I am in the process of installing DWV for a 2nd floor bath and kitchen sink in a garage at a summer home. My main question is in regards to what I have to do relative to venting the main stack, i.e. run a separate dry vent off or can I use a wet vent.

Details:

City sewer: 4" PVC
Main stack: 4" PVC
Vent stack: 3" PVC
Main waste: 3" PVC
4 fixtures: Bath sink, toilet, tub, & small kitchen sink on common wet wall

The vent stack is 3" PVC and is in the center of the 2nd floor of the garage and thus does not connect directly to the main waste stack which is located against a side garage wall. The main waste stack is 4" PVC and I plan transitioning it to 3" and then into a 90 degree sweep elbow. The sweep elbow will be at approximately 9' (Garage has 10' ceiling). A 4 foot long horizontal run of 3" PVC will then connect to two 45 degree elbows to get the horizontal waste pipe up into the web truss joist. (The jockeying is due to getting around a heat duct and up into the truss area so the garage ceiling can be insulated and drywalled, thus keeping the majority of the DWV pipes in the insulated/heated area.) The horizontal waste line then runs approximately for a length of 8 foot where it will pick up the wastes for the 2nd floor fixtures and the main 3" vent to the roof.

Starting from the main stack, the order of the fixtures / connections will be:
1) 2" Bathroom sink
2) 2" Kitchen sink
3) 3" Toilet
4) 3" Vent to roof
5) 2" Tub vent
6) 2" Tub drain
7) 3" Cleanout

The attached diagram also indicates that the vents for the 2 sinks and tub all tie into the 3" primary vent inside the common wet wall. I was planning on tying the 3" main vent into the 3" horizontal waste behind the toilet.

Questions:
1) Can the 3" main vent be connected to the 3" horizontal waste and provide the necessary vent for the main waste line or do I have to run a separate but parallel dry vent from the 3" main vent to the vertical main waste line and tie it it via a tee?
2) If I need a separate dry vent line, can it be 2" and how low can I connect it into the 3" main vent? i.e. can it be tee'd in below the 2nd story floor?
2) I think I remember that there may be a issue with tying a fixture (in my case, the tub)into a horizontal waste line after a toilet ties into the waste line. Is there such a restriction, that the toilet either has to be first or last feed into a horizontal waste line?

Thank you

Hi BLL:

My picture won't load... (of course not... right..? )

Anyway... a few changes.. ok?

First most looks real good...

I would end the run of horizontal 3" with a wye and 90 into the toilet (end cleanout in end of wye on RUN of the fitting).

Then install a 3"x2" wye behind toilet to pick up tub...this must be 2" full size waste and vent all the way to the 3" vent stack...this 2" tub vent will act as a wet vent for the toilet.

After 3" x2" wye for tub, install the 3" combination wye/(1/8th) to pick up the 3" stack.

Then install 3"x2" wye for kitchen sink... plan on leaving full size 2" dandy cleanout (see pic.) under kitchen sink (required by code)...Only need 1.5" vent for kitchen sink

Then install 3"x2" wye for bathroom sink... only need 1.5" vent.

Hang pipes every 4 feet..should have a riser clamp (see pic.) on the 3" vent stack as support.

That should get you started. Let me know if was not clear on anything... Mark

If this was helpful, please RATE THIS ANSWER. Thank you.

.

Mark,

Thank you for your reply.

The attachment was a pdf file. I have sometimes had trouble opening a pdf file automatically with Acrobat Reader and have found that I sometimes have to start Acrobat Reader before downloading the pdf file. Another trick is download the file and then open it with Acrobat Reader. Hopefully, you will be able to view the diagram.

The 4" main stack is already roughed in, as are the the 3" vent stack and the three 2" revents from the 2 sinks and the tub. Even though I could have used 1.5" for the 2 sink revents, since I used 2" for the sink drains, I just kept it simple and used 2" for the sink revents. Plumbing out in the middle of nowhere is quite different than in a large metropolitan area - 2 hour trip to the nearest supply house/store! I essentially am at the point of connecting all of the existing wet wall rough in piping to the main stack.

