Bathroom addition venting help

[Bnewell101]

I'm adding a small bathroom addition to my house and I'm not sure the best way to set it up. Here is a rough sketch on what I came up with but I'm not 100% sure if it will work.
Any advice would be greatly appreciated.

 

[wwhitney]

- Your drawing is unclear, because sometimes you are using up/down the page to be mean vertical (the 2" vent, the stack), and sometimes you are using it to mean horizontal (presumably the sink and tub don't drain upwards). So how about a proper plan view drawing, where both directions are horizontal, and a vertical stack or vent is just represented by a circle, its cross section.

- How are the existing WC and tub vented? If the stack has no fixtures draining in from above, and the stack is the only vent, with the WC and tub drains combining together to before joining the stack, that's possibly OK. The IPC allows common venting like that; the tub trap arm from trap to stack (ignoring the WC) has to meet the usual rules, namely that it falls less than one trap diameter, while falling at a rate of at least 1/4" per foot.

- If the existing WC and tub are common vented, then you can't join your new drains into the stack at that level. Common venting is limited to 2 fixtures. You can join them into the stack at a lower elevation.

-The new bathroom sink will need a dry vent, as it has the highest elevation trap. The dry vented sink can wet vent the shower and the new WC.

Cheers, Wayne

 

[Sponsor]

 

[Jeff H Young]

looks to me like the 2 inch vent isn't needed and sink can wet vent Id use 2 inch if it was possible your code might allow 1 1/2 " I just don't use that size except trap arms or dry vents.
No consideration for tying into existing work as no info provided

 

[Bnewell101]

Sorry about that. I'll clear things up. I can't quite get a grasp on venting requirements so that was the main purpose of this post and I did the quick sketch for a response.
Sounds like there's more here than I bargained for (surprise surprise).

This is what my tie in point looks like. Left is from the shower, right is the toilet, then hit the stack in the back. I had hoped to just put a 3" tee wye in front of the 2" shower drain to connect the two 3". Below is ceiling to another room. Sounds like this may not be an option?

 

[Jeff H Young]

If the 2 inch line is independent of the venting for existing toilet then I see no problem. if its wet venting the existing water closet likely a problem with your plan. do you believe or can you get a view toward the water closet and see what might be vent between the 2 45s glued together and the closet bend? look down along the top of the 3 inch You can drive a truck thru the hole joist so I'm thinking good chance you can see get your head in there with a light

 

[Bnewell101]

if the 2 inch line is idepedant of the venting for existing toilet then I see no problem. if its wet venting the existing water closet likely a problem with your plan. do you belive or can you get a view toward the watercloset and see what might be vent bettween the 2 45s glued to gether and the closet bend? look down along the top of the 3 inch You can drive a truck thru the hole joist so im thinking good chance you can see get your head in there with a light

Right? Could have done a better job with an axe...

The shower has its own vent before tying in at the picture. The toilet doesn't

 

[wwhitney]

Right? Could have done a better job with an axe...

Yes, that joist needs some repair, which you should do while you have it opened up.

The shower has its own vent before tying in at the picture. The toilet doesn't

Ah, so that info is missing from the diagram in the OP.

No matter what, you need a dry vent at the new lav, but as you are under the IPC, that could be via an AAV, rather than a roof vent, if necessary. And then the new lav can wet vent the new shower and new WC. So the only real question is how to tie the new bathroom group into the existing stack while maintaining the venting of the current WC.

The simplest answer is that the IPC allows wet venting of two bathrooms at once. As long as you have drawn in all the fixtures on your diagram, you can just replace that WC LT90 made up of two 45s in your picture with a 3" combo, and bring your new bathroom group in on the straight inlet of the combo. The new lav will end up wet venting both WCs.

So assuming I understand your diagram in the OP properly, it's basically OK; the new vent just needs to move to the new lav trap arm, rather than be on the new shower trap arm.

Cheers, Wayne

 

[Bnewell101]

Yes, that joist needs some repair, which you should do while you have it opened up.

Ah, so that info is missing from the diagram in the OP.

No matter what, you need a dry vent at the new lav, but as you are under the IPC, that could be via an AAV, rather than a roof vent, if necessary. And then the new lav can wet vent the new shower and new WC. So the only real question is how to tie the new bathroom group into the existing stack while maintaining the venting of the current WC.

The simplest answer is that the IPC allows wet venting of two bathrooms at once. As long as you have drawn in all the fixtures on your diagram, you can just replace that WC LT90 made up of two 45s in your picture with a 3" combo, and bring your new bathroom group in on the straight inlet of the combo. The new lav will end up wet venting both WCs.

So assuming I understand your diagram in the OP properly, it's basically OK; the new vent just needs to move to the new lav trap arm, rather than be on the new shower trap arm.

Cheers, Wayne

Yes I basically left the back end out of the original drawing as I was focused on the addition.
I like to make things complicated I guess...

Since there was more to this than I expected I went ahead and dug up all the way back to the tub to make sure. Looks like the lav for the existing bathroom ties in to the trap arm for that tub but also has its own vent tying in to the stack pictured.
I don't imagine this being an issue since it also has its own vent correct?

 

[wwhitney]

Since there was more to this than I expected I went ahead and dug up all the way back to the tub to make sure. Looks like the lav for the existing bathroom ties in to the trap arm for that tub but also has its own vent tying in to the stack pictured.
I don't imagine this being an issue since it also has its own vent correct?

A proper diagram would help. But if the following are all true, you can proceed with your original drawing, where the new 2" vent should instead be a 1-1/2" (minimum) vent on the new lav trap arm:

1) There's no drainage attached to the stack above this floor, the stack goes through the roof and possibly has some other dry vents joined in.
2) On this floor, there are just two stack connections: at least 6" above the lav flood rim, a dry vent for the lav; and the bathroom branch drain shown in your picture.
3) The lav trap arm has a dry vent connected to it before it falls more than one trap diameter, which dry vent rises and connects to the stack.
4) The lav drain goes on to connect to the tub trap arm, again before the tub trap arm has fallen more than one trap diameter, and thereby wet vents tub.
5) The only other DWV connected to the stack on this floor is per your photo.

Cheers, Wayne

 

[Bnewell101]

I appreciate the help on this.
Sorry to complicate things, I drew up a new sketch which hopefully captures everything.
I went through and checked my conditions and it looks like I am too long of a run to vent the lav where I want with 1-1/2. If I up the lav drain to 2" that gives me 5' of run before I need to vent correct? Would this layout work?

 

[wwhitney]

The vent in your drawing is in the wrong place:

The drain coming out of a trap is horizontal. The vent for that trap has to connect to that horizontal drain near the trap elevation, in particular before the drain falls one pipe diameter. This prevents siphoning of the trap. So the trap for the lav will come off in the wall behind the lav, not in the floor below. You need a dry vent (to the roof or to an AAV) at that location (an AAV could be in the cabinet under the lav).

Once you have that dry vent, if your shower trap arm (drain from the shower trap to the wye where it meets the lav drain) falls less than 2", then the dry vented lav will wet vent the shower. And it can go on to wet vent the WC.

Also, you're under the IPC, not the UPC, so a 1-1/2" trap is allowed to have the vent up to 6' away, if the drain is falling at exactly 1/4" per foot: 1/4" per foot * 6' = 1-1/2" fall, the max allowable. Likewise a 2" trap could have a trap arm up to 8' long.

Cheers, Wayne