Shower drain in 2x6 joists.

[SeaDave]

Terry,

Thanks for the guidance you provide.

Helping my son build a primary bedroom suite in his attic. It is engineered with 2x6 joists 8”oc for head height. Trying to fit a 2”shower drain trap in this space is challenging. I have a 2x6 plumbing wall, 1 joist away and would like to elbow into that space before connecting the trap then waste and vent lines in that wall space. Is this permitted? I was thinking of drain to 90, (long sweep required here?) then pipe through joist and 90 to trap then sanitary tee.

Thanks again!

SeaDave

 

[wwhitney]

As to going through the joist, you would need to get that engineered, as the largest hole you can prescriptively make in a 2x6 joist is 1.5". [D/3 is 1.83", but the hole needs to be 2" clear from the top and bottom, so that leaves only the central 1.5".]

However, the joist you need to go through, you may just be able to move it to be against one of the joists on either side, creating a 13" wide joist bay. Then you hopefully wouldn't need to go through a joist. [When I did something similar recently, I used doubled joists at 16" o.c. so as to have 13" wide joist bays, rather than 6.5" wide joist bays.]

If you do have to go through a joist, what's the upside to doing so before the trap, rather than after the trap?

Cheers, Wayne

 

[Sponsor]

 

[SeaDave]

As to going through the joist, you would need to get that engineered, as the largest hole you can prescriptively make in a 2x6 joist is 1.5". [D/3 is 1.83", but the hole needs to be 2" clear from the top and bottom, so that leaves only the central 1.5".]

However, the joist you need to go through, you may just be able to move it to be against one of the joists on either side, creating a 13" wide joist bay. Then you hopefully wouldn't need to go through a joist. [When I did something similar recently, I used doubled joists at 16" o.c. so as to have 13" wide joist bays, rather than 6.5" wide joist bays.]

If you do have to go through a joist, what's the upside to doing so before the trap, rather than after the trap?

Cheers, Wayne

Thanks Wayne,

My son is a licensed structural engineer and has cleared passage through this joist as needed. If I put the trap in the joist bay, I don’t have the vertical clearance for a 2” trap which is code here for a shower. The top of the trap outlet is nearly 1” above the top of the joist. If I go through the joist first, (essentially like a horizontal arm under a double kitchen sink) I can make a hole in the middle of the joist then add the trap in the plumbing wall where I have the vertical clearance. I could also notch the bottom of the joist and run the bottom of the trap under it, but that limits the location of the drain.

SeaDave

 

[Jadnashua]

The longer the pipe from the drain to the trap, them more surface area there is for soap scum, dead skin cells, hair, etc. to accumulate on the pipe walls. So, it could end up smelling easier than having the trap directly below the drain so the water falls faster vertically, rather than having to run horizontally, which will slow it down with less scouring.

 

[wwhitney]

I do see that the smallest 2" trap available is 4-9/16" from center line of bottom of U bend to centerline of outlet, or 7" from bottom of U bend to top of outlet hub (where I guessed the hub adds 1/16" to the radius).

I'm unclear on this plumbing wall--is it a wall above, meaning your shower must have its drain at the edge (e.g. a linear drain), or a wall that happens to be below, meaning you can let the trap penetrate that wall's top plate?

As Jim says, having other than a straight vertical tailpiece between drain and trap has some negatives, so there's probably a better alternative. Which is why I'm asking about the above.

If the wall is below, and you are using a centered shower drain, seems to me it would be worth moving the drain off center (with a custom pan if required) to allow a vertical tailpiece.

If all else fails, I'm not aware of a prohibition on adding the horizontal offset to the fixture tailpiece before the trap. You'd want a LT90 to go from vertical to horizontal, and then a medium 90 (or LT90) to go from horizontal to vertical for the trap.

Cheers, Wayne

 

[SeaDave]

I do see that the smallest 2" trap available is 4-9/16" from center line of bottom of U bend to centerline of outlet, or 7" from bottom of U bend to top of outlet hub (where I guessed the hub adds 1/16" to the radius).

I'm unclear on this plumbing wall--is it a wall above, meaning your shower must have its drain at the edge (e.g. a linear drain), or a wall that happens to be below, meaning you can let the trap penetrate that wall's top plate?

As Jim says, having other than a straight vertical tailpiece between drain and trap has some negatives, so there's probably a better alternative. Which is why I'm asking about the above.

If the wall is below, and you are using a centered shower drain, seems to me it would be worth moving the drain off center (with a custom pan if required) to allow a vertical tailpiece.

