View Full Version : new tub p-trap, drain, vent size

01-28-2005, 11:52 PM
Hi - this is my first posting. We are installing a bathtub in our remodeled bathroom that previously had no tub, just a shower stall. We are keeping a separate walk-in shower and adding the bathtub adjacent to it. There is no room to connect the new tub drain line to the the main drain line because the shower drain and the bathtub drain in the bathroom next door leaves no space for an attachment. Could we run the new tub drain across the floor to the sink drain and vent? The sink drain and vent are 2'' - could we have a 4" tub p-trap and drain line and attach it via a sanitary tee to a 2'' drain line below or above the sink attachment to the drain? The reason I ask about a 4" pipe is because the distance from the new tub p-trap to the vent would be 82". which is too far for a 2" or 3" pipe. I hope you can understand the problem. Thanks so much for any help!

01-29-2005, 05:44 AM
No you can not use 4" for the tub drain, min size is 1-1/2" max is 2"

Distance from trap to vent depends on your code, here 1-1/2" is 3' 6" and 2" is 5', check your code.

There are other ways to accomplish this, not seeing the pipes and how your layout is, I can't explain to you what you might be able to do.

01-29-2005, 03:42 PM
Thanks for your input. Our code (CA) is the same as yours re: p-trap to vent distance. Would a 3" p-trap and drain be out of the question? I wish there were some way for me to better describe the situation . . . the master-bathroom being remodeled is on the 2nd floor, and the existing main drain and vent for the shower (north-east corner) in the master-bathroom is shared by the bathtub in the bathroom in the next room. The existing main drain piping is in the floor and wall shared by the two bathrooms (let's call it the east wall), and the reason I don't think the new bathtub drain can be attached to this existing one is because the floor space is not deep enough to attach a third wye or sanitary tee, there being two already attached to this main drain and vent (one from the exisitng master-bath shower and the other from the next-door tub.) Being able to run the new tub p-trap and drain to this joint would be the best solution because the distance would be 60" from the new tub p-trap to the existing vent. But since it there is no room for another joint, I thought we could run the new tub drain under the floor boards across the master-bathroom to the sink drain/vent (in the south wall), but the distance is about 80" and code would allow 5' or 6' from p-trap to vent for 2" and 3" pipes respectively. The new tub I want to install will sit against a common wall (north wall) with the neighboring house, and is adjacent to (to the west of) the shower stall; unless we add a false wall over this north wall (or somehow head off all the studs) to allow the pipes to run in front of the studs, I don't see any solution (not surprising, since I'm not a plumber!) Does this description help you see an alternative? Thanks -any advice would be greatly appreciated!

01-29-2005, 04:19 PM
The trap according to UPC section 1003.3 says, The size of a trap for a given fixture shall be sufficient to drain the fixture rapidly, but in no case less then nor more then 1 pipe size larger then given on table 7-4 the trap shall be the same size as the arm to which it is connected.

That being said, 2" is the max size, 3" is too large, why can't you run 2"

Why are you trying to run 3" to the tub, this makes no since to me.

If you need to access more area of the main for the connection, what is stopping you from doing so?

01-29-2005, 04:41 PM
Ideally I could run a 2" for the distance of five feet to the existing drain and vent, but I can't access more area of the main drain/vent for connection because I would have to access it at a point in the wall that is lower than the ceiling of the kitchen below - the slope of the new tub drain would have to slant steeply and cut through the ceiling to be able to drain the tub and access the main drain. Does this make sense? Right now, the entire "crawl space" length of the main drain is already accessed by the shower drain and the next door tub drain. How can I access the main drain below the level of the kitchen ceiling without the drain pipe cutting though the kitchen ceiling and wall? Thanks.

01-29-2005, 04:48 PM
Distance to vent on 2" is 5'

Run 2" and you should be fine.

Thats a drop of 2-1/4" at 1/4" per foot of drop, do you not have that much room?

Remember if you run 2" the make the trap size 2", reduce it to 1-1/2" at point where tub ties to trap.

01-29-2005, 05:22 PM
Thank you so much for your help - I'm sorry I can't seem to explain the problem - there is no free pipe length on the vertical part of the drain/vent (which is in the wall space) that lies at the level of the "crawl space" of the bathroom floor to attach new tub drain. I think you call this drain/vent a wet vent because the next room tub drains into it above where the master-bath shower drains into it. I would have to run the new tub drain to the wall space at the correct 2 1/4 slope, and then somehow turn it via a long sweep or closet bend and cut through a couple of studs to reach an area of this drain/vent pipe in the wall (below the "crawl space" level) to which I can attach a sanitary tee. Can you even have three fixtures (two tubs and a shower) fitted to a single drain/vent? I may have to call in a professional since I don't seem to understand the solution. Thanks again for your help.

01-29-2005, 06:51 PM
I guess I can't see this, pictures would be nice, sounds like you may need to call in help.

02-05-2005, 09:38 AM
Our handyman suggested we raise the floor about 6" where the new tub and shower will be so that the vertical drain pipe and be accessed to drain/vent the new tub - it works! My question is whether a 1 1/2" drain will be OK, even the though it will not conform to code because the distance is 4' 3" and the slope will be about 1 - 1 1/2" max? Thanks.