Wet Rooms: Open Shower and Tub Zones Explained

A wet room takes the curbless shower one step further. Instead of a shower area with its own pan, the whole bathroom floor, or a large zone of it, is waterproofed and sloped to a drain. The shower is just an open part of the room, and often a tub sits in the same wet zone. Done well, it is the easiest bathroom in the house to clean and to move around in. Done poorly, it is a damp room with a wet toilet. This page explains what it takes.

What makes a room a wet room

Three things define it:

• A waterproofed floor beyond the shower. The membrane covers the wet zone and usually the entire floor, turned up the walls at the edges.
• A floor that drains. The wet zone slopes to one or more drains with no curb or step.
• No full enclosure. At most a fixed glass screen to keep spray off the rest of the room.

The most common layout in a primary bath puts the shower and a freestanding tub together behind one glass wall, with the vanity and toilet on the dry side. Getting out of the tub onto a floor that can take water is part of the appeal.

Small wet room or large wet room

Full-room waterproofing

In a standard shower the waterproofing stops at the curb. In a wet room it continues across the floor and up each wall at the edges, so water that reaches any part of the floor stays above the membrane and runs to a drain. Walls in the spray zone are waterproofed to full height. The TCNA, which publishes the tile industry's installation methods, says of bonded membrane showers that the membrane must cover the solid backing under the entire area to be tiled.

Corners, the drain connection, pipe penetrations, the doorway and any niche are the weak points, and each needs its own detail from the membrane maker. The waterproofing explained page compares sheet membranes, liquid-applied membranes and foam board systems; a wet room uses the same systems over a larger area.

Drains and slope

Most wet rooms use a linear drain along the shower wall, because it lets the floor fall in one plane and accepts large tile. A center drain is possible but needs a four-way slope and smaller tile. Some rooms add a second drain near a tub, or slope the whole floor gently toward the shower drain.

The plumbing code sets the slope range for the shower floor and a minimum drain size; those numbers are on the bathroom plumbing code page. Recessing the floor to get the slope is the same structural work as for a curbless shower, explained in curbless showers.

Ventilation matters more

An open shower puts its steam straight into the room, and a wet floor takes time to dry. Washington requires a bathroom exhaust fan; a window alone does not count. The required rate, from WAC 51-51-1505, is on the ventilation code page.

For sizing, the Home Ventilating Institute recommends 1 cfm per square foot of floor for bathrooms up to 100 square feet, with exhaust points over or near the shower or tub, and recommends running the fan for 20 minutes after the bathroom is used. In a wet room, a fan on a humidity sensor or timer, located over the wet zone, does the most good. See bathroom exhaust fans for what to compare.

Electrical in a wet room

The plumbing code treats the floor of a room with a curbless shower as a wet location (2021 Uniform Plumbing Code section 408.5). Washington's electrical rules add their own limits near showers and tubs: fixed electrical equipment with exposed grounded metal parts inside an enclosed shower area or within five feet of the top inside edge of a tub needs GFCI protection (WAC 296-46B-210), and luminaires within an enclosed shower area or within five feet of a tub's waterline must be enclosed unless listed for that use (WAC 296-46B-410).

In practice, plan lighting, receptacles, heated floor controls and any towel warmer around the wet zone at the design stage. The bathroom electrical code page has the details.

Floors and finishes

• Floor tile: choose tile rated for wet floors. ANSI A326.3 is the test method for wet slip resistance (DCOF); for level interior floors expected to be walked on when wet it uses 0.42 or greater as the benchmark. Ask for the tile's DCOF and use category on the spec sheet, and expect smaller tile with more grout joints in the shower area itself.
• Walls: porcelain tile or large panels in the wet zone, with waterproofing behind; paint only where water does not reach.
• Heated floor: a heated floor helps a wet room dry and is pleasant on bare feet. It goes in with the floor build-up.
• Fixtures: wall-hung vanity and toilet make the floor easy to rinse and dry.

Who a wet room suits

A good fit if you want an open shower and tub zone in a primary bath; you need a step-free bathroom for a wheelchair or walker; or you want the fewest edges and seams to clean.

A poor fit if the room is a busy hall bath shared by children (more water, more often, on more of the floor); the floor framing cannot be recessed; or you dislike a room that stays damp after a shower.

What it costs

In JDI Construction's published planning ranges, a full wet-room build is a $6,000-$14,000 add-on to a bathroom remodel, on top of the base range for the room. Floor framing, how much area is waterproofed and the drain layout move it within that range. The base ranges by bathroom type are on the bathroom remodel cost page.

Finished examples of open showers and other layouts are in our bathroom projects. If you are weighing a wet room against a curbless shower, a free in-home consultation and 3D layout is the quickest way to see both in your own room. Start on our Vancouver shower remodeling page.