New Bathroom Layout

[yogibear85]

Hi,

First time doing major plumbing so pardon any lack of terms. This is a 1930s house with 2x10 joists in a room . I am adding a bathroom to an existing room with permits pulled under IRC 2015.

I have approval for the following plumbing layout by the county but it is subject to site conditions and rough-in inspection so I can change it. I can put up to 6" holes in the 2x10 by using Metwood 2810HRs (already approved)

Currently I have a 3" vertical coming up that I wye off for the toilet before running at 45 degrees above the 4x10 duct to a joist bay over. From there I run a combi and a 3" line to the tub since the run from the trap is greater than the vent length for a 2" line and to get the right slope 1/8" to fit in the joist bay. I then continue on with a 3" line to the shower at 1/8" and then transition to a 2" going vertical to an attic vent with the lavs on a common vent to the attic vent.

Questions:
Can I use a long sweep 90 when I come over from the first join bay and head to the tub and then combi in the wet vent? Or does the wet vent need to be the primary line with the tub branched off?

Should I try to vent the tub (it is under a window) instead of wet venting it? Not sure I can get 6" above flood level before I have to offset.

The plumbing design seems fishy to me but I cannot place it...so would appreciate a third pair of eyes. (Had a plumber friend review it and said weird but fine)

Thanks and let me know if I am missing information.

 

[wwhitney]

How about something like the drawing below, where red is 3", blue is 2", and green is 1-1/2"? The circles represent risers above or below. And I didn't adjust your textual descriptions to match the proposed layout. Some comments:

The two lavs are common vented, but the trap arm from Lav2 to the dry vent is limited to 6' for a 1-1/2" trap. So I moved the dry vent takeoff closer to Lav2, as if the joists are 16" o.c. it was too far away at the corner you labeled 2" vertical.

If you change the tub to a 2" p-trap, then a 2" trap arm can be up to 8', and it is measured to the wye where it joins the shower/lavs.

The dry common vent for the lavs wet vents the shower, then the tub, then the WC. The 3" line needs to start where the tub and shower join, as the wet vent at that point is carrying 6 DFUs, too much for a 2" wet vent.

As to elevation, if your 2x10s are 9" tall, then your 2" lines near the WC have to be at least 3-1/2" from the bottom of the joists to the center line of drain. That would let you drill a 2-3/4" or 3" hole in the joist while keeping the edge of the hole 2" from the bottom of the joist. Then if the drain going up and down the page is 12' long (looks more like 8' to 10'), at 1/4" per foot the drain would be at an elevation of 6-1/2" from bottom of joist to center line, still within the joist bay. So I don't see any need for using 3" to allow a slope of 1/8" per foot.

Lastly, my drawing shows a 3" quarter bend, a 3" wye, and a 3x2x2 wye all in the joist bay by the WC. I think that may not actually fit in the available width, even at a 45. So you could extend the 3" line through one joist and move the 3x2x2 wye into the next joist bay. At which point you could easily make the drain running parallel to the joists a 3" line if you needed to for some reason.

Cheers, Wayne

 

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[yogibear85]

That is better, thanks! I knew something felt fishy.

Yeah I am going to move into the next joist bay since it does not fit.

Appreciate the help!