Venting under slab in basement, see my layout, where to add?

Posted by Joe Sloppy on August 15, 2005, 3:00 pm

I am adding a bathroom in my basement complete with toilet, tub,
shower, and sink. I believe I have the drainage system down but I
don't quite have the venting figured out. I bought a book with about
10 full color pages on how to vent plumbing properly but I still am
having trouble figuring out what I need to do exactly. If you open the
pdf or jpeg at http://www.kcengineer.com/piping.jpg or
http://www.kcengineer.com/piping.pdf you will see my current layout. I
have added letter to the pipes to aid in telling me where to come off
for vents. If I understand correctly, I would only need to add a vent
to the pipe labeled C which is between the shower trap and wye for the
tub. Doing that I assume would allow the shower, tub, and toilet to
pull air from that vent and not sucking water out of a trap. The sink
will have a mechanical vent you can buy for about $5. Then again, maybe
I don't need any vents as I did run 4 inch all the way to the toilet
and 2 inch all the way to each fixture so the pipe may just vent itself
because the top half would never be full. I am confused as what to do;
this is my only option for layout of piping because of space
restriction. By the way, the longest pipe is D, about 7' long. The
rest are all 3' or less sections. Thanks for any advice!

Posted by kevin on August 15, 2005, 7:09 pm

You might want to find a plumber who can answer your question. Or a
competent inspector, who will have to check your work anyway (right?).
Venting can be tricky, and if you are putting this in concrete, then
you want it done right.

As an aside, I think you certainly do need some venting. Imagine a rush
of water coming down the stack, past your whole layout here. It would
tend to pull air out of ALL of the traps, and the toilet. There are
rules about how close the vent needs to be to the ptrap -- having to do
with how much elevation is lost between the ptrap and the vent, and the
pipe diameter. I would guess that perhaps the 2" vent in C would
probably work, or at least, it seams at least plausible that it might
be at least part way to being what you need, most of the time.
Depending. And YMMV. To meet code, you would probably need at least two
vents, much closer to both the tub and shower.

Posted by CL (dnoyeB) Gilbert on August 15, 2005, 11:42 pm

Joe Sloppy wrote:

> I am adding a bathroom in my basement complete with toilet, tub,
> shower, and sink. I believe I have the drainage system down but I
> don't quite have the venting figured out. I bought a book with about
> 10 full color pages on how to vent plumbing properly but I still am
> having trouble figuring out what I need to do exactly. If you open the
> pdf or jpeg at http://www.kcengineer.com/piping.jpg or
> http://www.kcengineer.com/piping.pdf you will see my current layout. I
> have added letter to the pipes to aid in telling me where to come off
> for vents. If I understand correctly, I would only need to add a vent
> to the pipe labeled C which is between the shower trap and wye for the
> tub. Doing that I assume would allow the shower, tub, and toilet to
> pull air from that vent and not sucking water out of a trap. The sink
> will have a mechanical vent you can buy for about $5. Then again, maybe
> I don't need any vents as I did run 4 inch all the way to the toilet
> and 2 inch all the way to each fixture so the pipe may just vent itself
> because the top half would never be full. I am confused as what to do;
> this is my only option for layout of piping because of space
> restriction. By the way, the longest pipe is D, about 7' long. The
> rest are all 3' or less sections. Thanks for any advice!
>

I was looking into the same thing and did a lot of internet searching.
Its tough to find good info but i managed to find one place where they
really discussed a lot. Cant remember where. I was hopin you got more
responses so I could see what people said.

From what I read the vent would have to be directly in the pipe B
downstream from the toilet. The way it was recommended is that there
would be a vertical pipe on B that the sink would connect to. and a
mechanical vent on top of that pipe large enough to vent for both I
guess. And the shower was allowed to run into the vertical pipe but not
the flat pipe. I am NOT a plumber, and only read this stuff on the
internet so I really dont know. but its what i read.

--
Respectfully,

CL Gilbert

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