Quick answer
A shower curb is the low raised barrier at the entry of a shower that holds water inside the shower floor until it reaches the drain.
It is built from framing, mortar or a foam form, wrapped in waterproofing and then tiled, or it comes molded into a prefab pan. The model plumbing code sets how tall it must be above the drain.
Quick facts
The key facts about Shower Curb, with sources:
- Job
- Holds water in the shower until it drains 1
- Height rule (2021 IRC P2709.1)
- At least 2 and no more than 9 inches from top of curb to top of drain 1
- Below the sides and back
- The finished curb sits at least 1 inch lower than the other edges of the receptor 1
- Liner rule
- Liner extends at least 2 inches above the finished threshold 1
- Accessible threshold (ADA 608.7)
- 1/2 inch maximum in roll-in showers 3
- Prefab example
- Foam curb 6 inches deep and 4-1/2 inches high, in 38, 48 and 60 inch lengths 4
- Glass on the curb
- Shower glazing below 60 inches above the floor is a hazardous location 2
Key takeaways
- The curb is a dam: it keeps water in the shower until the sloped floor carries it to the drain.
- The 2021 IRC wants the curb 2 to 9 inches above the drain and at least 1 inch below the shower's other edges.
- Most curb leaks come from the waterproofing over and around the curb, not from the tile on it.
- Never fasten through the liner on top of a curb; the code bars nails or holes less than 1 inch above the finished threshold.
- A low or zero threshold is possible, but the floor slope and drain must do all the work.
The shower curb in plain English
Step into most showers and you step over a small ridge. That ridge is the curb. It is the front wall of a shallow tub that is the shower floor. Without it, water would run straight out onto the bathroom floor.
The curb works together with the shower pan, which is the sloped, waterproof floor under the tile. The 2021 International Residential Code (IRC) calls the whole floor assembly a shower receptor and treats the curb as its threshold 1.
On a tiled shower, the curb is usually a short wall of wood, brick or foam that is covered by the same waterproofing as the floor and then tiled on all three faces.
Curbs also hold the glass. Many shower doors and fixed panels sit right on top of the curb, so the curb must be solid, level along its length and sloped slightly inward on top so water runs back into the shower.
How a curb keeps water inside the shower
- It sets the water level. Because the curb top is the lowest edge, it is where water would overflow first. The IRC keeps it at least 1 inch below the sides and back so overflow, if it happens, goes out the front where you can see it 1.
- It gives the drain depth. The 2- to 9-inch rule from curb top to drain top makes the shower a basin deep enough to hold water during a clog, but not so deep it becomes a step hazard 1.
- The floor slopes away from it. The finished floor slopes toward the drain at 1/4 to 1/2 inch per foot (2 to 4 percent) 1.
- The waterproofing wraps it. The liner or membrane runs up and over the curb. On a traditional liner, it must extend at least 2 inches above the finished threshold 1.
- The top sheds water inward. Tilers slope the top of the curb slightly toward the shower so splash runs back in.
- Tile and groutThe finished surface on top and both faces
- Thinset mortarBonds tile to the waterproofing or backer
- WaterproofingLiner or bonded membrane wrapped over the curb
- Mortar, backer or foam formShapes the curb and supports the tile
- Curb coreStacked 2x lumber, brick or a foam curb
- SubfloorSupports the whole assembly
Layer order differs by system: with a traditional liner the waterproofing sits under a mortar bed; with a bonded membrane it sits just under the thinset. Source: [1] [5]
Types of shower curbs
| Curb type | How it is built | Watch for |
|---|---|---|
| Framed wood curb | Stacked 2x lumber nailed to the floor, wrapped in liner and mortar | Fasteners through the liner; wood that gets wet rots |
| Brick or block curb | Masonry set in mortar under the liner | Heavy; slow to build |
| Foam curb (prefab) | Waterproof foam form set in thinset, seams sealed with membrane strips 4 | Must use the system's own membrane and sealing steps |
| Molded curb on a prefab pan | Curb formed as part of an acrylic, fiberglass or composite base | Size must match the opening |
| Low or beveled threshold | A threshold of 1/2 inch or less for access 3 | Floor slope and drain must keep water in |
| No curb (curbless) | Floor recessed so there is no step | See curbless shower for the framing it needs |
Example: checking a curb against the 2- to 9-inch rule
A sample 36 by 60 inch shower with a center drain, checked against 2021 IRC P2709.1. The dimensions are an illustration, not a design 1.
| Check | Sample figure | Result |
|---|---|---|
| Distance from drain to the curb | 18 inches (1.5 feet) | Half of 36 inches |
| Floor slope at 1/4 inch per foot (minimum) | 1.5 × 0.25 = 0.375 inch rise at the curb edge | Meets the 2 percent minimum 1 |
| Floor slope at 1/2 inch per foot (maximum) | 1.5 × 0.5 = 0.75 inch rise | Upper limit of 4 percent 1 |
| Prefab foam curb height | 4-1/2 inches above the floor it sits on 4 | Product dimension |
| Curb top above drain top (with 3/8 inch rise) | About 4-1/2 inches, depending on tile and bed thickness | Inside 2 to 9 inches 1 |
| Side and back walls | Must sit at least 1 inch above the finished curb | Walls are taller, so this passes |
The math shows why a standard curb clears the code easily and why a curbless shower is hard: with no curb, you lose the 2-inch minimum and must use the accessible-threshold path and careful floor design instead. Exact numbers change with the drain, mortar bed and tile thickness, so the installer confirms them on site.
Where the curb shows up in a bathroom remodel
On the design. Your bathroom remodel plan should show curb height, width, length and finish, and which side the glass sits on. The curb width also sets how wide the glass channel or door bottom can be.
