Need help planning out new bathroom DWV

[Europe72dead]

I’m renovating a bathroom on the 2nd floor and cannot use my existing 4” cast iron stack because there will be a window in its place on the 1st floor.

Please take a look at my iso drawings which show my tub and water closet wet vented by 2” through roof. The second photo provides a shared 2” dry vent that ties into the dry vent in my attic space before going through the roof. Is this overkill or needed? The 2” dry vent is dedicated to this bathroom.

The new 3” goes down into my basement and ties into my original 4” stack which will be cut 4’ from the floor.

Thanks!

 

[wwhitney]

Drawing #1 does not work, as for a horizontal wet vent, the dry vented fixture must be part of the upstream-most joint between fixtures, i.e. one of the two upstream-most fixtures. You have it connecting at the 2nd upstream most joint, making it fixture #3. The tub would require its own dry vent, which would then allow it to wet vent the WC. [Under the IPC, you could instead dry vent the WC and use it to wet vent the tub, but not under the UPC. NJ uses its own code, the NSPC, so you'd need to check it to know if that's an option or not.]

Drawing #2 does not work, as your dry vent needs to be connected to one of the two individual fixture drains, preferably the tub, as per the above discussion. Also, a wye rolled 45 degrees gives you a vent elevation of 30 degree about level; you'll need a 60 degree elbow to turn plumb. That doesn't meet the requirement of the vent takeoff rising vertically (which mean at least 45 degrees above level) until at least 6" above the fixture flood rim. Yet if the 30 degree slope section is only a foot or two, usually that is overlooked; I can't tell from your drawing quite how long it would be.

So your best options are to redirect the lav drain to join the tub drain first, then have the lav/tub join the WC; this would let the lav wet vent everything. Or to route the tub drain directly under the wall, where you can do the vent takeoff with a vertical wye or combo, then have the tub drain join the WC to wet vent it, and then bring the dry vented lav drain in.

Note that your tub trap arm is the pipe from the tub trap to the fitting where it is vented, either via a dry vent takeoff, or wet vented via joining a drain carrying a dry-vented bathroom fixture. This tub trap arm is limited to one pipe diameter of fall, i..e. 1.5" of fall if you use a 1.5" trap (a 2" trap also allowed). Which would give you a length limit of 6' if you pitch the tub trap arm at the minimum of 1/4" per foot (and a shorter length limit if you pitch it more). The NSPC may have a further length limit that is even shorter than you get from this computation.

Cheers< Wayne

 

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[Europe72dead]

Wayne, thanks, this is very helpful. Let me know your thoughts on this layout. The tub and WC are both on the same wall however the WC will be wall hung so I can’t put any additional pipe in that stud bay.

I’ve also included a layout of the floor plan.

Thanks!

 

[wwhitney]

That connectivity works, the dry vented tub can wet vent the WC. A combo is better than a san-tee on its back; you'll have to check whether the NSPC cares (the IPC allows a san-tee on its back, the UPC does not).

Also, the lav dry vent only needs to be 1-1/2"; the tub dry vent may or may not be allowed to be 1-1/2", you'd have to check the NSPC (the IPC would allow 1-1/2"; the UPC requires 2" because of the WC).

Cheers, Wayne

 

[Europe72dead]

Thanks Wayne, I can use a combo on its back instead of the san t.

One last question. I have a 2” VTR near where the tub dry vent would be coming into the attic (It currently vents the 3fl bathroom bathroom directly above this one). Can I tied my dry vent into that or should I stick with using the original VTR in my iso drawing? I’m not sure if it matters or not.

 

[wwhitney]

No need for another hole in the roof, you can tie the vents together at any elevation at least 6" above all the fixture flood rims.

Cheers, Wayne

 

[Europe72dead]

Great, if that’s the case, I’ll just tie both the lav and tub dry vents into the existing 2” attic vent. If an inspector has a problem it’s an easy fix. Thanks for all the help!

 

[Europe72dead]

One last consideration, if it’s easiest to run a wye with a street 45 off my main 3” run and then a long sweep 90 to get under the wall for my tub that would be perfectly alright as well correct? I will try to avoid the 90s but it might be much easier to run this way, I’m not certain yet.

See revision in red marker on the attached photo.

Thanks.

 

[wwhitney]

Yes, that's allowed.