Bathroom Plumbing

Showers and tub-shower combinations need a pressure-balancing or thermostatic mixing valve. That is the device that stops the shower from going scalding when a toilet flushes somewhere else in the house, and it is a code requirement rather than an upgrade. Moen Posi-Temp and the Delta MultiChoice universal rough are common choices because the rough valve is standardized and the trim can be changed years later without opening the wall.

The detail that gets missed is depth. Every valve body has a range showing how far it can sit behind the finished surface, and that finished surface is backer board plus waterproofing membrane plus thinset plus tile. Guess the assembly thickness wrong and the trim plate either floats off the wall or the stem is too short to reach it. We confirm the build-up with whoever is tiling before the valve is strapped in place.

Older houses bring a second issue. A modern pressure-balance valve fed by 1/2 inch galvanized that has scaled down internally will behave badly no matter how well it is installed, because it is being starved. Replacing the branch piping while the wall is open is the fix.

A tub and a walk-in shower are different jobs below the finished floor. A tub uses a waste and overflow assembly that has to stay reachable, so somebody has to decide at rough-in whether that access comes from an adjacent closet, a removable panel, or the ceiling below. A walk-in shower uses a bonded drain body that ties into the waterproofing, either a centre drain or a linear drain along one edge, and the membrane clamps or bonds to it. Schluter and Hydro Ban each have their own drain, and they are not interchangeable.

That creates a handoff. We set the drain and the rough-in, the waterproofing goes on, and a flood test proves the pan before a single tile is set. Where the tile setter is doing the membrane we agree on the drain in advance so the parts match. Skipping the flood test to save half a day is how a shower leak becomes a ceiling repair.

Curbless showers deserve a separate warning. A flush entry usually means dropping or furring the floor structure, which is a framing decision as much as a plumbing one, and on a second floor over a finished ceiling it is not always possible.

Floor-mount toilets are straightforward: a flange set level with the finished floor, a proper seal, and bolts that are not overtightened into a cracked base. Wall-hung toilets need a steel carrier and an in-wall tank, so the wall has to be deep enough to take it, usually 2x6 or furred out. In a condo or a small powder room the floor space you gain is real, and so is the cost of building the wall to suit.

Moving a vanity is where venting comes up. The trap arm has a maximum developed length for its size, and it can only fall so much over that run before it siphons its own trap. Push a sink far enough from the stack and it needs a new vent, which means opening a wall up to the vent connection.

An air admittance valve is sometimes accepted as an alternative. We use them where they suit the situation, but they are a mechanical device with a moving part sitting inside a wall, they have to stay accessible, and an inspector may not accept one where a conventional vent could reasonably be run. If we recommend one, we will tell you why the alternative was worse.