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I am in the planning stage to finish my basement. There is a rough-in with drain for toilet and shower. My plan is to add at least two bedrooms with one being a master. Thankfully the rough-in is located in the middle-ish of a long wall.

Is it possible to add a half bath immediately adjacent to the master bath in such a way that the toilets share a 4" drain without tearing into the cement?

If necessary I don't mind raising the floor to create a 1/4"-per-foot downward slope. Assume that the drain and main stack are equidistant between the two toilets on either side of a common wall.

Are there any problems with this in terms of flow or venting? How would one go about it?

Alaska Man
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Tag
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  • If you can raise the floor enough sure you could but that’s a big step do you have enough height? Remember you would have to raise enough for flooring above the pipe you could run joist along the pipe but in reality you are talking about a 6” step, I would want to cut the slab unless you have 8-1/2’ or 9’ ceilings now. – Ed Beal Jan 12 '21 at 15:21
  • @EdBeal It's a 9' ceiling. – Tag Jan 12 '21 at 15:25
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    Putting the toilet on a platform so you've got room for plumbing/slope before it will really make it a "throne"! – FreeMan Jan 12 '21 at 17:06
  • I thought the OP wanted everything elevated so it could use the 4” as the main line not just the throne but have seen just that done also. – Ed Beal Jan 12 '21 at 18:15

2 Answers2

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You are "f'ing" crazy if you think that raising part of your floor is easier than doing some very very minor concrete work. There are all these gotchas for raising a floor and then finishing it so it doesn't look ghetto.

Now for doing it right there is breaking concrete, creating a bed for pipe, laying pipe, backfilling, and then adding in quickmix concrete. It is 8 hours of work. You will spend days trying to figure out how to put a toilet on an elevated box that looks OK.

Just do it right. The elevated floors should be a last case emergency thing. I have finished hmmmmm maybe 50+ basements never have I raised the floor to tie into the stack.

Also from a DIYer perspective, when you are breaking the concrete and filling... there is nothing anyone can see. You can mess something up or have a half assed finish and no one sees it. You raise floors and every carpentry thing sticks out like a sore thumb, every edge, every finish. You may be scared to break the sledgehammer out on the floor but in reality you are creating 5-10 times the work for yourself AND IT WILL LOOK WORSE EVEN IF YOU FINISH IT GOOD.

Note: The hardest part of breaking up a basement floor is carrying buckets of concrete out (assume 20) and disposing them. Everything else is really easy. I did want to mention this because it is a workout.

DMoore
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  • I agree and did mention the step you and I both would know it was diy in most cases unless the one case the floor was poured after and almost in contact with the slab at that point. I did mention cutting the slab in the comments. – Ed Beal Jan 12 '21 at 18:11
  • Hmmmmm. What about using a rear discharge toilet? They accept drain pipe several inches in the air. Then the floor wouldn't have to be raised. – Tag Jan 12 '21 at 18:23
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    Why Tag? Why? I am telling you if you do something wonky like rear discharge or raised floor, after finishing the basement and doing all of that hard work you are going to say, man why didn't I just break up a few feet of concrete. If it weren't easy I wouldn't suggest it. I would trust a home owner doing this vs installing wood floors. I get that its "diffirent" but there are youtube videos that walk you through it. – DMoore Jan 12 '21 at 18:55
  • This is a greenfield project. Cutting the slab scares me. Unlike the rest of the work I could break something that I don't know how to fix. – Tag Jan 12 '21 at 19:11
  • It's funny. I finally understand why some people are so afraid of computers. Thank you for that. =) – Tag Jan 12 '21 at 19:14
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    As long as you don't swing sledgehammer after concrete is broken up you can't "break" anything. Trust me you won't be breaking off 2 feet of concrete at a time or super chunks. The only thing you can mess up is take the concrete out near stack and still swing away. If you are using just sledge hammer vs renting a jack hammer - please do not do it in one day or expect blisters. On sites I have time I sit a sledgehammer down and spray paint the knock out zone and let my guys take turns to get out aggression. Much more fun that way. – DMoore Jan 12 '21 at 19:33
  • Also there are a lot of guys that you can find on craigslist that have probably done this 100+ times. I have two brothers that come out and do this for me if I need something that day and they are two 50 year old guys that argue with each other like kids and argue about whose turn it is to take the bucket of broken concrete up as they go along. They charge me $150 for an average knockout then $100 for a pour (you can't do them same day as city needs to inspect after you connect). But yes very doable for a homeowner. – DMoore Jan 12 '21 at 19:40
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    Also understand breaking up your floor near stack has zero to do with moisture getting into your basement or your foundation collapsing. The floor is just a thermal break from the soil. – DMoore Jan 12 '21 at 19:56
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    Tag, take the good advice here. Don't let your intimidation lead you to a horrible compromise _in a new home_. I use rented diamond blade saws for this kind of work. If you can handle a chainsaw--or know someone who can--you can do this simple slab surgery. – isherwood Jan 12 '21 at 21:14
  • *How would one plumb two bathrooms from one rough-in?* ... by changing the rough in to accommodate it, duh lol +1. If we're not passed rough in it's not even a question. After a few thousand dollars of tile is in the way is a different story. – Mazura Jan 13 '21 at 01:05
  • @Mazura - that only works in Australia. – DMoore Jan 13 '21 at 04:59
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With a 9’ ceiling you can do what you want without cutting the slab. The only negative is there will be a step into the bathroom (not a horrible thing I have had to do this for a 1/2 bath because the drain itself was directly below the slab on 1 house. I would be aware if there are roughed in showers, those traps will be below the concrete normally and you don’t want 2 traps that would not drain well. So there is a possibility of an issue there. If everything is replumbed to the 4” I don’t see any major issues with a 9’ ceiling.

Ed Beal
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  • Unfortunately cutting the slab is outside of my comfort zone and pulling in a contractor would likely blow my budget. Only the master will have a shower so the traps shouldn't be an issue. Thank you for the warnings! – Tag Jan 12 '21 at 16:00
  • I have a feeling you are answering to raise floor height to boost the amount of questions on this site. He will surely have 20 more questions after he decides to do this :) – DMoore Jan 12 '21 at 17:51
  • Well not intentionally, I did mention if a shower rough in the 2nd trap issue , have seen that before. – Ed Beal Jan 12 '21 at 18:07
  • @EdBeal - just messing with you but we have to get volume up somehow! – DMoore Jan 12 '21 at 18:55
  • They'd all be dupes but if there's pictures we can't seem help ourselves but to answer them ;) – Mazura Jan 13 '21 at 01:04