Venting Foiled by Framing! A New Approach...

[Lightningwill]

I was pretty sure I had a plan, but some tricky framing got in the way. Basically, for my master bath DWV, I can't land everything in the 9 1/2" joists in the way previously planned due to constraints on where I can drill some of the engineered lumber.

So I did some more brainstorming today and I'm pretty sure I have a solution (shown below). The biggest change vs. my previous idea is that the shower trap arm is now dry vented via a sanitee at the far end of the room (trap arm length is within spec). That sanitee drops directly into a 3" x 3" x 2" wye. The 3" input to the wye is a toilet drain.

The Question: Given that they both tie directly into an upright wye, is the vent on the shower sanitee adequate venting for the toilet as well?

Here's the relevant portion (12.8.4) of the 2015 NSPC: “For water closets and other fixtures that operate by siphonic action, the distance between the outlet of the fixture and its vent connection shall not exceed 3 feet vertically and 9 feet horizontally.”

If not, I'll upsize the lav drain to 2" to make it a wet vent, since it's too long if it's 1.5". But, I'd prefer to leave it at 1.5" if possible.

 

[Jeff H Young]

Id vent off double lavs . They let you run 2 lavs on 1 1/2 inch pipe? drilling Truss joists arent a problem follow spec. sheet

 

[Sponsor]

 

[Terry]

I've always done 2" for two lavs.

 

[Reach4]

Whatever size pipe you need, if you are worried about weakening the joist, you can convert to copper for the stretch being drilled into joists, you will minimize the required hole size. Adapt to plastic with shielded couplings.

 

[Lightningwill]

> They let you run 2 lavs on 1 1/2 inch pipe? drilling Truss joists arent a problem follow spec. sheet

It's not a truss joist/I-joist. It's an LVL header which has more restrictive drilling prohibitions. For my previous venting configuration, the size of the hole is not actually the problem. I was trying to wet vent the shower arm via the 2" wet vent and if I lowered the trap arm enough to get the 2" vent through the header in the middle third of its depth, the trap dropped below the plane of the ceiling.

> I've always done 2" for two lavs.

Good to know. Maybe I'll just do that and be done with it. Seems like I was okay on a DFU basis however. Each 1 1/4" lav would be 1 DFU and a 1 1/2" horizontal branch could take 3 DFUs according to NSPC.

 

[Jeff H Young]

Ligtning Will, yes LVL are much more restrictive. Cant you put a 3x2 y on near the closet bend and hit a wall with your toilet vent? I got to have a reason to run 1 1/2 inch even for one lav and I do that ocasionaly. samething with running copper ( reach 4 suggested) a smaller hole dont think thats a help on this job but a good option where you dont want to chew up too much wood

 

[Lightningwill]

> Cant you put a 3x2 y on near the closet bend and hit a wall with your toilet vent?

Yes, that's my other option (was actually figuring it would be a 3x3x1.5, but same principle). But since it seems like best practice is for the double lav to be a 2" anyway, and since it's in spec for a wet vent, that's probably the most straightforward.

Thanks everyone for the comments!