I was not aware about the dandy cleanout in the kitchen sink drain. I can not say that I have seen this in new construction in the Cook County Chicago area. I will have to look for it, as it implies that another hole has to be created in the back of the sink base cabinet to access the cleanout cap which would be set back inside the stud wall.

If you are able to view the diagram, I think I am close to what you described. I think the order may be a little different that what you described. From the cleanout at the end of the 3" horizontal waste line, the sequence would 3"x2" wye for tub drain (with 2" tub vent tee'd into horizontal 2" tub drain, then 3"x3" wye for vent stack, then 3"x3" wye for toilet, then 3"x2" wye for kitchen sink, followed by 3"x2" wye for bathroom sink.

Since you did not mention anything about having the toilet in the middle of the tub and sink connections, I assume that that there is not a problem.

You also did not mention any need for running a separate vent line down to vertical main waste stack, so I assume that the 3" vent stack connection along with the other wet vents will be sufficient and there will not be any code issues.

Since the horizontal waste pipe runs perpendicular to the web truss joist that are set on 19.2" centers, there will not be a problem with providing support every 4 ft.

If my playback is not correct, please let me know.

Thank you for you time,
Rich

Hi BLL... I was able to view your attached image, just could not upload mine last night.

The cleanout under kitchen sink only needs to be a full size 2" cleanout under the sink, so could also accomplish this with a union type ptrap (2" full size union trap, then bush down to 1.5" for sink) or an end cleanout in a wye fitting or similar. I just like the 2" DCO.

I did mention something about the vent/tub connections into main line.. I suggested that I would end the run of horizontal 3" with a wye fitting and off the wye branch install 90 directly into toilet (end cleanout in end of wye on RUN of the fitting). Do not trap the toilet (toilet has integral trap).

Then install a 3"x2" wye behind toilet to pick up tub... this must be 2" full size waste and vent all the way to the 3" vent stack... this 2" tub vent will act as a wet vent for the toilet. After 3" x2" wye for tub, install the 3" combination wye/(1/8th) (or wye and street 45)to pick up the 3" stack.

So, toilet ends the run, then tub , then vent stack, etc.

Those are the changes I would make.

The 2" vents are fine. Let me know if need more... Mark

Mark,

I have created an additional drawing to help clarify what you are proposing.

" --- So, toilet ends the run, then tub , then vent stack, etc."

Physically, the bathroom wet wall and the horizontal waste line are parallel to each other and the wet wall is almost centered above the waste line. The latest pdf should help show this. Since the toilet physical placement is downstream of the tub and 3" vent stack, I would have to do a bunch of crisscross connections to get the toilet at the end of waste pipe per your proposal. I am concerned that the toilet connection would need more bends to get back to the last wye and to avoid collision with the tub drain connections, and that the additional bends would pose an increased chance of a clog.

As a matter of best practice, I was trying to keep the number of bends in the toilet connection to the least number possible and the length the shortest in order to eliminate potential problems with the toilet waste line getting clogged from too many bends.

I may not understand why you want the toilet to be the last connection/wye. With the the 3" vent stack connection close to the toilet wye and the other 3 vents on either side of the toilet connection, I would have thought I was good.

With my 2nd diagram of the physical layout, does it change your recommendation?

Thanks,
Rich

OK.,. I think I got my pic. To upload... finally. It is so hard to talk plumbing layout without a picture back at you... ;)

Now that I reviewed your second pic... (throw that away.. ok? :) ) I see the vent stack is the better way to end the run. Look at my pic... see what you think.

Any questions let me know... Mark

Mark,

Looks good. Major difference from your most recent diagram is take the tub drain and vent off the toilet connection instead of making the tub drain/vent a separate connection to the horizontal waste line. The major difference I see is that you get a vent into the toilet waste line. I will see if I can make it work through the web truss joist.

I probably should use a 3"x2" wye instead of a 3"x2" sanitary tee to make sure there is no chance of the toilet waste getting hung up at the junction.

I am relieved to hear that I do not need to run a separate dry vent down to main vertical waste stack.

Hopefully I will be able to get most if not all of this plumped this weekend. Will let you know how it goes.

Thank you for your assistance,
Rich

Exactly Rich!

You understood perfectly.

Look forward to update... Mark.