View Full Version : Swapping tub and toilet--how much work?

Andy Ring
11-26-2004, 07:59 AM
Hi, I'm in the early planning stages of a bathroom remodel. My house was built in the 1880's is 4 stories tall and has elaborate original plaster detailing, etc. I would like to remodel a bathroom on the third floor (which was remodeled about 20 years ago, so has “modern” plumbing). I'm hoping to accomplish the remodel with minimal demo outside the bathroom itself. The bathroom is 11 x 6 with a tub, pedestal sink and toilet all along one long wall. The waste and vent stacks (which go up to another bathroom on the 4th floor) are at the head of the tub along one of the short walls. My optimal new layout would involve swapping the position of the tub and toilet (putting toilet closest to the stack and tub farthest away, about 10 feet). I plan on replacing all floor tile, but would like to leave as much of the sub floor in place as possible. The waste plumbing is black pipe/no hub variety (not sure of sizes). In general, should I be able to just swap a closet flange for the current tub trap and visa-versa leaving the venting pretty much as is? Or, will I need to re-do all the waste plumbing/venting and demo the entire subfloor and wall? I realize it probably depends on how the current stuff is plumbed, but let’s assume it is up to code. I’m trying to finalize my bathroom layout and the amount of plumbing involved in the swap of fixtures will help me make up mind.


11-26-2004, 10:20 AM
From your description, and assuming the piping was put in properly, your project could range from somewhat difficult to impossible. Where it fits on the scale between those two extremes depends on exactly how the pipes are arranged in the floor. Just know, that you cannot use the tub pipes for the toilet by placing a flange on them.

11-26-2004, 12:11 PM
You cannot just swap. You will probably have to take out most of the sub-floor and you may still end up taking out some of the ceiling below. Usually the drain pipes are at the bottom of the joists.

Andy Ring
11-26-2004, 12:25 PM
Thanks for the response. To follow up, if I'm not being too ignorant, what are the requirements for a toilet as opposed to a tub? I've moved toilet's in previous remodels and I helped build a new house, so I have some idea of how a tub and toilet are typically plumbed, but I don't know the specifics about diameter of pipes, different venting requirements, etc. I assume that pitch of the pipe in both is 1/4"/foot? Any basics would help me out--at the moment, I can only guess what my plumbing looks like since its all under the floor.

11-26-2004, 05:45 PM
The MINIMUM requirements would be 3" for the toilet, and 1 1/2" for the tub, although in many cases the tub would be 2" and in some areas the toilet has to be 4". It just depends on the code you are using.

Andy Ring
11-27-2004, 06:47 AM
I guess I will have to ponder my options. I may get back in touch once I've ripped up the floor and can see what's there. Thanks for the advice--wouldn't have liked to commit to a swap and then found out it was a much larger proposition than I had thought. Still may do the swap, but will budget accordingly.

11-27-2004, 07:56 AM
Others have pretty much laid this out for you: it's a big job. I wish I could draw a picture, but let me try with words:

The drain pipe coming from the bottom of the tub is 1½". It leads back to T, then drops into a trap which is probably 2". The 2" line then leads probably towards the main and ties in. The drain under the toilet is minimum 3" and may be 4".

Notice the heavy use of "may" and "probably" because there are seldom any 2 bathrooms where the piping is exactly the same. The installing plumber knows what to do to make it work properly and to code. He has to tailor his installation around what the framers, HVAC people, etc. have left for him to deal with.

We don't automatically discourage people from do-it-yourself projects, but because of the need to change almost all the piping under the floor, we want you to know this is a big project. It could be done; but you may want to consider design options which don't involve moving the toilet.

Andy Ring
11-27-2004, 09:38 AM
Ok, once again thanks...One more (final?) question. Suppose that right now the toilet has 4" pipe and the tub 2". I understand that I can't just do a swap because the new toilet can't work with the 2" pipe. But, would it be ok to assume that I would be able to plumb the new tub into the existing 4" toilet pipe with the correct adaptors. In other words, is using existing 4" toilet plumbing ok for a tub that may only require 2" or 3" pipe? (Assuming you use standard 2" tub trap and then adapt up to 4"). I realize there may be vertical height issues because of the trap, but lets leave those aside right now because I may put the tub up on a platform anyway. Since the new tub is the farthest away from the stack, being able to use the presumably 4" exisitng drain pipe would save me a lot of demo. The new toilet position is right next to the stack, so ripping out the 2" pipe and replacing with 4" might not be super difficult.

Finally, I really appreciate the advice, but don't be shy to let me know if I'm over staying my welcome, so to speak. :o

11-27-2004, 09:57 AM
I would also not make the assumption that the plumbing put in 20 years ago is correct.
You need a plumber to even begin to assess what you can and cannot do--someone who knows what they are doing needs to actually look at this. It is most likely a big project.
The toilet line will have had no p-trap and the trap arm length maximums are greater. So, the toilet may be too far away from the vent to simply bush the line down, and run a new trap arm and p-trap for a tub.
The Pipewench

11-27-2004, 12:19 PM
Using the existing toilet pipe for the tub might be the worst thing you could do. It is very difficult to add a new toilet connection unless you remove the old one, or reuse the existing one, due to vertical space requirements. Once you run the existing toilet opening to the new location, then you will have to figure out how to get the tub opening to the other side of it.