curbless-shower-drain-guide

As an Amazon Associate we earn from qualifying purchases.

A curbless shower drain is the drain in a shower with no raised curb, where the floor runs level into the wet area. Drainage in that setup depends on the floor slope, the drain position and the threshold at the entry. This guide explains what two sources say on the topic: the 2010 ADA Standards for Accessible Design, which set rules for roll-in showers, and the 2021 International Plumbing Code, which sets slope rules for drainage piping. Both sources are useful, but neither gives a full answer on shower-floor drainage. We say where the gaps are.

Quick answer

• The 2010 ADA Standards say a shower with no curb can give more room to maneuver, and they set minimum sizes for roll-in shower compartments. The standard roll-in size is 30 inches wide by 60 inches deep, measured as clear interior dimensions.
• For a roll-in shower, the threshold at the entry must be 1/2 inch high at most. This is the only threshold height the standards give for roll-in showers.
• The plumbing code’s slope rule covers horizontal drainage piping, not the floor of a shower. It does not state a shower-pan slope, so this article gives none.
• The sources do not give a floor slope, a drain size or a drain location for a curbless shower. Those figures are listed under what we could not verify.

How we chose this topic

People often ask how water stays inside a shower that has no curb. The answer depends on several parts of the job. The floor pitch, the drain, the waterproofing and the entry threshold each matter. We chose two sources that cover different parts of that job. The first is the federal accessibility standard, the 2010 ADA Standards for Accessible Design, which governs the size and entry of roll-in showers. The second is the International Plumbing Code 2021 as adopted in Utah, which governs horizontal drainage piping.

These two sources come from separate families. The ADA Standards are a federal accessibility document. The plumbing code is a model code used by states and cities. The ADA text is also used in building codes that reference it, so a building code could repeat the same accessibility rules. We did not count the ADA text and a building-code reprint as two sources. Our second source is the plumbing code, which covers a different subject.

We did not use a retailer, a product page or a remodeling forum for any claim here. We did not name any shower base, drain or tray. Each quoted phrase was checked word for word against the saved source text.

What the ADA Standards say about curbless showers

Section 608 of the 2010 ADA Standards covers shower compartments. The first point is in an advisory note, which says: “Shower stalls that are 60 inches (1525 mm) wide and have no curb may increase the usability of a bathroom because the shower area provides additional maneuvering space.” An advisory note explains intent. It is not a mandatory rule, but it shows why a curbless design is treated as an accessibility feature.

The mandatory size rule for a roll-in shower reads: “Standard roll-in type shower compartments shall be 30 inches (760 mm) wide minimum by 60 inches (1525 mm) deep minimum clear inside dimensions measured at center points of opposing sides.” The standard also requires a 60 inch wide entry on the face of the compartment. These figures set the room a wheelchair user needs to enter and turn in the shower.

A second standard covers the alternate roll-in shower, which is 36 inches wide and 60 inches deep, with a 36 inch wide entry at one end of the long side. The standard gives both sizes, so a shower that meets one of them is in the roll-in family. The sources do not say which size a particular home should choose.

The threshold rule

The threshold is the part of the floor where a shower meets the bathroom. For a roll-in shower, the standard is direct: “Thresholds in roll-in type shower compartments shall be 1/2 inch (13 mm) high maximum in accordance with 303.” The same section sets a different rule for transfer showers, where the threshold must also be 1/2 inch high at most and must be beveled, rounded or vertical. An exception allows up to 2 inches in some existing transfer showers, but the text we saved limits that exception to existing facilities.

The threshold rule matters for drainage because the floor has to slope toward the drain while the entry stays under the height limit. The standard sets the height at the entry. It does not tell a builder how much slope the shower floor should have to move water to the drain.

Grab bars and controls

The standard also requires grab bars in roll-in showers. Where no seat is provided, grab bars go on three walls, and each bar is installed 6 inches at most from the adjacent walls. Controls and the shower spray unit must sit above the grab bar but no higher than 48 inches above the shower floor. These rules are about access, not drainage, and they do not affect the drain location. Still, a builder placing a drain should keep the wall layout in mind, because the bars and controls set the space around it.

What the plumbing code says about drainage

Chapter 7 of the 2021 plumbing code covers sanitary drainage. Section 704.1 is titled “Slope of Horizontal Drainage Piping,” and it reads: “Horizontal drainage piping shall be installed in uniform alignment at uniform slopes.” The section then refers to a table of minimum slopes by pipe size. The table is in the saved text, but its values did not come through in the text we saved, so this article does not state them.

