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Tub drain over joist

byrd48's picture

I'm installing a bathtub in an old house and the drain happens to be right on top of a joist, and the joist runs the length of the tub, so I need to offset the drain if I don't notch the joist.  I would prefer not to notch it if I can get away with it.  I was looking at this flex drain and was wondering if it would allow me to rotate the drain enough to drop through the floor beside the joist, then connect the overflow to it.  Does anyone have experience with these and know whether or not it would work?



It can work, but depends on the degree of offset needed....... (post #207033, reply #1 of 8)


        I have used a pvc flexible trip waste / overflow to offset around a floor joist. There are brass / bronze alloy trip waste assemblies that have an offset feature. Gerber and Central Brass Corp make them - good luck .....................MikeL

i've installed the flex (post #207033, reply #2 of 8)

i've installed the flex drains also.  it's one of those "it might work, it might not work" type of things.  if it doesn't work what we usually do is to cut out the joist and box of the area that needs to be accessible with double headers on both ends to support the joist that was cut out. 

I was kind of afraid of that. (post #207033, reply #3 of 8)

I was kind of afraid of that.  In this particular situation, I really don't want to cut out the joist.  If I put in the drain and overflow independently, is it possible to join them in a wye under the floor before the p-trap?  It still would not solve the problem of having access to the drain assembly from under the floor in the future.

I wouldn't be so reluctant to (post #207033, reply #4 of 8)

I wouldn't be so reluctant to notch the joist. Plumbers do it all the time (and we curse them when they don't reinforce it) but if you're in charge of the project then you can scab on plenty of 2x6 or 2X8 plates.

Considering that this is under a bathtub the floor deflection will not likely suffer at all, especially if you provide lots of backup lumber.

reinforcing plate (post #207033, reply #5 of 8)

Check this  Then look at their reinforcement plates.  They sell a metal plate that you screw on the side of the notch joist.  They have detailed instructions should read them before you consider using it.

Slick!  Thanks for that. (post #207033, reply #7 of 8)

Slick!  Thanks for that.  Added to building bookmarks.

YAY!  I love WYSISYG editing!  And Spellcheck!


If you use a pvc waste and (post #207033, reply #6 of 8)

If you use a pvc waste and overflow (trade term for the tub drain assembly), it will be made of 1-1/2" pvc. This will let you make an offset (using 2 45's)  in the overflow, or vertical, portion of the assembly to get to the side of the joist. As for the tub drain, or horizontal part, you can then angle it to line up with the tee that connects the vertical and horizontal parts.

This way, if any notching is needed for the horizontal part, it will be very shallow, and should not require any reinforcement at all.

you simply need this and you (post #207033, reply #8 of 8)

you simply need this and you can route around a joist:  

If I could edit my location it would say I'm now in Reno :-)