Question on venting a single sink in a workshop/office.
I am trying to figure out the best way to vent this sink drain. It’s a 1.25″ drain, basically a small bathroom sink (there is no existing plumbing in the building).
I do NOT want to cut into the existing roof as it’s rolled roofing and 2/12 slope and fully adhered. I am not comfortable adding flashing on a roof of this type and will not be satisfied it wont leak.
The plumbing code is archaic to read. While I won’t be getting this inspected I do want to make sure I am following best practice. Coastal climate zone in BC, mild winters.
I plan to use a 1.5″ drain line in DWV pipe. 90 degree fitting off the back of the trap line running straight through the floor into a horizontal sloped drain.
This will ONLY be for washing hands, that’s it.
It looks like I should be able to run it to a dedicated french drain in the ground outside as its considered grey water?
What about venting? I do NOT want to go out the roof at all, I wouldn’t mind going out the wall but it appears that there is some rule about having no 90 degree fittings in a vent pipe so I don’t understand how one would go out the wall without using a 90 to exit. It also seems to say any vent has to go out the roof, but theres conditions for going out the wall that all seem to be superceded by rules about going out the roof? There is also a window within 3.5m of the only spot I could exit inside the wall cavity, I could run the vent back to the rear side of the building and exit there, but again, I would need to use 2x 90’s to make this happen.
Should I just use an air admittance valve instead of a vent at all? I would prefer not to cut into a bunch of drywall just to install a vent if I can just use a mechanical valve under the sink area to pull room air in the for the venting.
So basically two questions,
1. Can I use a french drain to receive the sink washing water
2. a. Do I have to use an actual vent line and if so, can that vent line pass out the wall instead of the roof? or b. Can I just use an air admittance valve instead of dealing with a dedicated vent at all?
Again, it is a workshop, with a single sink only used for washing hands. Thanks.
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Replies
You need to talk to your local code officials.
Generally, if you supply water to a building, they require a drain to the sanitary system. Because sooner or later someone will add a toilet to whatever drain you install. You can’t really blame then for being skeptical people try to play them every day to bend the rules.
In most locations air admittance valve is allowed only when a standard vent is impossible like a kitchen island and then only as a supplement to a normal vent.
Walta
OffGridForever,
Legally in BC the sink needs to run to an approved septic, or grey water system designed to treat the water. It can't just be run to an outdoor drain.
https://www2.gov.bc.ca/assets/gov/environment/waste-management/sewage/onsite-sewerage-systems/what_is_grey_water.pdf
And legally you can not use an AAV for any fixtures it is possible to vent.
Practically your plan should be fine. Vents don't care how many 90 degree turns there are as long as the pipe slopes, and they can exit from walls if you maintain the proper distance to operable windows and air intakes. It's an open question as to whether a single hand washing sink even needs venting.
The installation of a sink does not allow for an exception to the connection to a sanitary drainage system.
BC Plumbing Code allows AAVs "in situations where connection to a vent may not be practical"
However, sanitary building drains must have one vent that is minimum 3" in size. You will see why when the municipality blows out the mains.
If this "french drain" will be able to build positive pressure you really should vent. If not an AAV, or nothing, would probably work fine.
If this building has a crawl you could extend the horizontal run out to the back, or side of the building. Install a Tee where it exits with the branch for a vent line running straight up to above the roof. Plug the run with a cleanout. This setup will work with a full bath.
since the vent has to run above the roof line, I guess a couple of 45s would be acceptable to bump the top of the vent line out around the roof overhang? (12" overhang). This idea seems like it wouldnt be too much work. it does have a small crawl that I can use to run outside.. thanks for the idea
OffGrid-
It's not really answering your question, but have you considered a system with no hard plumbing? It seems like it would be a good option if your application is hand washing only, and also have venting and perhaps code challenges. Something along these lines or another on YT:
https://www.youtube.com/watch?v=YsH5WUAAD-8
I am honestly starting to consider just doing this considering the situation. The building also has no water line yet and I am not sure I want to trench the distance it would require to serve water. All things considered a jug of water with a small 12v pump (the building has batteries for power), with another water jug for water catchment so I can just dump it out in the garden might be the way to go, though I am still curious about a gray water system if its feasible.
OffGridForever,
Steve's suggestion makes sense to me too. It avoids a lot of work, and worries about code compliance. I'd be tempted to go that route.
Just as an added note, this property is in the sticks, with no sewer or water connections for miles. It is serviced by a well and has septic (but the septic is a LONG way away, and not practical to be attached). This is why im wondering about a gray water system.
I appreciate all the replies!
If you are really in the stick, you will never get inspected so do as you please. Run the water to a dry well extend the drain vent a few inches above the rim of the sink.
Walta