Walk-In Shower Installations: Key Steps and Limits

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Walk in shower installations give a bathroom a flush, no-threshold entry in place of a raised curb. Most of the work is in the floor: the shower floor must slope to the drain, the room floor must meet it without a step, and the waterproofing must keep water out of the subfloor. This guide draws on two sources, the U.S. Access Board’s accessibility standards and a City of San Diego installation guide. Before you cut into any wall, floor or fixture, shut off the water, and hire a licensed plumber or contractor for valve, waterproofing and structural work.

Quick answer

A walk in shower, often called a curbless or roll-in shower, has a very low or no threshold at the entry.
The shower floor must slope toward the drain and away from the entry, so water stays inside.
The two sources disagree on thresholds: the San Diego booklet says the codes prohibit them, while the Access Board text sets a half-inch maximum for roll-in compartments.
The San Diego guide calls water control the key design challenge, because the entry has no curb to hold water back.
Federal accessibility text requires a roll-in shower with a seat in certain facilities, and transfer-type showers are not allowed in its place there.
Building codes vary by state, city and building type. Check your local rules before you build.

How we chose these sources

Two sources were chosen because they describe the installation itself and the accessibility rules that shape many shower projects. The San Diego copy is a design and installation booklet with drawings of floor recesses, drains and membranes. The Access Board page is the federal accessibility standard text, which sets out when a roll-in shower and a seat are required. Neither source is a retailer, and no product listing was used. The section order below is arranged by topic. It is not a sequence that either source gives.

What a walk in shower is

The San Diego guide describes a curbless shower as one with a very low or no threshold at all, so a person can walk or roll straight in. It notes that these showers can include a built-in seat, a hand-held shower and grab bars, and that they can still be used to stand and bathe the usual way. The one thing the guide says a curbless shower does not offer is the chance to soak. A home with only this fixture may need a second bathing option, such as a tub.

The guide also says that single-family bathrooms are generally not required to meet accessibility design rules, but multifamily housing with a set number of fully accessible units must follow them if it installs curbless showers. If the goal is easier entry at home, the same design points apply even when no code requires them.

Plan the size first

A shallow shower is harder to keep dry. The guide says the state accessibility code it references and most national standards allow a curbless interior as shallow as 30 inches deep and 60 inches long. It then says 36 inches should be considered the minimum depth for any curbless shower. It describes a 42-inch depth as a significant improvement and 48 inches as better. For a stall that must also let an attendant help, the guide points to a 5-foot by 5-foot shower, which gives room for a person in a shower wheelchair and an aide and lets a wheelchair user turn around.

Narrow stalls with a flexible curtain have a practical problem. Small movements to reach the controls can pull the curtain off the floor, and water then runs onto the bathroom floor. Plan enough floor area for the person to move both inside and outside the stall.

Plan the flush entry

The San Diego guide says the state code and most national accessibility standards prohibit any threshold or curb at a curbless entry. Flush transitions usually mean the shower sits recessed into the bathroom floor, and the shower floor must slope enough that water flows toward the drain and away from the entry. The guide shows three entry profiles:

The Access Board text opened for this guide does not match that statement. It says thresholds in roll-in type shower compartments must be a half inch high at most, and that transfer-type compartments in certain existing facilities may have a threshold up to 2 inches high under an exception for structural reasons. Until your local code is checked, treat the threshold question as open rather than settled.

A preferred profile, which the guide says suits large showers, uses a beveled transition of up to half an inch.
A compromise for narrow showers, where water containment is a major concern, uses a bevel no steeper than 1:2.
A least preferred profile allows a vertical rise of up to a quarter inch. The guide says some people will have difficulty rolling over even that small edge.

There are two ways to make the shower floor lower than the room. The guide calls dropping the floor under the shower the preferred method. Setting the shower directly on the subfloor and building up the room floor usually creates a level change at the bathroom door or in the hallway, which then has to be beveled or ramped. Either way, the guide says the trades must coordinate closely.

Build the floor recess and drain

For a custom-built shower, the guide says the floor structure may need to be reworked to accept a dropped floor. With wood framing, the subfloor is lowered, and the joists are dropped or resized and spaced to carry the load, with extra framing around the recess. With a concrete slab, the slab must be poured with the recess from the start, which changes how the reinforcing and joints work under the shower. The guide says custom units need more careful detailing and good supervision during construction.

