I need advice on a plumbing code question. My existing 1st floor
bathroom vanity appears to use the drain from the 2nd floor toilet as
a vent stack. Appears that both 1st and 2nd floor toilets have no
other fixtures draining into their respective drains.
Question: does the plumbing code allow me to route the 1st floor
vanity drain into the same drain from the 2nd floor toilet (which is
being used as a vent for the same vanity)? Or must I continue to have
a dedicated drain for toilet?
See sketch at:
(If this is not the appropriate way to reference an image on this
newsgroup, please advise and I'll change).
Your comments are appreciated.
re: Aren't wet stacks only allowed on the same floor?
I hope not! My 2nd floor bathroom, 1st floor sink and 4 basement
fixtures (full bath and utility sink) all use the same wet stack.
There are no dedicated vents for any fixtures in my house.
The 1st and 2nd floor fixtures drain into the cast iron vertical stack
and the basement fixtures all connect to the cast iron drain pipe
under the slab. Everything works fine as far as I can tell. The only
drainage problems I've ever had in 24 years were caused by roots in
the town owned section of the drain out by the street.
There is/was an exception in the case where the soil stack
is 4" size. In this case, the 1st floor and 2nd floor
toilets may join the stack without additional venting.
Lav trap could empty above the uppermost toilet.
Today, you probably couldn't do things like this,
but it was accepted practice and did work.
I believe the cast soil stack is 4" so I guess my house is
However, this statement confuses me: "Lav trap could empty above the
The uppermost toilet is on the second floor, and obviously the toilet
drain is on the floor. How could anything empty *above* this?
Both the sink and tub empty into the pipe that the toilet sits on,
just a few inches below the shoe.
Ah. That's a side-inlet to the "closet bend".
It wouldn't normally be done without some vent
provision, but could have been allowed by local
exception. It worked and that was the ultimate test.
Over the years, every state/county had their own
interpretation of what constituted good practice.
Unlike the Electrical Code, we never had just one
I have a little trouble following your sketch.
Where is the roof vent terminal?
In any case, NO the Lav vent can not be tied into
the stack *below* any toilet. This is not what
is meant by a "wet vent".
The Lav vent must be extended up thru the 2nd floor
to a point above the toilet connection or else
have its own vent thru the roof.
Your question of "where is the roof vent terminal" for the lav is
exactly why I find the existing condition peculiar: the 1st floor lav
vent ties directly into the stack *below* the 2nd floor toilet. If
this layout is not the definition of a "wet vent", I think I'll have
to extend the vent up as you suggest (please confirm).
Then, assuming the vent is rerouted and the issue resolved, is there
any restriction you can think of against tying the lav drain directly
into the stack below the 2nd floor toilet per the proposed sketch?
I had the same setup and was required to update it to current code when I did
some renovation last year. I had to move the downstairs vent so they connected
into the stack above the point where the upstairs waste tied into the stack, so
that water from above could not flow past the vents. It can be a small vent, I
ran 1 1/2" PVC alongside the stack and reconnected in the attic.
On Thu, 01 Nov 2007 06:11:00 -0700, anthonymmfalcone wrote:
If you are unable to extend vent to roof or above 2nd floor toilet,
consider using a mechanical vent installed at the sink. Just remember to
keep it accessible for inspection and maintenance.
Although not the best solution, it will work and may be permissible.
Good question to ask your local plumbing inspector. Sometimes codes vary
from locale to locale.
HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.