How to run vent when drain pipe runs under bathtub?

[Whatnot]

I am installing a new bathtub and the drain has to run under the tub to the opposite end. I have not been able to find anything on how to run the vent with this configuration. I could run it up either end wall.

I only have 2x8 joists and am hoping to keep everything above the bottom if possible.

 

[wwhitney]

Do you want to run the drain down the joist bay to the opposite end and keep going horizontal with the drain past that wall above?

If so, per the Wisconsin plumbing code, you can use a 1-1/2" trap, run the trap arm at exactly 1/4" per foot, and have the vent connection up to 6' away when you use an upright horizontal combo for the vent takeoff. Or if you need more than 6', you could can use a 2" trap (upsize from 1-1/2" on the inlet side of the trap) and go up to 8'. The 1/4" per foot is critical here, as that is the minimum pitch, but the total fall is limited to one pipe diameter (hence 6' for 1-1/2" and 8' for 2").

If your drain turns downward where the vent comes off, then the Wisconsin plumbing code has lower limits on how long the trap arm can be, see Table Table 382.31−1 "Maximum Developed Length Between Vent and Trap."

Cheers, Wayne

 

[Sponsor]

 

[Jeff H Young]

2x2x1 1/2 combi on back 2x1 1/2 bushing on end with 1 1/2" p trap? pretty easy run pipe high in joist bay so trap dosent hang below joist in cieling below

 

[Jeff H Young]

btw you can come up on either end of a 5 ft tub with this method you can have the vent on the dran end or on the far side

 

[Whatnot]

The pipe it needs to tie into is a 2" running perpendicular to the joists. It is below the joists and running along the basement block wall so stepped in a ways from the above exterior wall. If I run the vent straight up, it will come through the floor under the tub. I do have the wall furred out so it might be possible to do but not easy.

 

[Whatnot]

Do you happen to have any diagrams of the combi on back? I am trying to picture that but can't see how there would be space for it.

 

[Jeff H Young]

The pipe it needs to tie into is a 2" running perpendicular to the joists. It is below the joists and running along the basement block wall so stepped in a ways from the above exterior wall. If I run the vent straight up, it will come through the floor under the tub. I do have the wall furred out so it might be possible to do but not easy.

Do you happen to have any diagrams of the combi on back? I am trying to picture that but can't see how there would be space for it.

well a little info helps. maybe notch down into the sill plate with a long sweep on top of that a 2 x 1 1/2x 1 1/2" spigot santee for the tub santee shouldnt be to high

 

[John Gayewski]

You need a diagram to illustrate your problem. With the pipe running perpendicular to the joists you should be able to vent between the joists and route a pipe through the back wall of the tub. Without some kind of spatial knowledge about what your dealing with the problem seems very simple to solve, but we'd need to know all of the variables.