Moving toilet waste line through floor joists

Any advice or experience on moving a 4" PVC toilet waste line through two, 2x12 floor joists? Is this stupid or is there some bracing that would help keep the structural integrity of the floor joists in tact? This is a second story bathroom.

Supply lines are small, so they can usually run laterally through holes or notches in floor joists, but this isn't possible for 1 1/2" to 4" or larger drains. For standard dimensional joists, code forbids any joist notching in the middle 1/3 of span and allows you to remove only 1/6 of their depth in the other 2/3. You may not drill a hole any larger than 2 1/2" in a joist or any closer than 2 1/2" from the top or bottom. Thus, unless your waste lines can run parallel to the joists, you'll have to raise the floor, lower the ceiling or create a soffit below. Maybe someone else will chime in with ideas.

Jason

The only way to do it is to replace the structure with an engineered reinforcement.

First, is it necessary to use 4" pipe? There is a big difference if the run from the toilet to the main drain can be 3" pipe.

You need access to the joist from above or below.

If you have to notch the bottom of the joist, then a full 2x8 on BOTH sides of the remaining section will give you the equivalent strength. It should run at least five feet either side of the notch and be supported at the end if that puts the end over the bearing wall. Use at least ten 3" nails, uniformly distributed in the 2x8, on each side of the cut. That's 40 nails per 2x12 that you cut. The notch should be rounded, not a square corner cut. Do the best you can with a saber saw.

If the hole is in the middle of the 2x12, then you need 2x6s. Put one on each side above and below the notch. Put rounded notches in the 2x6s to accommodate the pipe. Notch the bottom of the 2x12, put the top 2x6s in place, install the pipe, and put the bottom 2x6s in place. This is a different loading (tension in the 2x6s instead of bending in the 2x8s above), so you actually need more nails (put 20 in each end of each 2x6, staggered, spaced) to develop the full tensile strength of the 2x6.

Rent a framing nailer for all this nailing.

Apply a liberal layer of yellow carpenters glue to each interface for both joints (2x6s or 2x8s).

When you are done, the structure will be at least as strong as the original.

Be sure to support the 2x12s while they are cut so your floor doesn't sag.

Good info, Bob. I didn't think that many nails would be needed. I will have to add some to my bathroom repairs when the ceiling is opened up below for kitchen remodel. I used 4 carriage bolts on each side.

Bob NH said:

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Apply a liberal layer of yellow carpenters glue to each interface for both joints (2x6s or 2x8s).
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Why not use some liquid nails or something else with better non-water-soluable holding power?

How about some diagonal bracing in addition to the modifications above?

Jason

Liquid nails would probably work but I don't know its shear strength. The yellow glue will usually fail the wood first in a flat joint.

The large number of nails is required to develop the tensile load in the 2x6s to replace the strength lost in the 2x12. There will be about 4000 pounds of tensile load in the bottom 3.5 inches of that 2x12 at the design load. A 10d nail has an allowable load of about 200#, so 20 would be required to develop 4000# tension. I doubled the 2x6s because it is difficult to get a good joint in repairs due to splits and difficult nailing.

The glue has two functions. There is less deflection in a glue joint, because there has to be a small deflection before the nails develop the load. And the glue will prevent squeaks.

The 2x8s are acting like a beam; not in tension. The strength of a rectangular beam is proportional to the width times the square of the depth. The two 2x8s plus the remaining 2x12 section will have about 25% more strength than the uncut 2x12, but they will probably have to be notched a bit also.

In the case of the 2x8s it is only necessary to carry the floor load into the beam; about 60 pounds per lineal foot. Again, more nails to take care of the difficulties of repairs.

Pipe size and location.

I can reduce the waste piple size from 4" to 3". I checked again and I actually only have to pass through 2 joists to move the toilet. In doing so I would need to drill two 3" holes in, roughly, the middle of the joists. What do you think about putting in some sort of metal bracing in or around the 3" holes?

Thanks

Titebond III is waterproof, and it will spread much more easily and completely than trying to use liquid nails. Liquid nails also tends to be a little rubbery, putting more load on the nails.

The holes will have to be about 3 5/8" because a 3" PVC is 3.5 OD.

Is the mid point vertical or in the span?

It takes a lot of nails to hold metal in place because it is usually thin. Take a look at the plates used in truss fabrication.

It is tough to put 3" pipe through multiple holes. You will probably need a bunch of short pieces and couplings.

If you end up with 3 5/8 holes at the vertical midpoint of the 2x12s, then I would reinforce them with 6 ft lengths of 2x4, one above on one side and one below on the other side, attached with glue and fifteen 3" nails on each end. It will be easier to put the pipe through if you do the reinforcement after the plumbing.