New home DWV design help?

[MikeD]

I'm designing a new home in Tucson AZ. IPC 2018. I've attached an isometric laying out how I was planning the DWV. About to submit for permit, but I'd really like an experienced plumber to look over it, as there are so many rules with wet vents etc, and there may very well be a better DWV layout. I've called over 20 plumbers, and so far ALL have said they either don't do new construction plumbing, or they're booked months out and aren't taking on any new work right now.

Note the building is unusual due to site constraints and a 'sawtooth' roof. I'm trying to limit vents through the roof to the one required, using AAVs elsewhere. The sawtooth roof covers most of the center of the building, which has solar panels on the south-facing slopes, clerestory windows to the north, and gutters in between for rain. So there's really not a good way to vent through that area. I combined bathroom groups into wet vents, and ran everything horizontally (my understanding is that's better for wet vents).

Please lmk if you see any issues. One thing I'm wondering is if there's a limited height for a vertical drop out of a toilet for instance before it sweeps horizontal. As you can see we've got some drops of almost 36" below finish floor (note the "X"s on the isometric represent the top and bottom of concrete slab/footing where pipes drop through vertically).

 

[wwhitney]

The resolution on the image is too low. Maybe you can provide a PDF?

Cheers, Wayne

 

[Sponsor]

 

[MikeD]

Higher resolution PDF attached. Also realized I had an extra, unnecessary AAV in the JPG iso, so removed that. Thanks.

 

[wwhitney]

A few issues on the right side:

- On the branch above the building drain, you have a lavatory without an AAV, that doesn't work. The upper lavatory can not wet vent the lower lavatory, as the vent connection for a trap has to be at an elevation no more than one pipe diameter below the trap outlet (WCs excluded).

- Your two showers there show some bends in the trap arm, with the isometric I can't quite tell if either of those bends are downward. Again, the horizontal connection to the 3" line that is wet venting the showers has to be at an elevation at most one pipe diameter (2") below the shower trap outlet.

- On the branch below the building drain, the order of fixtures in the bathroom group is wrong for horizontal wet venting. Since the lavatory is providing the vent, it has to be one of the two upstream-most fixtures. As you have it, the unvented WC is joining the unvented shower; but each fixture needs to be vented before or as (when horizontal wet venting) it joins with another fixture.

Cheers, Wayne

 

[MikeD]

Thank you @wwhitney! That's exactly the type of feedback I was looking for. Funny thing is I deleted that AAV thinking it was unnecessary because it could vent from the other. Just added it back. The 2 shower arms are just sloped at the typical 1/4"- they look weird because I was planning to bend those arms just a little so the long sweep fittings fit one right after the other (this perspective is slightly more vertical, so maybe illustrates that better). The drains are right in line with each other, and my understanding is they can't share the same branch arm- if they can, please let me know because I would have them share it and then add a cleanout to the right of them as well. I fixed the other bathroom group it so that only the toilet joins the wet vent upstream of the vent through roof (VTR). Please check that out and see what you think. No problem with the only VTR on the building being there? And no problem with ~36" vertical drops in some cases from toilets before the drain turns horizontal? Use a long sweep there? Anything you'd do differently? Thanks for all your help.

 

[wwhitney]

1) The two showers can combine before the 3" line only if you pull a vent off them before they hit the 3" line. That could be dry or an AAV. If they are being wet vented by the 3" line, they need to hit it separately.

2) My understanding of the IPC is that you just need one vent through the roof.

3) No problem with the initial 36" drop from the WC flange to the first bend, and you might as well use a long turn 90.

In the vicinity of the 3" vent through the roof, you can revent your sink vent takeoffs rather than use an AAV; that would be more standard. I take it with the sawtooth roof and I guess cathedral ceilings, there's no attic space for combining vents to a single roof penetration? And it's one story, so there's no second story floor joist system to combine vents in?

14 AAVs is alot. I can tell you that I think the layout meets the IPC rules. I don't have the experience to know if that will actually work well.

Cheers, Wayne

 

[MikeD]

Thanks again Wayne. Really appreciate you taking the time. Yes the showers (actually a freestanding tub and shower) are in the middle of a large open master bathroom, so they'll have to remain separate. That AAV near the VTR was a mistake courtesy of working late. I do intend to vent that one straight over to the VTR, no AAV. Correct on no attic at all (spraying foam insulation on bottom of roof deck between trusses & rafters) and cathedral ceilings over most of the structure- I attached a building section so you can see what's going on.

Thoughts on the AAVs: if they work well, I love the idea of fewer roof penetrations anyway, not only because of potential leak points, but because of energy efficiency (thermal bridging in the worst direction). I get that a passive vent is better because a mechanical is going to eventually fail, but seems like they're a cinch to replace if you can just screw on a new one. I can see it being a bigger issue if a homeowner doesn't know anything about plumbing or doesn't replace it if it starts to stick. Sounds like they're designed for decades of use and most don't fail early, but I'm going to make sure I keep a spare on hand so it's a 5-minute fix. I don't mind that rare hassle compared to the 24/7/365 benefits of long-term energy cost savings by not running a bunch of easy conduit for heating and cooling loss (& potential for leaking roof, animals nesting in vents etc). I never would have thought to do this were it not for the fact that the sawtooth roof area is completely covered by PV and gutters so it's especially difficult to run a VTR, but it kind of seems like a no-brainer to me now regardless.

Question: are you certain about the need for wet vented lavatories to vent to air vertically within 1 pipe diameter drop of the trap weir? My thinking is that from a physics standpoint they'd just need to be within 1 pipe diameter drop from where they turn horizontal (not counting the short horizontal run in the sink cabinet). If there were more than a 1 pipe diameter drop in the horizontal wet vent branch, that wet vent branch could totally fill with water and airlock/glug (or whatever is the right plumbing term So I can see a 1 pipe diameter requirement there, but don't see why it's necessary from the trap weir. Just my curious mind trying to figure it out.

 

[wwhitney]

Question: are you certain about the need for wet vented lavatories to vent to air vertically within 1 pipe diameter drop of the trap weir?

I don't follow your question, because you don't have any wet vented lavatories. Typically the only way to wet vent a lavatory is with side by side lavs; then you can have a common horizontal drain, with a dry vent takeoff between the two lavatories. That dry vents the upstream lav, and the downstream lav is wet vented.

Anyway, the general rule for venting is that any trap needs to have a vent come off at an elevation that is no more than one pipe diameter lower than the trap outlet. That vent could be a dry vent (taken off vertically and rising to roof or rising at least 4" to an AAV), or a vertical wet vent, or a horizontal wet vent.

Cheers, Wayne

 

[MikeD]

In the beginning of this thread you told me I had to add an AAV on one of the lavatories, and I'd said I'd just taken it out, since I thought that it could be wet vented by the other lavatory on the other side of the bathroom. Definitely not a problem to vent that one with an AAV too, but I was just wondering why the physics wouldn't work so long as the drop was less than 3" (one pipe diameter, so that there was an air path above any waste in that line). Not that important to explain it to me, I'm just curious. Thank you again for your help

 

[wwhitney]

As you drew it in the first diagram, each fixture drain for the two lavs drops down separately to the 3" line. That's not an allowable way to wet vent the second lav. If instead you have a horizontal drain that goes from one lav to the next, you can horizontally wet vent it as I described; then the combined drain can drop down to the 3" line.

Cheers, Wayne