Plumbing vs Framing

[orcas]

It seems to me that each profession develops standards in isolation from the others. My dilemma is fitting a shower drain between floors with 12 inch engineered wood I joists. While I can more or less have my merry way cutting holes in theI joist web, cutting the flange is out of bounds, leaving about 9 inches of vertical play. The 2 inch shower trap takes about 7 inches itself and if I put a 2 x 1 1/2 x 2 wye on the drain leg I've used all 9 inches.

From what I've read, a vent line must tie into the drain line above its midpoint, if I camber the y over 45 degrees I'm still about 9 inches tall. Also I understand that a vent cannot run horizontal until it's 6 inch above the rim of the drain it serves. With these limitations, I don't see how I can get the vent line anywhere without cutting the flange (the vent extension out of the wye eating up vertical rise). Even if I cut the flange, at 45 degrees I can't go far without penetrating the floor.

This drain is in a 36" x 60" shower, I've got the drain pushed within 6 inches of a wall and still can't get the vent to the wall and stay at 45 degrees. Neither the joist nor shower dimension s are that unusual, how is it done? Can I run a vent line at a 1/4 to 12 slope (like a drain line) below the rim and be ok?

Thanks for what help you can offer.

 

[Terry]

You can go five feet before you add the vent. Is there a wall nearby that you can put the vent in?

 

[Sponsor]

 

[hj]

I have a difficult time following your pipe routing, (cambering, Ys, etc.), so am not sure you are even doing it correctly.

 

[orcas]

Well, I've spoken to two plumbers in the flesh, not that I don't highly value the information shared here, and the answer from both is that it is impossible to fit a 2 inch p-trap plus a 2 x 1 1/2 x 2 wye and any sort of "vertical" vent run in the 9 inches of vertical play that a 12 inch engineered wood I joist offers. They both said they camber the wye so the vent comes into the drain at 45 degrees from vertical, that is the vent leg joins the drain line at at 2 o'clock or 10 o'clock angle rather than 12 o'clock, and run the vent at a "horizontal" (sloped as a drain line) to a long sweep 90 up a wall.

Both have had numerous inspections of this approach and passed, as there was no other practical way to do it with the limited vertical space available, particularly if one tries for a center drain. (I am not, although it would make tiling easier and a more comfortable shower floor to stand on.)

With this approach I will have about a 9 inch horizontal run in my vent pipe under the rim of the shower. If there is a better idea out there I would love to hear it, otherwise I think I will go with the above suggestion.

I should add that there are additional complications in that this shower is over a garage, so there are no interior walls below to accept a vertical run and the exterior walls are ICF's, again leaving no space to work with.

Thanks for your consideration.

 

[Dj2]

About the vent, what your plumbers recommend is the best you can do.