Why the Same Bathroom Costs Different Amounts

One: the decade the house was built

Same request, different job

Ask for the toilet to move three feet. In a house over a crawl space a plumber goes underneath and reruns pipe. In a slab house the floor gets cut with a saw, the concrete broken out, the drain rerun in a trench and the slab patched.

Identical request, several times the cost, and the difference has nothing to do with the contractor or the city's labour rates.

Plumbing materials changed over the twentieth century, and the material inside your walls sets a floor under your project. Galvanized steel supply pipe was standard until roughly the 1950s. It corrodes from the inside, so a pipe that looks sound can have half its bore closed with scale. Once a wall is open, most contractors will not tile back over it - and they are right not to.

Cast iron drain stacks are a different question. They often remain perfectly serviceable, but cutting into one to move a fixture is a bigger job than cutting PVC, and it needs someone who knows how to support the stack while doing it. This is the main reason a layout change costs more in an older American house than the identical change in a newer one.

Two: what the house sits on

In a house over a crawl space or basement, a plumber reaches the drains from underneath. In a slab-on-grade house the drains are cast inside the concrete, so moving one means marking the floor, cutting with a saw, breaking out the concrete, re-running the pipe and patching the slab - then redoing the floor above it.

The same slab has an upside people rarely hear about. A curbless, zero-threshold shower needs the shower floor lower than the bathroom floor. Over wooden joists that often means structural work or raising the whole floor. On a slab you can simply recess the concrete, which is why zero-threshold showers are common and affordable in slab regions and comparatively rare elsewhere.

Three: the water and the weather

• Hard water carries dissolved calcium and magnesium. On glass those minerals settle into microscopic pores and eventually bond with the silica - at which point the surface itself has changed and no cleaner reverses it. Factory-coated glass or a whole-house softener are the two things that actually work.
• Cold climates make an exterior-wall supply line a recurring hazard, because wall insulation sits between the pipe and the outside only in theory - in practice the pipe ends up on the cold side of most of it.
• Humid climates put the exhaust fan at the centre of the project. A fan ducted into an attic rather than through the roof is a mold generator, and it is a surprisingly common find.