How would one plumb two bathrooms from one rough-in?

Question

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?

Answer 1

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.

Answer 2

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.