If all else fails, I'm not aware of a prohibition on adding the horizontal offset to the fixture tailpiece before the trap. You'd want a LT90 to go from vertical to horizontal, and then a medium 90 (or LT90) to go from horizontal to vertical for the trap.

Cheers, Wayne

Jim and Wayne,
Thanks for the input. To clarify this is a custom pan, with a trench drain running parallel to a plumbing wall which is part of the new bathroom and runs down through the first floor and basement and is all open studs at present. There is a finished bathroom below the new one. I am redoing the supply and DWV in this part of the house.

If I elbow the shower drain through 1 joist, I can cut the bottom/top plate in the plumbing wall to accommodate the trap and sanitary tee. It will only make the arm long enough to reach from the center of the trench drain at this end of the shower to the wall, probably the distance of the 2 elbows.

I am going to relook at the job and see if I can cheat by cutting the subfloor in that area to squeeze the trap in under the tile.

SeaDave

 

[wwhitney]

A few more thoughts:

- Maybe a trench drain that has a horizontal or 45 degree outlet, rather than a vertical outlet? Then if it's on the floor tight to the plumbing wall, the outlet could immediately turn vertical into a trap and be under the plumbing wall.

- There's also a style of trench drain where the trench is in the wall, and the lowest row of wall tile above it is on a removable cover to provide access to the trench grate.

- If the portion of the 2x6 plumbing wall abutting the shower is not carrying any other DWV, you could change it to 2x4s to gain 2" of additional depth and so that the trench drain outlet can be over the plumbing wall below.

- And of course a small soffit in the bathroom below would be an easy solution, but presumably is undesirable.

Cheers, Wayne

 

[Jadnashua]

There are some trench drains where the outlet is horizontal versus vertical, and on those, it is usually at one end versus in the middle.

 

[SeaDave]

A few more thoughts:

- Maybe a trench drain that has a horizontal or 45 degree outlet, rather than a vertical outlet? Then if it's on the floor tight to the plumbing wall, the outlet could immediately turn vertical into a trap and be under the plumbing wall.

- There's also a style of trench drain where the trench is in the wall, and the lowest row of wall tile above it is on a removable cover to provide access to the trench grate.

- If the portion of the 2x6 plumbing wall abutting the shower is not carrying any other DWV, you could change it to 2x4s to gain 2" of additional depth and so that the trench drain outlet can be over the plumbing wall below.

- And of course a small soffit in the bathroom below would be an easy solution, but presumably is undesirable.

Cheers, Wayne

Thanks!

 

[Terry]

I would never install a 1.5" or a 2" pipe in a 2x6
I would either run between, or go below and install a soffit to cover the pipe.

 

[SeaDave]

I would never install a 1.5" or a 2" pipe in a 2x6
I would either run between, or go below and install a soffit to cover the pipe.

Thanks Terry.

I have one more trouble spot I am trying to solve. In the downstairs bathroom below this, the toilet drain currently runs from flange to sanitary tee with a side 2” vent, (1’ long) through a 2x8 joist, then diagonals left and down to the main stack, crossing a future family room and window on the way (red circle in the photo). I want to reroute this into the plumbing wall on the other side of the joist that the vent penetrates. then it will run in the fitting wall along the basement wall, underneath the window to the stack.

Ideally I want to use a closet bend to run the drain 2’ between the joists and pass through the joist where a previous hack completely cut out the joist for a tub drain (blue circle in photo (3’total run from blue arrow) to the sanitary tee. We have supported the joist with a new wall in the basement.

If it works I would use a 90 to go through the opening into a sanitary tee and vent at that point, while draining into the line picking up any the drains. Is it ok to make this short run before venting? I prefer to ditch the current sanitary tee vent so the line can run up in the ceiling. If I can’t run it that far to a vent, can I use a low heel 90 or a 90 with a side inlet to run the vent where it is now?

Thanks again!!!

SeaDave

 

[wwhitney]

UPC allows you 6' from the closet bend to the vent takeoff for a WC. You can use a LT 90 to get through the gap in your joist.

To me it would seem worthwhile to sister across that gap with a piece of joist as long as will fit between things penetrating the joist that won't be removed, even if you leave both sides of the joist supported by walls below.

Cheers, Wayne

 

[Terry]

If I'm worried about height on picking up my fixtures, I will lay a wye or a combo on it's side, and use a 90 going up from there. So for a toilet, looking at it from the top, it would drop into a 90 which then points into a wye on it's side.
I think it could be best to not go through the joist, but hole pretty tight to the bottom of them.