Venting a bathroom

Cossack

From my reading there are two methods to vent plumbing. There is the typical dry vent method that runs pipes slanted up which eventually attaches to a main waste pipe and vent outside. There is also a wet vent which I do not quite get. My bathroom is gutted and the unfinished size is a little more than 5’ x 8’. The main stack is against the 5’ wall. I want to place a small shower stall and a toilet next to each other and both fixtures will be within a few feet of the main stack. Am I correct in that I do not have to run any vent pipes up above for the toilet and shower because they will be wet vented?

On the other side of the bathroom 8’ over I will have a double sink and a wash machine just outside the bathroom. My plan on that side was to run one pipe to dry vent the sink and another for the wash machine. I would have them meet in the attack and connect them to an AAV instead of making a hole in the roof.

Does that sound good? Thanks in advance to all who answer.

Alan

Where are you located?

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Journeyman Plumber

The Engineer

You can only wet vent a toilet or shower through the sink drain, you can't wet vent the toilet through the tub, or the tub through the toilet since they both have sealed traps. It has to be wet vented through the sink drain which is then dry vented to the atmosphere. Also, the drain piping configuration from all three fixtures needs to be looked at to make sure its piped properly for air flow.

Cossack

Engineer:

Thank you for that explanation. So I am thinking I will have to vent the toilet and shower up into the attic and attach them to the Air Admittance Valve (AAV) along with the sinks and washing machine. Right?

I think what you mean about checking the pipes for proper air flow is that they are slanted UP toward the AAV. I think it is supposed to be ¼” per foot.

Cossack

Alan:

I am about 100 miles north of Detroit.

The Engineer

Depending on how its piped, you might be able to have a common vent for both fixtures and not have to vent each seperately. I really frown upon AAV's, they don't work as good as a vent that extends through the roof. An AAV allows air to enter the system, but it doesn't allow air to escape the system, so an AAV only does half the job a roof vent does.

When i was referring to airflow, I was refering to how the sink drain needs to connect to the toilet and tub drains at a certian location to allow airflow in the drainage line, not the vent line. You only have to pitch the vent pipe if its going through the roof to allow any residual rainwater to drain out of the vent, if your using an AAV, you don't really need to pitch the vent.

Cossack

I think you are referring to the rule that vents must go from vertical pipe to horizontal at least six inches above the highest fixture. According to my reading this means about 41”……Or do you mean something else entirely?

I am using the AAV to avoid another hole in the roof. My roof is steep and is on the second floor. I would rather not crawl out that far. Plus I am going to have to make some holes for an exhaust fan vent. Fortunately the fan vent holes will not be too far up the roof.

The Engineer

Does your main stack already extend up through the roof?

Cossack

Yes it does, but it is the old black iron type and I really do not want to have to cut into it. My attic is not exactly a good work environment and I have never done that type of work.

I have reasearched the AAVs and many say they are not a problem.

Alan

AAV's and their use vary from region to region. Around here they are not (specifically) prohibited, but our inspector will not allow them. Why? Well, because the code states that a vent must allow free air flow through the entire system. An AAV only lets air in, and not out. Therefore, it really doesn't qualify.

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Journeyman Plumber

Cossack

Ok, so to summarize I should ideally dry vent my toilet and shower along with the sinks and outside wash machine. The sink is a little less than eight feet away from the toilet and shower on the other side of the bathroom so what about the wet venting occurring through that? . The problem is that the bathroom is on the second floor and the joists underneath are 2 x 6 so I don’t have much room to work. The prior plumber cut away too much of one joist for the drain and I am not going to cut any more of that joist.

The house is very old and was built in 1863. I really just want to get this project done the easiest and cheapest way possible so I can move on to the other problems I have. Thanks again to all who answer.