor, under the wall. the loop vent would mean two pipes poking out of the bottom of the wall. might be cleanout issues as well.

the more i look at running a normal lav vent through the room, and figure all the crummy-looking things i might do to hide it, i think it's gonna have to be the redi-vent, extend the drain, lower the trap, and hide the redi in the wall behind a grill.

many thanks.

 

[mherman]

okay, so after a lot of puzzling and measuring and puzzling some more, i figured out how to run proper (i think) vent and hide the thing in a way that i think is solid and my in-house inspector (and her stricter code!) will approve. now... does this work for you guys?

 

[hj]

drains

Now you have gone overboard the other way. The line to the lavatory only has to be 2", and once you make the lavatory connection, your code MAY allow a 1 1/2" vent up the wall to the ceiling. If not, then just continue the 2" the rest of the way.