A setting bed or mortar bed should cover the whole shower area and be deep enough to slope to the drain. The guide says this usually means recessing the floor about 1-1/2 to 2 inches, and possibly more for large showers. The top of the drain must sit below the room’s subfloor. Its drawings for custom tile floors show a slope of 1/8 inch to 3/16 inch per foot.

The guide recommends a two-stage drain with weep holes. The idea is that water absorbed by the setting bed can seep into the drain instead of staying in the bed.

A prefabricated base is the other common route. The guide says these units generally need less on-site time, and that a one-piece unit removes some of the waterproofing problems of a custom pan. The joint between the room floor and the shower floor still needs attention. Many prefabricated units marketed as accessible still have a low threshold to hold water. The guide says a roll-in unit with even a half-inch threshold belongs only in specific retrofit cases, or where strict code compliance is not required.

The guide also warns that prefabricated bases are shallow and may lack structural strength. Look for a base that is thickened or reinforced around the entry, or one built with a honeycomb-type core. Follow the maker’s bedding compound thickness. The recess must match the base depth of the specific unit. If the recess is too deep, the guide says the unit can be shimmed up to match the floor. If it is too shallow, a watertight seal is hard to achieve.

Waterproof the pan and walls

In both wood-frame and slab construction, the guide says a waterproof membrane should form the bottom of the shower pan. It should run up into the surrounding walls and out onto the floor next to the shower. Its drawings also show the membrane top sitting above the top of the floor drain at the threshold line. Keep the membrane continuous, with no breaks at the wall or the floor edge.

The guide does not name a membrane product, and nothing in it says how long a membrane needs to cure. Follow the membrane maker’s instructions for those details, and have a licensed contractor do the work where a leak would reach the structure.

Control water at the entry

Because there is no curb, the way the shower is enclosed matters. The guide says a shower curtain is economical and does not block a person using a mobility device. To seal well, the curtain must be sized to the opening and touch the floor just inside the entry. Curtains with small weights sewn into the lower seam help keep that seal.

Shower doors with a rubber flange at the bottom can seal better than curtains. The guide says the trackless type is the only viable option, because a frame can be stepped or rolled over. Doors should swing or fold out of the space where a person needs to maneuver.

For full-width access, the guide says the state code and national standards require the full width of the opening to be available for entry. If doors are used, a pair of folding or swinging doors creates a full-width entry. The guide notes that an opening of 32 inches clear could work, but 36 inches is easier to turn through and is the preferred size.

A secondary drain outside the shower can catch overflow, especially in a narrow stall. The guide says to avoid an institutional look and to keep the floor slope inside and outside the shower as small as possible. A trench or trough drain along the opening can give a truly flush entry. The guide notes that a few prefabricated shower units now include one.

Flexible dams and removable dams are also described. The guide calls them backup solutions, not the main method of water control. Flexible dams wear out over time and must be replaced, and some wheelchair users cannot roll over them. Semi-permanent dams are not allowed when strict code compliance applies.

Plan for grab bars and a seat

The guide recommends reinforcing the whole wall around bathing fixtures, not only the minimum areas named in accessibility standards. Reinforcing added during construction lets grab bars be mounted later without removing the wall surface. For custom walls, the guide specifies plywood reinforcing at least 3/4 inch thick, let in between framing or applied over studs.

Prefabricated units are harder to reinforce after installation. The guide says many older and current residential models were not engineered for it, and that gaps between the fixture and the framing make it hard to fit reinforcing snugly. It suggests choosing newer models with flat walls that can take factory-installed reinforcing. The guide says some manufacturers will install broad reinforcing panels on qualified units if requested. For more on grab bar options, see our comparison of Ravinte and Gotega grab bars.

A seat mounted to the wall is more stable than a free-standing chair, and folding seats can rest against the wall when not in use. The guide says the seat needs its own reinforcing, and that the forces of getting on and off must be planned for. Where a seat is provided in a standard roll-in compartment, the guide says it should be a folding type, installed on the side wall next to the controls. For seat options, see this comparison of shower seats and transfer benches.

The guide also says that for grab bars, use rust-resistant stainless steel screws, drill a shallow pilot hole with a larger bit so the screw does not crack the finish, and seal every fastener penetration through the shower surface with silicone caulk.

Check the work before tile and the enclosure go in

Before the surround is closed up, check that the floor slopes toward the drain, that no threshold stands at the entry, that the membrane runs without breaks into the walls and onto the adjacent floor, and that reinforcing is in place wherever a grab bar or seat will go. The guide says that if a few critical details are handled, curbless showers can meet building codes and avoid leaks. That is the guide’s claim, and it covers only the details it describes.

