Wet Vent Redux and other questions

[jba]

Hi All, first time posting here but I've learned so much just browsing as a non-member. Thanks to Terry Love for hosting this site! Hope I won't be banned for life after this extended post! . Can anyone firm-up my knowledge of wet venting, specifically in King Co. WA (Seattle)? I think I've learned the following:

• General idea: a pipe that drains another fixture can, under the right circumstances, have enough air flowing above any draining water to simultaneously serve as a vent for a fixture downstream.

• General Requirements:

* the section of pipe serving as a wet vent cannot be draining a toilet.
* the pipe serving as a wet vent must be sized correctly (i.e. large enough for the general idea above to actually work).
* the length of the wet vent section is not limited by code
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Of course I have a specific situation in mind, and related questions. In the attached diagram I would like to wet vent the floor drain, and maybe the toilet. All the pipe in the studio will be under a 4" concrete slab or embedded in the footing at the edge of this monolithic concrete pour, i.e. the 2" pipes for the laundry box and the sink run though the footing.

My specific questions are:
1. Is the 2" pipe shown sufficient to wet vent the floor drain? I think it is since I've read that a 2" pipe can wet vent 4 fixture units and the laundry box is just 2 units.

2. If I want to claim that the same pipe is wet venting the toilet as well, do I need to go up to 3" (since the toilet will add another 3 fixture units, bring the total to 5 units)? If so, when can that 3" be reduced to 2"? At the intersection with the laundry box dry vent I'm assuming.

3. The toilet is just about exactly 6' from the main 4" stack if I measure along the pipe path, closer as the crow flies. Should I just call it good for that vent? I guess that's probably inspector dependent, and yes, this is all permitted work will be inspected.

Thanks in advance for any help/advice!
Jonathan

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[Terry]

http://www.kingcounty.gov/depts/hea...ocuments/plumbing/horizontal-wet-venting.ashx

A lot of reading and pictures on this link.
The washer is not a bathroom fixture, so that's going to mess things up for you.

 

[Sponsor]

 

[hj]

1. The laundry flow is too great for it to be a "wet vent'.
2. same as above. It cannot wet vent the toilet either
3. The toilet is NOT the only thing on that pipe, so its distance from the main stack has NOTHING to do with whether it needs a vent or not, regardless of the distance.

 

[jba]

http://www.kingcounty.gov/depts/hea...ocuments/plumbing/horizontal-wet-venting.ashx

A lot of reading and pictures on this link.
The washer is not a bathroom fixture, so that's going to mess things up for you.

Thanks Terry, I'll check-out that info but it makes sense that the washing machine will disqualify this setup for wet venting. Doesn't every bathroom have a washing machine?

 

[jba]

1. The laundry flow is too great for it to be a "wet vent'.
2. same as above. It cannot wet vent the toilet either
3. The toilet is NOT the only thing on that pipe, so its distance from the main stack has NOTHING to do with whether it needs a vent or not, regardless of the distance.

Thanks HJ, I missed that detail on toilet-to-stack distance... didn't realize it had to be the only fixture on the pipe. Back to the drawing board!

 

[Terry]

Doesn't every bathroom have a washing machine?

Uh............No.
It is the wrinkle that gets you.

 

[jba]

After reworking my venting (added vent for floor drain) I'm considering these two options for venting the toilet. The heart of my question is that I don't understand how to account for/consider the part of the 3" drain between the toilet and vent in Option A that also serves other fixtures. Can someone explain that to me or point to a code reference? Is it just more wet venting and therefore a problem since I don't have a traditional bathroom group? Is Option B vastly superior? Option B will involve some concrete chipping, but is doable. Thanks!

 

[Cacher_Chick]

"A" fails to meet the most basic requirements.

It might help if you think of a vent for what it is- only the vent for that fixture. Each fixture trap on a drain must be vented, or it will be affected by the flow from the other fixture(s).

 

[FullySprinklered]

B works around here. A doesn't work anywhere. Unless you like suds boiling out of the toilet, that is.

 

[jba]

Thanks cacher_chick and fullysprinklered!