View Full Version : Toilet drain modification

05-02-2007, 01:05 PM
I am in the middle of a bathroom remodel (project from hell). I need to move the toilet down the wall 13". It will mean moving the flange to the other side of a joist. I have a couple of questions.
What is the recommended slope for a drain like this?
I will probably have to notch the joist but should have enough room to sister another piece around it, is this ok?
Any advice on how to cope with cast iron? The flange and 3 elbows are copper running into cast iron)
Any help is appreciated.

05-02-2007, 01:35 PM
.... slope for a drain like this .... notch the joist .... sister another piece around it .... cope with cast iron .... Depends on where in the joist (end near a wall, or center of joist not near a wall) you are thinking about cutting, and on the size of the joist (2x__?).

Slope for drains is 0.25" per foot of run.

I haven't figured out what you meant by "flange and 3 elbows are copper running into cast iron". Did you mean you have 3" diameter copper DWV elbows getting connected to a cast iron drain pipe? I've seen brass flanges on WC elbows made of lead.


05-02-2007, 01:50 PM
He's talking about a brass flange to copper waste line. Even if it's flat to the stack, you won't see any difference.

05-02-2007, 02:07 PM
As plumber1 stated it is probably a brass flange. It is soldered to a 45 elbow thena a tee then another 45 which runs into the cast iron pipe. It is far enough down the wall that I can't see exactly how it is connected to the cast iron.
The notch will be about 9 inches from the supporting wall for the joist. Joist is 2" x 7.5". Originally built in 1946 with 24" centers.
Thanks for the info on the slope.

05-02-2007, 03:18 PM
I wouldn't feel comfortable putting a 3+" hole in a 2x8 although it is done, especially with 24" on center. Could you box it in with a double header on either side? ANy structural engineers out there?

05-02-2007, 04:35 PM
bad news is that it's only a 2x8.
good news may be that the proposed cut is 9" from the supporting wall. May not be good news. Depends. Q: How long are the joists? Distance between supporting walls.

also, can you manage cutting a hole instead of notching the joist? Holes in the center line leave a stronger joist than notches of the same size.

What size hole would that be for your pipe?

ultimately your goal is to make the new sister or support to the joist be just as strong as the joist was before cutting a hole in it.


05-02-2007, 06:37 PM
The notch will be about 9 inches from the supporting wall for the joist. Joist is 2" x 7.5". Originally built in 1946 with 24" centers.

A 4" hole or notch for a 3" pipe going through a 2X8 is only going to leave 3-1/2", or the size of a 2X4, to carry the floor load near a toilet, and I would not want my floor that weak even under a coat closet.

At the very least, triple that joist for at least half its length, then cut the absolute minimum you need to get the plumbing through. And if you want to add even a little more strength, use through-bolts to fasten 1/4" X 3" X 3' steel plates on each side of the tripled joist. A real engineer might say that is a bit overdone, but the toilet will likely stay on its designated floor.

05-03-2007, 05:58 AM
To answer some of the questions...
In order to support the stone floor I will be installing more joists to bring it down to 12" on center.
In order to install the toilet where I need it, I will have to notch (3") the joist but I plan to sister it with 2x8's on both sides.
The span for the joists is only 6.5'

05-03-2007, 06:53 AM
The joists only span 78 inches. That is the best news possible. I might use a 1/8" thick metal strip or angle iron or C channel to strengthen the joists notched.

Are you planning to put electric heat cables in this small Ontario floor?


05-03-2007, 08:56 AM
Floor heater will be installed once all of the plumbing fun is sorted out. I have to figure out how to connect 3" abs to cast iron.

05-03-2007, 09:18 AM

Cast to ABS needs some sort of coupling like this.

05-03-2007, 09:22 AM
The copper pipe that I removed was set inside the cast iron pipe. I didn't even think to check and see if there was a rubber seal ring arond the pipe. If I have to remove the top of the pipe to accomodate a new connection I will be forced to go into the basement and remove a wall for access, then rebuild the entire stack. From what I can see from the top there are no straight pieces of pipe longer than 2" or 3".

05-03-2007, 09:55 AM
Keep in mind that when determining the length of a span for deflection purposes, it is NOT just the room size, it is the length of the joists between supports under them. This could be either a load bearing wall, a beam, or the rim joist. A stone tile floor requires L/720 and two layers of plywood.