Common mistakes to avoid

Setting the shower on the subfloor and building up the room floor, which leaves a level change at the door.
Choosing a prefabricated unit marketed as accessible that still has a threshold.
Relying on a flexible or removable dam as the main way to hold water.
Leaving gaps in the membrane at the walls or the floor edge.
Skipping the reinforcing, so grab bars or a seat cannot be mounted securely later.
Choosing a framed door that a wheelchair must roll over.

Safety, water shutoff and when to hire a pro

Shut off the water supply before cutting into any wall, floor or fixture, and confirm the water is off before you start. Valve, drain and waterproofing work belongs to a licensed plumber or contractor. Changes to joists or a slab are structural work, and the guide’s custom-build notes stress careful detailing and supervision. A permit may be required by your local building department. Codes vary by state, city and building type. The sources here cite a North Carolina code, federal accessibility standards and general design practice, not your local code.

What we could not verify: what the sources do not say

The sources do not give labor, material or total project figures, and they do not name brands of membrane, drain, base or enclosure. The San Diego booklet is dated 2003, and it refers to the North Carolina accessibility code and the ADA Standards for Accessible Design. It does not cover your state or city code. It does not give a required recess for every floor type, and it does not describe how to frame a floor of a particular span. The Access Board text quoted here applies to certain facility types, such as facilities with more than 50 beds that provide common use bathing. It does not set a rule for single-family homes. Neither source covers permit steps or inspection timing.

Points that rest on one source only: the 30-by-60-inch minimum, the 36-inch minimum depth, the 42-inch and 48-inch depths, the 5-foot-by-5-foot attendant size, the recess depth, the tile slope, the membrane height at the drain, the two-stage drain, the prefabricated base warnings, the trench drain and the grab bar fastener advice all come from the San Diego booklet alone. The Access Board text supports the roll-in seat rule, the transfer-type rule and a half-inch maximum threshold for roll-in compartments. That threshold limit conflicts with the San Diego booklet’s statement that thresholds are prohibited.

FAQ

Is a walk in shower the same as a roll-in shower?

Both terms describe a shower with no curb at the entry. The San Diego guide uses “curbless” as its main term, because it says “roll-in” suggests the shower only helps wheelchair users. The guide also says curbless showers help many people who do not use wheelchairs.

Does the shower floor need a slope?

Yes. The guide says the shower floor must slope toward the drain and away from the entry, so water does not flow out of the stall. Its tile floor drawings show a slope of 1/8 inch to 3/16 inch per foot for custom units.

Can a walk in shower have any threshold at all?

The two sources disagree. The San Diego booklet says the state code and the ADA Standards prohibit thresholds at curbless showers, and it describes a half-inch threshold as acceptable only in specific retrofit cases. The Access Board text opened sets a half-inch maximum threshold for roll-in type shower compartments. Your local code decides which rule applies to your project.

Can a shower curtain replace a door?

The guide says a curtain is economical and does not interfere with a wheelchair user’s movement. It must be sized to the opening, touch the floor just inside the entry, and have small weights in its lower seam to keep the seal. A trackless door with a rubber flange at the bottom can seal better than a curtain.

Do I need to reinforce the walls for grab bars?

The guide recommends reinforcing the whole wall around the shower, not only the minimum areas named in accessibility standards. If you plan a wall-mounted seat, the guide says the seat also needs reinforcing. Reinforcing is easiest to add during construction.

Can I do the installation myself?

The sources do not address who may legally do this work. The guide says the trades must coordinate closely, and it calls for a qualified builder or engineer for structural changes. Valve, drain and waterproofing work should go to a licensed plumber or contractor, and your local building department can tell you about permits.

Bottom line

A walk in shower works when the floor slopes to the drain, the entry stays flush with the room floor, and the waterproofing is continuous. Plan water control first, then the wall reinforcing for grab bars and a seat. Shut off the water before any cutting, and check your local code before you change the floor.

Sources

U.S. Access Board, ADA Accessibility Standards: https://www.access-board.gov/ada/ (opened 2026-10-27)
City of San Diego, Curbless Showers: An Installation Guide (NC State University Center for Universal Design, 2003): https://www.sandiego.gov/sites/default/files/legacy/development-services/pdf/industry/udcurbless.pdf (opened 2026-10-27)