Drain and vent question - Shower/Tub/Toilet

[DuncanG]

Hello all,

I'm trying to figure out how to plumb the drain lines for a bathroom I'm re-modelling, access is from the utility room in the basement below.

Originally there was a tub-shower combo with a 1-1/2" drain going to the 3" main stack via a sanitary tee that was right snug to the floor joists above. The tub drain didn't have a vent installed but was approximately 4' from the stack so maybe didn't need one? Below that the toilet is connected to the main stack with another sanitary tee. See this link for a picture.

I've added a separate shower and replaced the tub, toilet has stayed in same location, and now I need to figure out how to plumb the drains. See this link - in this picture the main stack is in the bottom left corner.

The original tub san-tee is right below the bottom of the joists and the toilet san-tee butts right up to it. How would you tackle this? Bonus question - how would you arrange venting for the tub and shower, assuming access to the main vent is unavailable.

 

[wwhitney]

The tub drain didn't have a vent installed but was approximately 4' from the stack so maybe didn't need one?

So what is draining into the stack above the tub san-tee? If nothing, or just the lav in the same bathroom, then the stack vents the tub (either dry or wet, respectively). That assume the total fall on the tub drain from trap to san-tee (the trap arm) is no more than one pipe diameter. If anything drains into the stack from a story about the tub, then the tub wasn't properly vented (unless the Ontario plumbing code is markedly different from US plumbing codes in that regard.)

As to adding the shower drain, if the tub is currently properly vented by the stack, then one obvious option is to drop the toilet san-tee and add a shower san-tee in between the tub san-tee and toilet san-tee. The toilet doesn't actually need to have a san-tee at the stack (the tub and shower do if the stack is providing the vent), so you could use a wye at the stack to keep the horizontal portion of the toilet fixture drain from being lowered. Or you could replace the tub san-tee with a san-tee with side inlet, just make sure the extra side inlet has the same curvature as a san-tee.

Cheers, Wayne

 

[Sponsor]

 

[DuncanG]

So what is draining into the stack above the tub san-tee?

Just the lav from the same bathroom. I kinda figured the original set up was just common/direct venting, glad to have confirmation of that.

Regarding moving the toilet san tee (or replacing with wye), the current tub tee and toilet tee are butted right up against each other. Any advice on how to deal with this and be able to put other fittings in there? I can barely squeeze a hacksaw blade in between the two right now, but once the cut is made there'll be no pipe to attach a fitting or a fernco to.

Also, if the drain line from the shower runs approx 7' across to the stack, it'll need a separate vent is that right? I have a partition wall between the tub and the shower that I can get into from below and install an AAV with an access hatch on the tub side (the tub is free standing) - sound okay?

 

[wwhitney]

1) If you want to rework those stack connections, and the stack both above and below the area you are changing is fixed vertically, then the common solution is this:

Cut out enough height so that the replacement portion can include pipe stubs at each end with at least, say, 2" of exposed pipe. Get (2) shielded rubber couplings rated for Schedule 40 to Schedule 40, e.g. Proflex 3005-33 for 3". Make the replacement portion about 3/8" shorter than the length of removed stack, that accounts for the rubber stop in each coupling plus a little extra wiggle room. Slide the rubber couplings onto the stack and slide the shields out of the way. Fold the open end of each rubber coupling back over itself so that only a little bit projects beyond the stop. Squeeze your replacement stack section in between couplings, unfold the rubber, slide the shield back into place, and torque to spec.

2) You need to check your plumbing code on allowable trap arm length. One of the US codes allows 8' for a 2" trap arm, which is the maximum you can get with at least 1/4" per foot slope while falling no more than one pipe diameter (to prevent siphoning); the other limits it to 5'. If you're allowed 8' and can get the slope exact, that would let the stack vent the shower.

Otherwise, yes, you'll have to pull a vent off the shower before the stack. That vent could reconnect to the stack at 6" above the flood rim of the lav (the highest fixture draining into the stack), or if your code allows it, connect to an accessible AAV that is at least 4" above the trap arm.

Cheers, Wayne