DWV layout question for sunken tub

DWV layout question (with figures) for sunken tub

Hi everyone,

I have an older single story home on a raised foundation. Over the past 10+ years I've been replacing the old steel piping in the crawlspace under the house with equivalent ABS runs following the same DWV layout that existed previously. For example, in the remodel of the kids bathroom tub/shower I've utilized the previous standard stack layout as shown below



However, in the process of remodeling the master bathroom I've run across a difficulty with the existing layout. Unfortunately, the master bathroom is at the farthest end of house and I've reframed the bath as a sunken whirlpool. If I follow the above layout, I can not maintain the 3" main line run (approximatly 24 ft long) at 1/4 in/ft. I'm getting perhaps a 4.5" to 5" drop instead of the required 6".

So my question is: what can I do? Is a run sligtly less than 0.25 in/ft going to be a problem? My preference is to use the following layout but I've not seen it used elsewhere in my house. Does this violate plumbing code (UPC)?




Any comments are appreciated!

DWV layout question (with figures) for sunken tub

I'm hoping that by adding figures to show my situation it will be easier for folks to respond!
Please, any comments are appreciated.

Why aren't you putting the trap right UNDER the waste and overflow connection. Doing it your way you lose quite a bit of potential fall.

Hi hj, thanks for responding.

Although I could move the trap over, I don’t believe that would help. Perhaps I'm not understanding your thought. The real limitation is a girder holding the joists supporting the tub. The top of the 90 bend exiting the trap is touching the bottom of this girder in the figure. I’ll try to update the figure to show this. The length of the girder travels out of the page and essentially blocks access for routing a vent to the space between the joists on either side of the tub's waste connection.

So am I’m hearing that you wouldn’t recommend the layout that I suggested?

BTW, there is no overflow connection since the overflow will be a waterfall over the edge into the shower pan that is right next to the tub.

I`d like to see a picture of the water fall.

Here is a more accurate diagram of the solution I thought would be acceptable:



To install the standard stack layout it appears that I'd have to a drill 1.5" (or larger) hole through the girder for a horizontal vent into the space between the joists. Doing that might allow enough room to raise the trap and fit a med 90 underneath the girder. But I'm not sure if that would be structurally sound.

Is there a common sense reason why my layout is not advised?

cwhy2, I'm still in the rough-in stage so there is no waterfall yet. Actually the tub isn't even in yet, I was working the 3" main line when I ran into the height problem this weekend. I'll try to post some photos when it's done or once the walls and shower areas are floated.

From your drawing, I cannot visualize HOW the vent has any effect on how the drain slopes.

if I use the standard stack layout shown below, the vertical vent with san tee requires the use of a med 90 which brings the exit below my 3" main line (assuming I maintain a 0.25"/ft slope on it). The med 90 is not to scale in this diagram. In reality, I am only a couple of inches too low relative to the 3" line, but low nonetheless.

Why would you NOT use the original concept with a combo on its back?