I'm planning on calling a plumber to give me an estimate on my bathroom addition. There is no basement, it is on the first floor on a concrete slab.

I already have a bathroom on the 2-nd floor right above. The cast iron vent pipe is going down through the existing bathroom and I'd like to connect the new toilet, sink to it. I'm also hoping for a shower too but if the breaking concrete will be required I might opt out. enter image description here enter image description here

Is breaking the concrete inevitable? I was hoping maybe the horizontal toilet could still be able to be attached at the bottom. Not sure about the shower as the piping will require a slope.

  • 2
    You could go with a macerating toliet
    – StrongBad
    Nov 27, 2017 at 21:04
  • 6
    Cutting and replacing concrete isn't the traumatic thing folks tend to think it is. When my wife and I were first married I had her help me cut about 20' of channel into our basement floor to replace shrunken iron. The look on her face was priceless when I told her what we were going to do. Now, 20 years later, she thinks nothing of that sort of thing. Just do it right.
    – isherwood
    Nov 27, 2017 at 21:17
  • @isherwood, my eyes almost popped out from removing that floor board. They nailed it with at least 200 nails such a small piece. And now thinking of breaking the concrete? It's gonna cost much more, not sure if worth it.
    – Grasper
    Nov 27, 2017 at 21:43
  • If you do the concrete work yourself it won't cost much at all. Rent a diamond "maniac" saw and do your best to manage dust. Water helps. Your repair won't need to be perfect since you're covering it all with framing anyway.
    – isherwood
    Nov 27, 2017 at 21:45
  • 1
    Foundation and floor slab are 2 different pours, 2 separate units. The cut would be started at the wall where the pipe goes into the floor, opened up enough to see where it goes. Care would need to be used when doing this, cast iron will crack if the chisel gets too close. Even so, a crack may not be that big of a deal, the pipe will need to be cut to add in what is needed to add the toilet.
    – Jack
    Nov 28, 2017 at 0:41

1 Answer 1


I believe you are trying to cram to much in too little of space. The best option is to break the floor, and repair it, it will save you the "step up" you are creating with the 2X4 sleepers on the slab.

You may be able to find a plumber or perhaps DIY the cutting of the stack and tying in a line to the toilet that flushes through the wall. They are out there but it looks like your soil stack is too tight in the corner. You need to find a way to get the soil pipe out of the wall at the 15" mark. Code requires 30" for the area a toilet sets in, 15" is the center line of that space.

Actually the info I just gave will be wrong to a degree. You will need a vent for the new toilet and it will most likely be illegal to tie it into a line that directly serves another toilet with out another branch coming off of the main to serve the new toilet.

  • That pipe is actually a vent pipe and upstairs toilet is connected to it.
    – Grasper
    Nov 27, 2017 at 21:37
  • @grasper then below the upstairs toilet this would just be full of waste if you were correct, but Jack is correct on that point above the toilet is the vent below the toilet is the waste line. With out knowing the length and width there is no way we can state that you are trying to put two much in the space.
    – Ed Beal
    Jul 22, 2018 at 17:09

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