I am adding a first-floor bathroom to my 2-story + unfinished basement 1920s era home. In the basement, there is a 4" horizontal drain that runs from a chase in the middle of the house that extends to the attic, around the perimeter of the basement, to the main sewer line exiting the house. The new bathroom will have (in order from nearest the main 4" drain in the basement to furthest from the main drain line) a water closet, a shower, and a lavatory. The water closet will have its own vent extending up through an interior wall about 24" from the flange. The sink drain line will travel about 5 feet horizontally through the basement , then be joined by the shower drain line, and then will extend to the main 4 inch drain (the water closet enters the main 4" drain separately). The wall nearest the shower sits directly over a joist, so the vent cannot enter this wall from below. The next nearest wall is >5 feet from the shower trap. The lavatory sits against an exterior wall, but without tearing out the wall above on the 2nd floor, I can't run a vent through the exterior wall.

So here is the question:
Can I drop the lavatory drain down into the basement about 12" below the bottom of the joists, turn horizontal with a wye (with cleanout) and a 1/8 turn, then have a sanitary tee branching a vent vertically for 8", then 1/4 turn to horizontal extending to directly under the interior wall where the WC vent runs, turn up into the wall, then join the WC vent? Can I do the same with the shower vent?

In other words, can the vent for a lavatory and a shower run 8" above and parallel to the drain lines for the same fixtures, before turning vertical (then joining the WC vent, which then re-vents to the main stack in the chase to the attic)?

Hope this makes sense - if not, I can try to put together a diagram and post it...

A drawing would be helpful. What area do you live in and under what plumbing code do you fall under? Will a permit be pulled and this job inspected? Let me know, Tom

A drawing would be helpful. What area do you live in and under what plumbing code do you fall under? Will a permit be pulled and this job inspected? Let me know, Tom

Hi Tom - I live in Lebanon, NH - My plumbing code is the International Plumbing Code 2006 with a few amendments that don't pertain to this. A permit will be pulled, and the job will be inspected.

I'm trying to attach a drawing to this - I made the drains arbitrarily green and the vents arbitrarily blue just to make it easier to tell what is what. I have left the WC off, since it has its own vent and enters the main drain separately, so I just left it off for simplicity. The horizontal drains and vents that are 8" apart on the drawing (one above the other) are all in the basement, below the floor joists for the first floor.

Hope this clarifies things... thanks!
-Paul

Hi NH:

Here is a breakdown of the venting...

First pic. Is for individually venting the fixtures. The second picture is for wet venting the shower using the lavatory vent, but the drain and vent need to be increased to 2"...;)

Either way, you must run the vent for the lavatory above the floor at 42-48" above the finish floor. Run the vent back to the vent stack (or run parallel to waste stack until it becomes a vent stack) pitched at 1/4" pitch per foot so rain water can enter the vent at the roof and drain back down the drain line by gravity.

If you wet vent the shower be sure to roll the 2" WYE or SANITARY TEE fitting above the centerline of the waste pipe... what makes it a VENT! See image.

Let us know if you have more questions here...

MARK

Great - thank you for your prompt and thoughtful answer. Two more questions:

1. If I wet-vent the shower, is there a maximum distance allowed between the shower trap and the lavatory trap? As it is planned at this point, the distance between the two is roughly 54 inches...

2. Regarding slope of vents: do they always need to slope down going away from the main vent stack? Or is the key point just that they cannot have a "trap" in them - (i.e. they must slope so that they always drain somewhere if they should get some water in them). In other words, could one theoretically have a vent that slopes toward the main vent stack at the vent stack end, and slopes toward the drain at the other end, so that all points in between will drain somewhere, either to the main vent stack or to the branch drain?

Thanks!

Paul

Hi Paul...

1) The only distance requirement here is that the 2" lavatory drain needs to connect within 5 feet of the shower pTRAP.

2) You could do what you propose, but it is not how plumbing is done. All vents pitch away from the main stack toward the drain... PERIOD! Anything else is against plumbing code... ;)

If you look at the fittings you will be using to connect the vent to the stack you will see that the fittings are directional and will trap some water if you pitch in the wrong direction. Just FYI...

MARK