Adding bathroom

We want to put a full or 3/4 bathroom in my daughter's bedroom, which is over the garage. One contractor suggested locating the new bathroom so that it would share a wall with the downstairs half bath and use the same piping. However, this placement would allow only a very small, narrow half bath. We would like to locate it at the other end of the room, which is upstairs and across a stairway from the laundry room. We could run piping, etc., through a crawl space that is over the stairway and laundry room. My questions: Is this feasible? Would we run into any contamination, odor, etc. of the washing machine? Would we need to replumb the washer lines? Any other thoughts? Thanks for any help--I am a total novice, though my husband has some limited plumbing experience.

Well, almost anything is possible...if you're will/able to pay for it. You have some potential problems in doing what you want to do. The most obvious of these is the drain. A drain must slope 1/4" per foot or 1" per 4 feet, and I doubt if there is space to run the drain under the floor. If the drain would be over the garage, perhaps you could have it exposed under the ceiling, but a toilet drain must be at least a 3" pipe and can't just tied into a drain of smaller diameter. Me thinks you'd better contact a plumbing contractor anyway, because this is not a job for someone with no experience or knowledge, there are too just many pitfalls.

bathroom

Usually it is easier to place the new one somewhere other than behind an existing bath. Trying to use the existing piping usually requires that the whole system has be removed and revised. It usually easier to run a pipe to the new location and start from scratch with the piping for just that one bath.

Thanks for the input. We do have room to run the drain pipe across the top of the garage, since the ceiling there is about 16 feet high. We would definitely use a contractor, but weren't sure if this idea was even feasible. It sounds like it might be better than tying in to the downstairs bath, both from a plumbing perspective as well as from size concerns. Would a washer have at least a 3" pipe? What other problems can you foresee?

A washer only needs a 2" drain, but larger is good.