This section governs the pipe that carries water away from the drain. It is about the drain line beneath the floor, not the slope of the shower floor above it. A shower pan that slopes well but drains into a poorly pitched pipe will still drain slowly. A well-pitched pipe will not help a floor that is level or pitched the wrong way.

The code also covers defects in drain piping. In its discussion of video surveys and relining, the text says that defects include “backgrade or insufficient slope.” Backgrade means the pipe was laid with a reverse or flat grade. Insufficient slope means the pipe does not fall enough to carry waste. The saved text does not say how to test for either problem, so treat that as the point at which a plumber should look at the line.

How the two sources fit together

The two sources cover different parts of a curbless shower. The ADA Standards set the size of the compartment, the width of the entry, the threshold height and the grab-bar and control layout. The plumbing code sets the slope of the drain piping that receives the water. Neither source sets the floor slope of the shower pan, the location of the drain within the floor, or the waterproofing behind the tile.

In practice, a curbless design has to meet the threshold height at the entry, keep the floor sloped toward the drain, and connect to a drain line that is pitched correctly. The sources support the first and third parts. The middle part, the pan slope and drain location, is outside both sources.

What this means for a homeowner

A homeowner comparing shower designs can check three things against the sources. The entry should meet the 1/2 inch threshold limit if the shower is a roll-in type. The compartment should meet the clear-size figures if the goal is roll-in access. And the drain connection should be inspected by a licensed plumber for pitch. The sources do not tell a homeowner how to judge the floor slope by eye.

Common problems the sources point to

The threshold and drain are the two places a curbless shower can fail. A threshold above 1/2 inch in a roll-in shower does not meet the standard, which can matter for a user with a wheelchair or walker. A drain line with insufficient slope or backgrade can leave standing water, and the code treats those as defects to be repaired.

The ADA advisory on maneuvering space also points to a practical issue. A shower with no curb gives more room outside the water, which helps a user move. It does not, by itself, keep water in the shower. That job belongs to the floor slope, the drain and the wall and floor waterproofing, and the sources do not describe the waterproofing.

What we could not verify

• The floor slope a curbless shower pan should have toward its drain. Neither source gives a shower-pan slope.
• The drain size, drain type or drain position for a curbless shower. The sources do not describe shower drains.
• The minimum slope values in the code table for horizontal drainage pipe. The table did not come through in the saved text, so we do not state values.
• How to waterproof a curbless shower floor and walls. Neither source covers waterproofing.
• Local amendments. The plumbing code text we saved is a state adoption, and cities may amend the rules.
• Whether a given curbless shower meets the ADA size rules in a particular building. The standards apply to covered facilities, and this article does not decide that for any building.

FAQ

Does the ADA require a curbless shower?

The text we saved does not require a curbless shower. It sets rules for roll-in and transfer showers, including size, threshold and controls. A curbless design can meet a roll-in rule, and the advisory note says a shower with no curb can increase usability. The standard does not say every shower must be curbless.

How high can a roll-in shower threshold be?

For a roll-in type shower compartment, the 2010 ADA Standards set the threshold at 1/2 inch high at most. The same limit applies to transfer showers, which must also be beveled, rounded or vertical.

What slope does a shower floor need?

The sources do not give a shower-floor slope. The plumbing code section we read covers horizontal drainage piping, not the shower pan. A plumber or the shower-base manufacturer’s instructions should set the floor slope.

Does the plumbing code cover the shower drain?

The section we read covers horizontal drainage piping and its slope. It does not cover the shower drain fitting itself, and it does not state how a curbless drain should be placed.

What is the smallest roll-in shower size in the standard?

The standard roll-in shower is 30 inches wide by 60 inches deep, measured as clear interior dimensions. The alternate roll-in shower is 36 inches wide by 60 inches deep.

Bottom line

A curbless shower depends on three things that the sources only partly cover. The ADA Standards set the roll-in size, the entry width and the 1/2 inch threshold limit. The plumbing code sets the slope of the drain piping. The floor slope of the shower pan, the drain location and the waterproofing are not in either source. Use the standards for the room and the threshold, and have a licensed plumber confirm the pitch and the drain connection before tile goes down.

Sources

• U.S. Access Board and U.S. Department of Justice, 2010 ADA Standards for Accessible Design, Section 608 Shower Compartments and Section 303 Changes in Level. https://www.ada.gov/regs2010/2010ADAStandards/2010ADAstandards.htm (opened 2026-10-28)
• International Plumbing Code 2021, Chapter 7 Sanitary Drainage, as adopted in the Utah Plumbing Code 2021, reproduced on UpCodes. https://up.codes/viewer/utah/ipc-2021/chapter/7/sanitary-drainage (opened 2026-10-29)