tub shower combo drain/vent question
I'm contemplating options for a bathroom renovation and was hoping to get some advice about drain/venting requirements for one of the potential scenarios. While a significant chunk of the job will be DIY, I plan to contract with a licensed plumber for the actual drain/venting work.....not an area where I possess the necessary confidence/competence. I thought I'd seek some advice here first, simply so that my wife and I can narrow down our options.
The current bathroom is an en-suite in a bungalow. Drain, water, hydronic heating are all easily accessed from the 4 foot crawl underneath and happily, the people who built the house in 1976 met or surpassed the code of the day.....as I've discovered doing other reno's, they took no shortcuts with electrical, heating or plumbing.
The current bathroom has a shower-in-tub unit, WC and single lav. We are thinking about moving a non-bearing wall and stealing three feet from the bedroom to expand the bathroom so that we could install a separate tub and shower. One option is to install a linear combo tub/shower unit (the type where the tub and shower pan are side by side in an integrated 8 foot acrylic unit).
The question is whether the two drains off the unit (which are 27 inches apart) could share the same 1 1/2 inch trap and drain and 2 inch vent, or whether they need independent traps?
I believe I (or more accurately the plumber) still needs to extend the waste line by three feet, move the waste stack and the shared 2 inch vent (which currently vents the tub/shower and WC) at the top of the waste stack into the new wall, but sharing a trap would require one less drain line connection at the stack.
From a code perspective, I'm in Victoria BC, and for the record, it is raining.