A bathroom is a question of where the water can go, and in the Burbage core the front of the building is effectively off limits, which narrows it.
With the house standing on the footpath, a soil pipe on the front elevation is both a conservation area problem and a practical one, since it would sit within touching distance of the public pavement. Everything routes to the rear. On a small cottage that can genuinely limit where a bathroom can go, and it is worth working out before a suite is chosen rather than after.
Floors are the second constraint. Older upstairs joists were sized for a bedroom, not for a filled bath on a tiled floor, and in a small cottage the spans are short but the timbers are often light. Where a waste run means notching or drilling them there are permitted zones, and we will move a fitting a foot rather than cut a joist where it must not be cut.
Ventilation gets treated as an afterthought and causes years of trouble. An extractor discharging into a roof void puts moisture straight back into the building and in an older Burbage roof it finds the timber.
Tanking is not optional on a walk in shower. Our bathroom installations page sets out what a full refit involves.