Curbless shower
Also called: zero-threshold shower, barrier-free shower, roll-in shower, walk-in shower no curb, flush shower
A shower with no curb or threshold — its floor is flush with the bathroom floor and slopes to a linear or center drain. Built by recessing the floor, using a sloped tray, or raising the rest of the room. The accessible standard; $9,000–$18,000 built, and not a DIY project.
A standard shower keeps water in with a curb 2–4 inches high. A curbless shower keeps it in with slope and drain placement alone: the floor inside the shower drops 1/4 inch per foot (1/8 on some linear-drain designs) from the room level down to a drain along the back wall or in the center, and the waterproofing membrane runs out of the shower and across part of the bathroom floor so splash and overflow can’t reach the subfloor.
The problem is the drop. A 5 ft shower at 1/4 in per foot needs its far edge 1.25 in below the room floor, and there’s nowhere for that to go in a standard floor. The three fixes: recess the floor by cutting the subfloor and sistering or notching joists (structural work, often with an engineer’s sign-off), use a pre-sloped tray designed to sit in a recess or on a thinned subfloor, or raise the bathroom floor outside the shower by an inch or more, which means a step at the door. A linear drain at the back wall lets the whole floor slope one way, which is why large-format tile works in curbless designs and why the drain choice comes first.
It’s the spec for wheelchair access (a 36 in clear opening, a fold-down seat, grab-bar blocking) and increasingly a design choice. It’s also the shower most likely to leak when built by someone who hasn’t built one — the slope, the membrane extension and the drain connection each have to be right — and the reason the walk-in shower comparison marks it hire-only.