Venting Bathroom Under Roof Deck?

[Justintime]

Been lurking on here for YEARS, time to get some advice, hopefully!

Getting right down to it:

1. I have an add-on space under a second story roof deck
2. I want to turn it into a bathroom
3. I cannot use AAV, has to have actual venting (I'm challenging this currently)
4. I'm looking for proposals to place venting
5. I prefer not using the outside of the addition wall, as there is 4x10 bracing for the porch I don't want to drill through (see left upper of first image below)

As I see it, the simplest answer is to tie the washer, shower, and toilet into a wet vent. From there, I have two options:
1. run the vent up the inside of the exterior wall of the house. I'll have to tear out the interior side of the wall all the way up to the crawl space and go through the top plate and second story bottom plate. This will place the vent **very close to the roof edge**
2. the second option is punching into an interior second story wall you can see under option 2, this will set the vent back from the roof edge, but I may need to go through multiple floor joists. See the picture of the wall below.

Any thoughts or feedback on these two proposals? Probably looking at 1.5" vent pipe from the lav, then 2" pipe from the washer all the way to the roof.

Thank you in advance!!!

==========================================================


Here's the space:

==========================================================


Option 1:

==========================================================


Option 2:

 

[John Gayewski]

From your drawing none of those will work drainage wise. The washer needs to drain downstream from the bathroom group.

 

[Sponsor]

 

[wwhitney]

To expand on that, the washer standpipe will need its own dry vent takeoff, which can combine with the lav dry vent at any elevation at last 6" above both flood rims.

Also, since Idaho uses the UPC, for the lav to wet vent both the shower and WC, the drain connectivity, starting at the lav and going downstream, has to be:

2" lav dry vent -- 2" lav drain -- 2" shower drain joins first -- 3" WC drain joins next -- 2" washer standpipe joins last.

The shower drain trap arm, from the trap to the wye where the it joins the lav, is subject to the usual rules--maximum 60" length and maximum 2" fall, minimum slope of 1/4" per foot.

Cheers, Wayne

 

[Justintime]

What about this layout: Wet vent the WC from the lav into a 3", the shower and and washer standpipe connect into a 3" and are separately vented and the two 3" drains connect together and then go to the main sewer stack under the house. All 2" vents/revents merge into one 2" vent up to the roof via the interior wall?

This project is complicated by the fact that I can't run vent up into the crawl space along the long exterior wall because of the porch header/beam from the original porch seen in picture 2. Then the fact it's a roof deck.

I'm trying to get a vent pipe into that wall above the stairway. There's an L shaped office I think I can get into. But that means the entire bathroom unit + washer standpipe will be going into a 2" vent. DFU calculation works out.

Any concerns with this plan or alternative ideas?

 

[wwhitney]

The total aggregate vent area through the roof needs to be at least the same as a 3" vent. So when you combine your (3) 2" vents, you need to make the combined vent 3" and run 3" out through the roof.

Also, the lav dry vent needs to be 2" (as it wet vents the WC), but either the washer or the shower vent could be 1.5". But not both, as 1.5" pipe + 1.5" pipe + 2" pipe < 3" pipe, while 1.5" pipe + 2" pipe + 2" pipe > 3" pipe.

The WC needs to be wet vented within 6' from closet flange. That distance is measured from the closet flange, along the pipe run (including the vertical portion) to the wye where the lav drain joins it.

Otherwise, the drawing looks fine for venting. I didn't review the earlier part of the thread or look at the photos or drainage routing.

Cheers, Wayne

 

[Justintime]

Also, the lav dry vent needs to be 2" (as it wet vents the WC), but either the washer or the shower vent could be 1.5". But not both, as 1.5" pipe + 1.5" pipe + 2" pipe < 3" pipe, while 1.5" pipe + 2" pipe + 2" pipe > 3" pipe.

Got it, so close... So there's no way to get less than a 3" pipe through the roof, huh? That wall is non-load bearing that I want to go up through, so I can go through the entire bottom/top plate if needed, but getting it between the top plate of the 1st story exterior wall (see circle in picture) and the decking ledger board is going to require some cutting.

Would you mind just taking a quick peek at this drain diagram? I'm realizing now I don't need the fancy cleanout where the lav drain starts, I can just put it directly into the 3" WC drain. otherwise does it look kosher for UPC?

 

[Justintime]

I'll use this if we must use 3" vent.

 

[wwhitney]

On the drains, the combined washer/shower drain could be 2". IIRC 2" horizontal is good for 8 DFUs, and a shower is 2 DFU, a washer is 3 DFU.

The shower drain routing looks like you're going to use a san-tee under the floor for the vent take-off and then a LT90 to go back horizontal. That's fine if you can afford the drop, particularly if you need the flexibility to make arbitrary angle turns in plan. If you'd prefer to avoid the drop, and can move the vent takeoff to the right within that wall segment, there are other vent takeoff options available besides a san-tee.

My only other comment is to check the angles between the horizontal drains, you have a lot of angles that seem not to be the 45 degrees given by a wye. Which is an issue if all the horizontal segments are to be in the same plane (roughly, given the 2% drop on each line).

On the 3" vent requirement, that's assuming you're showing all the drains in the house (if you've said otherwise earlier, I've forgotten and didn't go back to read). If you have other vents through the roof, then they count towards the aggregate area requirement. Everything you've shown could be vented on a single 2" vent otherwise.

Here's the relevant section of the UPC as adopted in CA, since the OR version doesn't seem to be available at the same source:

Chapter 9 Vents: Vents, California Plumbing Code 2022 | UpCodes

UpCodes offers a consolidated resource of construction and building code grouped by jurisdiction

up.codes

Cheers, Wayne

 

[Justintime]

This is all gold clarification, thanks Wayne.

On the drains, the combined washer/shower drain could be 2". IIRC 2" horizontal is good for 8 DFUs, and a shower is 2 DFU, a washer is 3 DFU.

I see that, I was seeing that for IPC (we use UPC) a washer must terminate into a minimum 3" drain after the 2" washer fixture pipe. To reduce any change of shower backup issues, I was just gonna upsize to 3" at the combination of the shower and washer fixture drains.

The shower drain routing looks like you're going to use a san-tee under the floor for the vent take-off and then a LT90 to go back horizontal. That's fine if you can afford the drop, particularly if you need the flexibility to make arbitrary angle turns in plan. If you'd prefer to avoid the drop, and can move the vent takeoff to the right within that wall segment, there are other vent takeoff options available besides a san-tee.

Everything here you said is correctly assumed. I like your idea of moving it to the right to avoid drop if needed. I can put a 2x2 combo there instead

My only other comment is to check the angles between the horizontal drains, you have a lot of angles that seem not to be the 45 degrees given by a wye. Which is an issue if all the horizontal segments are to be in the same plane (roughly, given the 2% drop on each line).

Yes, they'll all be 45 degree wye when in plane. Should have written that out before I email this plan for my inspector to review. I'll write in the angles.

On the 3" vent requirement, that's assuming you're showing all the drains in the house (if you've said otherwise earlier, I've forgotten and didn't go back to read). If you have other vents through the roof, then they count towards the aggregate area requirement. Everything you've shown could be vented on a single 2" vent otherwise.

I have a main stack located in the center of the house. See where the blue line terminates on the picture below. It appears then that I can use a 2" vent and either:

1. Revent it to the main stack vent in the attic, or
2. Send it straight up the roof as proposed

Does that sound correct?

 

[wwhitney]

On the last question, yes.

Cheers, Wayne