Short definition
A shower curb is the raised lip at the entrance of a stand-up shower stall — keeps water inside the shower. Standard residential curb height is 3 to 6 inches; finished with tile, stone, or solid-surface material. ADA-accessible designs cap the curb at 1/2 inch or less (or eliminate it entirely as a curbless shower).
What it is
The curb is built up from framing — typically two or three stacked 2x4s on edge — wrapped in waterproofing membrane and topped with a finish material. The interior face slopes back into the shower; the top is slightly crowned so water sheds inside; the exterior face stays vertical against the bathroom floor.
Code dimensions:
- Shower compartment. Minimum 1024 square inches with at least 30 inches in any dimension (IRC R307.2).
- Curb height. Typically 3 to 6 inches on standard residential. Varies with code adoption and shower-stall size.
- ADA accessible. 1/2 inch maximum (or curbless / roll-in design).
WA adopts these through WAC 51-50 / 51-56.
Why it matters to a homeowner
For a standard shower install, the curb is mostly a question of “is it correctly waterproofed?” The two most common shower leaks in residential remodels happen at the curb corners — where the curb meets the pan and where the curb meets the side walls. Pre-formed CPE or PVC corner pieces (called “dam corners”) seal those joints; skipping them is the start of a slow framing-rot story.
For an aging-in-place remodel, the curb decision flips: most accessibility-focused remodels eliminate the curb entirely (curbless shower) or reduce it to the ADA-minimum 1/2 inch. The 3 to 6-inch curb that protects against splashes also blocks walkers, wheelchairs, and shower benches.
Common failure modes
- Curb leaks at corners. Improper waterproofing where the curb meets the pan or side walls. Use CPE dam corners.
- Tile cracks on curb top from impact. Heavy traffic over a tiled curb top eventually cracks the surface; re-tile.
- Curb wood framing absorbs water. If the membrane is punctured or never installed correctly, the framing rots over years; major remediation.
Common variants
- Curbed shower (this entry) vs. curbless shower. The defining decision in any modern shower remodel.
- Tiled curb (built up with mortar plus waterproofing plus tile) vs. solid-surface threshold (single piece of stone or quartz).
- ADA low-curb (1/2 inch) vs. standard residential curb (3 to 6 inches).