Can vent tie-in be lower than highest point in vent path to stack?

[Troutd0g]

I am adding a basement bathroom. The floor is structural (wood over metal joists) so I have good access to drain pipes beneath the floor. There are drain/vent stacks on opposite ends of the basement which serve the upper levels of the house - one on each side of the I-beam. The nearest stack is also the one on the near side of the beam (which is good) and it is 25 feet from the proposed bathroom. I want to combine the vent lines for toilet, shower, sink and route that vent along the ceiling and tie into the one of the 2 main stacks. The tie in point however will need to be lower than the highest point in that vent path. So the fixtures will vent up then across and then down about 2 ft. Is this permissible? Will it conform to code? Are there concerns about gasses being trapped or collecting due to this arrangement?

See my attached drawing.

Your expert opinion is GREATLY appreciated

Mark

 

[Jadnashua]

Not to code, will have problems...

You need to treat a vent line so it has the same slope as a drain line. There will be some condensation, and potentially precipitation that could accumulate in the pipe if it isn't properly sloped. The vent needs to be continuous so air can always move (vent) through it which is one reason why once a line becomes a drain, it cannot also be a vent.

Code wants the vent to go up until it is at least 6" above any line draining into it, or, in some cases, 42" above the floor of the highest drain fixture. Sometimes, that's easiest to make that connection in the attic.

 

[Sponsor]

 

[Troutd0g]

Not to code, will have problems...

You need to treat a vent line so it has the same slope as a drain line. There will be some condensation, and potentially precipitation that could accumulate in the pipe if it isn't properly sloped. The vent needs to be continuous so air can always move (vent) through it which is one reason why once a line becomes a drain, it cannot also be a vent.

Code wants the vent to go up until it is at least 6" above any line draining into it, or, in some cases, 42" above the floor of the highest drain fixture. Sometimes, that's easiest to make that connection in the attic.

In this case the vents will indeed rise far more than 6" above highest fixture in that vent loop (basement bathroom), but certainly every fixture in the upper floors will be higher.
I am a little confused by drawings that show venting to the main stack through multiple floors. It's almost like there needs to be a stack per floor.

 

[Jadnashua]

A drain is not a vent. Above a drain, the same pipe could be a vent.

 

[Xandrew245x]

I'm working on a bathroom in my basement right now as well, if the vent your wanting to tie into also serves drain fixtures on the floor above it, then you will not be able to connect to it below that. You would have to run the vent from the basement bathroom up to the first floor and go 6" above the drain fixture then tie into the vent. Connecting to the vent below the highest fixture would be wet venting which is against code. You will probably have to do what I am doing and run a new vent for the bathroom.

 

[Reach4]

I am a little confused by drawings that show venting to the main stack through multiple floors. It's almost like there needs to be a stack per floor.

Is there maybe a path through a plumbing wall behind a bathroom where you can run a new vent line to the attic?

 

[Jadnashua]

The only time you can wet vent something is within a single bathroom group on a single floor. Otherwise, once a line becomes a drain it CANNOT be a vent. IOW, if something drains into the pipe above, that line cannot be a vent for anything below that point (but can be above it). Now, did they do it differently years ago, yes, but we've learned what works better over time. Throw in bigger showers with multiple heads, washing machines upstairs near the bedrooms so you don't have to carry laundry up and down multiple flights of stairs, more bathrooms (one was considered a luxury when some of the plumbing was started), and to ensure things work properly...you need to follow today's rules. A high rise building gets complicated and can use some different rules, some of that dictated by the pipe sizes.

 

[Troutd0g]

Thanks for the detailed explanations - very helpful. It makes sense. Lesson to learn is to have a vent roughed in from basement to attic when having a house built. I didn't think about this when I had the home built. I knew with a structural basement floor I would have easy access to drain lines but was too naive about plumbing to realize that adding vent lines later would be pretty involved.

Adding a vent from basement to attic through 2 floors will be quite a job and require opening up walls on both levels to see where this can be accommodated.

If forego the full bath in the basement and ONLY do a sink for a kitchenette/wet-bar could I vent that sink with a studor/aav? The water heater emergency drain is vented that way in the basement now.

Mark

 

[Jadnashua]

Some places allow an AAV, some don't...you have to ask the building department or look it up (if you can find it) on your state and maybe county code listing.