Two walk-in showers suggestion on how to do this

[David74]

Hi guys,here is a picture of my current project.Both showers will go to the 3" ABS to toilet and than down to the main stack.The toilet is vented with 2" going up to the roof.( right side of the photo ).
What i would to do is somehow tie both showers to the existing 2" vent to the left ( which starts here it doesn't vent anything else and also goes up to the roof).That vent goes under the floor joist and use to vent the old toilet.
How do i do this ?
Scenario 1.Do i need to run two separate pipes from each shower or can i somehow connect the vents from both showers under the joists and from there connect it under the floor to the main 2" vent going to the roof.What kind of fitting should i use ?
Scenario 2.Run the shower on the right direct to the 3"pipe without the current Y and just vent the seond shower to the left with existing 2" vent ,which could vent both showers )That would be the easier way.Will that work or will i have clogging problems down the road.
Thank you so much for your help.

 

[Jadnashua]

You can combine vents, but not under the floor. You need to vent each trap arm separately, then at 42" above the floor, you can then tie them together so you only need one pipe going further up. Failing that, when one shower drains during use, it is possible it will siphon the other one dry without it being properly vented.

What are you planning for waterproofing the showers? The prep is the crucial thing for a successful, long-term, trouble-free shower. The tile is what makes it pretty and provides a wear surface, but it should not leak before the tile is installed. Lots of ways to do this, but, it is in the fine details that differentiate a successful one from a failure. Looking good is nice, but bring back a saying from the last election - you can't put lipstick on a pig!

 

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[David74]

Thanks for the replay Jadnashua,i get the idea .In that case i will run a horizontal vent ,about 45 inches from the 1st Shower ( on the right of the Pic ) , and separate vent from the second shower ( left of the photo ) about 10 inches and will combine the two at at least 42" above the floor.
Is there a code ( California ) how long a horizontal vent can be till it goes vertically ?
As far as water proofing the shower I will use USG shower systems for both showers.I did install one of those on the first floor last year and so far its been good.They do come with their own waterproofing membrane ,pre slopped base ,etc...I like those better than Schulter for its flexibility in so many different ways.
Also another question on drain pipes slopping .I know you have to have a minimum of 1/4 slope per foot.
How do the pros do that ? Do they glue all pipes and fitting flat and than the raise one side with ties to achieve the slope ?
Or do they slope all the pipes and fittings as they go?

 

[Cool Blue Harley]

Where two vents converge, each such vent pipe shall rise to a point not less than 6 inches in height above the flood level rim of the fixture it serves before being connected to any other vent. Shower curbs must be a minimum of two inches, maximum of 9 inches. That means your vents can be combined somewhere between 8 and 15 inches depending on your finished shower curb height. This code has nothing to do with siphonage. It ensures that if there is a stoppage in an overflow condition, the waste from one fixture will not flow into the other fixtures via the vent.

 

[Cool Blue Harley]

In California, not more than one third of the total permitted length of the vent shall be installed in a horizontal position.

 

[Jadnashua]

The code says, 6" above the flood plane OR 42" above the floor, WHICHEVER IS HIGHER for combining vents.

For a 2" drain line, the maximum length of the trap arm is 60".

 

[Cool Blue Harley]

905.3 Vent Pipe Rise. Maybe different in New England but this is the California Code. Took it right out of the book. Transfered it as you read it above.

 

[Cool Blue Harley]

We adopt the UPC code, it is superseded by the California Code, which is then superseded by the San Francisco Amendments. What section are you quoting? I would like to read it.

 

[Jadnashua]

I just read the 2015 section on this, and unless I missed something, 6" above the flood plane of the fixtures using that vent is correct. Since the two showers will have a dedicated vent through the roof, that should suffice. Should someone ever try to tie something else into it, it could be problematic having it that low, and the 42" may be a more practical height in case something changes later.

Terry and the other plumbers on the site have been stating the requirement as I have, which may have been superseded or amended sometime in between where they followed that practice. The 42" comes from a typical kitchen countertop being 36" + 6", or the 42".

Would like to hear other pros, and the version of the code where this may have changed, or, if I've missed something.

 

[Terry]

We often mention 42" as a safe number to be at 6" above a flood level. The situation can vary depending on what you are plumbing for.
Some of the advice here is dumbed down to work in more places and jurisdictions. Somewhat generic.