Falls and the soil connection
Waste pipes run on a fall, and a bathroom has to find that fall within the floor depth available. A bath and a shower tray both sit low, so getting a continuous fall from them to the stack is often the single constraint that decides where the shower can go at all. Where the stack is on the other side of the room, the fall needed over that distance may mean a step up into the shower or a different layout.
A WC needs a short, direct run to the soil stack. Moving a toilet more than a couple of metres means either a macerator, which brings its own rules and noise, or opening the floor.







