Curbless Showers: How They Are Built and When They Work

A curbless shower looks simple: the bathroom floor runs straight into the shower with nothing to step over. Getting there is a structural job, because water still has to run downhill to a drain and stay inside the shower. Whether it is practical in your home depends mostly on what is under the floor. This page explains how curbless showers are built, how they keep water in and which homes suit them. For the full set of shower layouts, see shower types compared.

Why the floor has to drop

A standard shower sits on a base or mortar bed that rises above the bathroom floor, and the curb contains the water. Remove the curb and that sloped bed has nowhere to go but down. The shower floor at the entry must be level with the bathroom floor, and it must fall from there to the drain.

The model 2021 Uniform Plumbing Code, section 408.5, requires a finished shower floor to slope uniformly toward the drain at no less than 1/8 inch and no more than 1/2 inch per foot. Add the thickness of the waterproofing, mortar or foam tray, setting material and tile, and you need a recess of a few inches in the shower area. There are three ways to get it.

Lowering a wood-framed floor

Over wood joists, the usual approach is to lower the subfloor in the shower area. Depending on the framing, the joists in that area are cut down and reinforced, new framing is added between them at a lower height, or the joists are replaced with deeper members so the top can be lowered. Any change to joist depth is a structural change and has to be designed for the span and load.

Raising the rest of the floor

When the joists cannot be lowered, the bathroom floor outside the shower can be built up to the height of the shower's sloped bed. That keeps the structure untouched but creates a step at the bathroom door, which defeats part of the purpose and has to be handled with a threshold transition. It works best where the bathroom floor is already being rebuilt.

Cutting a concrete slab

On a slab, the concrete in the shower area is cut out, the drain is set lower, and a new recessed floor is poured. It is noisy, dusty work, and it is also the moment to deal with the drain line beneath the slab. The TCNA Handbook has a method specifically for this, B421C, a barrier-free shower on a concrete substrate with a mortar bed floor and a bonded waterproof membrane.

Linear drain or center drain

Linear drains suit curbless showers well because the floor falls in one plane, so the entry edge can sit dead level with the bathroom floor while the rest drops away. A linear drain across the entry catches water before it leaves the shower, though it means you step over the grate. A drain along the back wall keeps the grate out of the way.

Washington's plumbing code requires a shower drain outlet of at least 2 inches (WAC 51-56-0400, UPC 408.4). A narrow exception for some tub-to-shower conversions is explained on the bathroom plumbing code page.

Keeping the water in

With no curb, containment comes from design choices that work together:

• Slope away from the entry. The entry is the high edge of the shower.
• Length. The farther the showerhead is from the opening, the less spray reaches it.
• Head and valve placement. Point the head along the shower, not at the opening. The code already expects controls on a sidewall so you can adjust them before stepping into the spray.
• Glass. A fixed panel along the open side, with a gap at one end to walk through, stops most splash. See shower glass and doors.
• Waterproofing past the shower. Because water can cross the entry, the membrane should continue onto the bathroom floor, and many builders cover the whole floor. Our waterproofing explained page covers the systems.

The wet-location rule

The 2021 Uniform Plumbing Code, section 408.5, says that where a shower has no threshold, the floor space within the same room is considered a wet location and must comply with the building, residential and electrical codes. In practice that affects the flooring, the waterproofing outside the shower and the electrical fixtures and devices near it. How Vancouver inspectors apply it to a particular room is worth confirming at plan review; the bathroom electrical code page covers the Washington rules for lights and equipment near showers.

The bathroom floor should also be slip resistant when wet, and it should be one continuous surface with the shower floor or a deliberate transition. The flooring choice is part of the same decision.

Which homes suit a curbless shower

• Easier: a bathroom over a crawl space or unfinished space with sawn lumber joists and access from below; a slab home where the bathroom floor is coming up anyway; a full remodel where the whole floor is being rebuilt.
• Harder: a second-floor bathroom over a finished ceiling; I-joists or trusses under the bathroom; a joist direction that runs the wrong way for the drain; a small remodel that was meant to leave the floor alone.

Curbless for accessibility

For a private home there is no code requirement to build a curbless shower. If accessibility is the goal, designers often use the 2010 ADA Standards as a reference: they allow a threshold no higher than 1/2 inch at a roll-in shower (section 608.7). A curbless shower with grab bar blocking in the walls and a handheld shower on a slide bar is the core of an aging-in-place bathroom.

What it costs

In JDI Construction's published planning ranges, a walk-in or curbless shower is a $4,000-$10,000 add-on to a bathroom remodel. Where the floor framing or slab work lands in that range depends on what is under your floor; hidden damage found when the floor is opened is handled by written change order. Whole-bathroom ranges are on the bathroom remodel cost page.

Questions to ask before you commit

• What is under the bathroom floor, and has anyone looked from below?
• Will the joists be lowered, the floor raised, or the slab cut? Who designs the structural detail?
• Where will the drain go, and which drain type fits the tile you want?
• How far will the waterproofing extend beyond the shower?
• How long is the shower, and where does the spray point?

Our article on curbless shower design shows more examples. JDI Construction checks the floor structure at the free in-home consultation, before a curbless design is drawn, so the plan reflects what your house allows. Start on our Vancouver shower remodeling page.