Re-routing tub drain horizontal one joist space

[FLN]

Hello, I've been a long time lurker on this most excellent forum - so much great advice! I'm in the throes of a master bath remodel, replacing one of those old built-in whirlpool units with a freestanding tub. This required me to move my 1 1/2 tub drain line over one joist space. Due to placement/etc., I went with short sweeps but now I'm having second thoughts.

Am I asking for trouble/should I redo with long sweeps, instead? this might jog my layout slightly (moving the drain an inch or two further away from the joist). Ugh.

I've found the aforementioned (in other posts) table 706.3 (uploaded) from the IPC that states that short sweeps can be used for waste less than 2" but of course I'm in Minnesota and they are now using 2020 UPC code with this opaque statement:

"Horizontal drainage lines connecting with other horizontal drainage lines shall enter through 45 degree (0.79 rad) wye branches, combination wye and one-eighth bend branches, or other approved fittings of equivalent sweep."

 

[wwhitney]

That statement means you need to use long turn 90s. But it would be better not to use two 90s at all.

First, where's the trap going to be, can you just turn the trap outlet by 90 degrees and eliminate one of the 90s?

Second, what's the big picture, literally, where's the other end of your trap arm and how does it connect? Under the UPC, you need to have your vent connection within 42" of the trap outlet.

Third, if neither of the above yields a layout change, what size is your joist, and can you drill the joist at 45 and use two 45s?

Cheers, Wayne

 

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[FLN]

That statement means you need to use long turn 90s. But it would be better not to use two 90s at all.

First, where's the trap going to be, can you just turn the trap outlet by 90 degrees and eliminate one of the 90s?

Second, what's the big picture, literally, where's the other end of your trap arm and how does it connect? Under the UPC, you need to have your vent connection within 42" of the trap outlet.

Third, if neither of the above yields a layout change, what size is your joist, and can you drill the joist at 45 and use two 45s?

Cheers, Wayne

Thanks for the reply.

I could certainly do two 45s if I drilled the joist at an angle. Wasn't sure if code would allow 45 degree hole in joist?
The vent is within about 16 inches of the first 90. The trap is about 6 inches from the second 90.
The joists are 2x10. Hole is < 1/3 of the width about 2 1/8 in diameter.

Cheers,
FLN

 

[wwhitney]

So go with option 1 in my post, eliminate one 90, and drill a new hole in the joist were required.

I take it that with this freestanding tub the waste and overflow are above the floor, and you just need to bring a single 1-1/2" line though the floor. Once you've located that, you can swing the u-bend of the p-trap through almost 360 degrees (pointing directly away from the joist doesn't work, as the tailpiece would block the trap arm). Pointing directly at the joist might get the trap elbow too close to the joist. Then based on your chosen approximate u-bend location (avoid perfectly parallel to the joist, as then you only have adjustability on only one side), pick a hole location, drill the joist, point the trap elbow outlet directly at the hole perpendicular to the joist, and use one long turn 90 on the other side of the joist.

Holes in a joist need to be 2" clear from other holes and from the top and bottom of the joist, and of maximum diameter 1/3 of the joist depth.

Cheers, Wayne

 

[FLN]

Your #1 could be my option - drill a new hole (will be about 3-4 inches from existing hole), use a single 90 long elbow - note the trap would have to be parallel to the joist - it's not clear why I should avoid this orientation, since this is the exact location where the 1 1/2 drain will come through, so no adjustment necessary. I was definitely overthinking the straight alignment of the trap making it a straight run!

Since I'm using a Jacuzzi floor drain, the drain is cemented to the trap and there is a "liner" inside with rubber gasget into which the brass downspout goes - and I am simply "aligning and dropping" the attached drain pipe into the hold - that is where the freestanding tub will go for the duration.

 

[wwhitney]

Your #1 could be my option - drill a new hole (will be about 3-4 inches from existing hole), use a single 90 long elbow - note the trap would have to be parallel to the joist

It would not have to be parallel. It can be at any angle that fits without the pipe hitting itself or the trap hitting the joists.

- it's not clear why I should avoid this orientation, since this is the exact location where the 1 1/2 drain will come through, so no adjustment necessary.

Because you are going to drill a hole in the floor, and drill a hole in the joist, and then glue up your trap. Drilling holes is imperfect, and If you shoot for the parallel orientation, and your holes are too far apart in the dimension parallel to the joist, you are out of luck (*). Whereas if you turn the trap 30-45 degrees towards or away from the joist, and your holes are slightly off either way, you can adjust the u-bend orientation to get everything to line up perfectly.

Cheers, Wayne

(*) Not really, you could put a 22-1/2 degree elbow in the trap arm, or enlarge the hole, but that would be annoying compared to just adjusting the u-bend.

 

[FLN]

Ah good points on alignment, etc.

Thanks for your help!

Cheers,
FLN