I mocked things up in Google sketchup as best I could.
http://img855.imageshack.us/i/bathroomplumbing.jpg/

Overall, it looks like the following:

I'm in Massachusetts
Everything is 2" PVC, except the vent would be 1 1/2" (could be made 2" with some effort)
The laundry trap arm is within 6' of the vent as per 248 CMR 10.16(12): Table 1: Distance of Fixture Trap from Vent
The laundry standpipe will be ~40" above the base of the washer, couldn't find a minimum height off the floor for the trap though? (248 CMR 10.10(12.b.1.b)
The his & hers double lavatories have 1' 8" trap arms going to a double sanitary tee (make this a double wye instead?)
The tub trap arm is 6' 9" from the stack, I'd like to wet vent it, going up the exterior wall near the tub would be very hard to do. Going other directions are further and through joists.


I believe problems with the current layout is the laundry draining into the pipe the bathub cannot went vent due to the laundry discharging in that pipe AND the bathtub trap arm is 9" too long (6' max distance to vent).

a) I might be able to move the tub in 9", then extend the stack up under the medicine cabinet into a 90 across into the 1 1/2" vent. I'd be 12" higher than the highest flood rim off that vent at that point, so going horizontal is OK?

b) Or could I run a vent off the bath trap arm above it and run at a 1/4" slope up and come up near the existing stack then across at 42" high and tie in there? Would this be a horizontal vent, which can't be done unless I'm 6" above the flood rim?

If I did a) I'd still have to run a seperate drain for the washer. I think that would be very tight, even though I have double walls with 9" of space total (including the 2x4 wall plates). If I did that, I could come off that drain and under the left medicine cabinet then over to join the main vent?

If I did b), then I wouldn't have to worry about the laundry draining in with the others? Checking max fixture units for the 2" drain, I appear to be within spec.

Do I have an option c)?

Hi Joseph...

Your picture didn't post. Please try posting it again and I'll have a look at it for you, OK?

You are correct that you cannot wet vent a tub using a washing machine drain/vent.

Mark

Sorry about that, here's the picture
http://dorko.no-ip.com:8080/code/bathroomplumbing.jpg

Hi Joe...

With what you have presented I am afraid that all fixtures here will require individual vents... see drawing below.

You cannot wet vent the tub using the lavatory in this case because you have a washing machine on the drain line (like you thought). The only way to reduce the venting would be to take the lavatory drain by itself off the tub drain, but here, this isn't really worth it as the pipes as laid out is a better layout as you have it drawn up. The lavatory drains off the 2" drain should reduce to 1.5"... no need for 2" into the sinks. Increase the vent to 2"

You also need to add a vent to the washing machine drain. In my area, the inspectors want all washing machine drains individually vented... no exceptions. You may want to check with your local inspector as this is open to "interpretation" of the wet venting section of the code book. The standpipe out of the trap needs to be between 18" to 30".

On your 2" vertical to horizontal change in direction of waste pipe, make that a 2" long sweep elbow.

You could also reduce the tub drain to 1.5"...2" only required when underground. Here, as long as properly pitched and vented (vent must be within 5' of trap if 1.5") the 1.5" tub drain won't clog up in the drain pipe... usually only in the trap.

More questions? Let me know, OK?

Mark

Mark,
Thanks so much for your help, time and suggestions!

I modified your drawing to number fittings and their type & attached it. Would you mind doing one last review? I'm going with the pipe sizes you suggested.

You said "On your 2" vertical to horizontal change in direction of waste pipe, make that a 2" long sweep elbow." Do you mean #9 on my new drawing? If so, is this an above code suggestion/better performance? I believe code says quarter bend is OK there?

NAturally the #3 sanitary tee is oriented properly, but can a sanitary tee be used on its back for #6/12 as it is for venting only?

Thanks again!
Joe

At #8, the elbow can definitely be a regular 1/4 bend, but best is to use a long sweep if you can fit it... up to you here.

#9 and #7 can be the combo wye and 45 as you drew up, but #9 can also be a sanitary tee fitting.

Sanitary tees for vents only at #12 and #6 is perfect... ;)

Use 1/4 bend 90s for all vent elbows.

#2 and #4 should be 1/4 bend 90s... no need for long sweeps there as they are considered the "TRAP ARM".

#15 must be a long sweep 90 as indicated.

Don't forget to check with your local plumbing inspector on wet venting the washing machine with the lavatory drain/vent. If he allows this you can eliminate that extra vent. I would love to know what he said, too, OK?

Back to you...

Mark

Hi Mark. Just a question. At 6 and 12 your area allows san tees? Makes sense to me. In our area a vent off the top of a horizontal drain must connect though a wye 45 combo. San tees can only be used to tie in vert to horzontal vents above the highest flood level rim (six inches of course.) Im just asking because we used to be able to use san tees at 6 and 12, but they changed it. The way I see it, san tees are just fine here. Just confirming that is code in your area. Thanks.

Hi Lee...

In my area, as long as the sanitary tee is rolled above the centerline of the horizontal drain line, a sanitary tee fitting is acceptable for vents only.

Thanks for asking... ;)

Mark