In the bid. A clear bid names the curb method (framed, foam or prefab) and the waterproofing system used on it. If a bid only says "tile curb," ask what is under the tile. Our bathroom remodel cost calculator shows what moves the budget for a tiled shower.
At inspection. Many building departments test the shower pan with a flood test before tile goes on. The curb is the dam that holds that test water.
In the warranty. Membrane makers often tie their warranty to using their full system, including their curb and sealing parts 4.
Curb vs no curb: what a curb gives you
Why a curb helps
- A clear water barrier that forgives a slow drain or a hair clog.
- Easier floor design, since the shower floor can sit at subfloor height.
- A solid base for a glass door or fixed panel.
- Meets the IRC basin depth rule directly 1.
What it costs you
- A trip hazard and a barrier for wheelchairs and walkers.
- Another place for the waterproofing to fail if built badly.
- Visually breaks up a large tiled floor.
- Too low a curb with too shallow a slope can let water escape.
Limits of a shower curb
A curb does not make a shower waterproof; the membrane does. The curb only sets the height the water can reach before spilling. If the waterproofing under the tile has a gap at a curb corner, water will reach the framing no matter how tall the curb is.
Curbs also limit access. The 2010 ADA Standards for Accessible Design, which apply to public accommodations rather than private homes, cap the threshold in a roll-in shower at 1/2 inch, and allow a 2-inch threshold in a transfer shower only in existing buildings where a lower one would disturb the slab reinforcement 3.
Owners planning to age in place often borrow those dimensions even though the ADA does not govern their home.
Finally, a curb adds a ledge where water sits if the top is flat. A slight inward slope and a good grout or sealant joint at the glass solve that.
What drives the cost of a shower curb
We do not list prices. The curb is a small part of a shower budget, but these choices move it: framed curb versus a prefab foam curb, the waterproofing system, the tile and how many cuts the curb faces take, a solid stone cap versus tile on top, and the glass.
A curb cap in one piece of stone avoids grout joints on top, which sheds water better, but adds fabrication.
Going curbless is the bigger cost decision, because it can mean recessing the subfloor or framing so the shower floor sits lower. See our remodeling cost guide for what drives bathroom budgets.
Lifespan follows the waterproofing. A curb built on a tested, continuous membrane can last as long as the tile. Ask for the membrane maker's warranty terms and the installer's workmanship warranty in writing.
How a tiled curb is built
Steps vary by system. This is the general order; the membrane maker's instructions govern.
- Plan the curb height and position from the drain height, floor slope and glass design.
- Build the curb core: stacked lumber, masonry or a foam curb set in thinset and pressed down for full support 4.
- Install the waterproofing over the curb. With a liner, keep it at least 2 inches above the finished threshold and do not nail or puncture it less than 1 inch above the threshold 1.
- Seal inside and outside corners with the system's preformed corners or strips 4.
- Flood test the pan and curb if your inspector or the membrane maker requires it.
- Tile the curb with a slight inward slope on top, then install glass without drilling through the waterproofing where avoidable.
Holes in the curb are leak paths
Screws for glass, nails for metal lath or a careless cut through the liner on the curb top let water into the framing. Follow the glass maker and membrane maker together, and fix any leak quickly: EPA advises drying wet materials within 24 to 48 hours to prevent mold.
Caring for a shower curb
- Keep the glass seal intact. Replace worn sweeps and vinyl seals so water stays inside.
- Watch the grout and caulk on top. Cracked joints on the curb cap let water in fast.
- Squeegee the top. Standing water on a flat curb wears grout.
- Look at the floor outside. Damp grout or loose tile outside the curb is an early leak sign.
- Avoid harsh scrubbing on sealant joints. Recaulk instead of digging at mildew.
Warning signs a curb is leaking
- Stains or bubbling paint on the wall or ceiling below the shower.
- Loose or hollow-sounding tile on or near the curb.
- Dark grout that never dries along the curb base.
- Musty smell or visible mold near the shower entry 6.
- Soft flooring just outside the curb.
If you see these, stop using the shower and call a tile or bathroom contractor to find the leak. Fixing it usually means opening the curb, so the sooner the better. EPA says to fix the water problem and dry wet areas within 24 to 48 hours 6.
Shower curb rules: 2021 IRC P2709, R308 and the ADA
Curb dimensions. 2021 IRC Section P2709.1 says a receptor with a finished curb threshold must have the curb at least 1 inch below the sides and back, and 2 to 9 inches deep measured from the top of the curb to the top of the drain.
The floor must slope toward the drain at 1/4 to 1/2 inch per foot 1.
Liners. P2709.2 lists approved linings for site-built receptors, including PVC and CPE sheets and bonded membranes meeting ANSI A118.10, and requires the lining to extend at least 2 inches beyond the rough jambs and at least 2 inches above finished thresholds.
P2709.3 bars nailing or perforating the lining less than 1 inch above the finished threshold 1. TCNA maintains the ANSI A118.10 membrane standard, current as a 2023 edition 5.
Glass. IRC R308.4.5 treats glazing in shower enclosures as a hazardous location when its bottom edge is less than 60 inches above a standing surface, which means safety glazing 2.
Size and doors. P2708.1 sets a minimum shower size of 900 square inches with no dimension under 30 inches, and hinged shower doors must open outward 1.
Accessibility. 2010 ADA Standards 608.7 limits roll-in shower thresholds to 1/2 inch 3. The ADA covers public places, not private homes, but the figures are a useful target for accessible remodels.
Codes are adopted and amended locally; your plumbing inspector has the final word.
Shower curb vs shower pan vs threshold vs curbless
| Term | What it is | Main difference |
|---|---|---|
| Shower curb | Raised dam at the shower entry | Holds water in; 2 to 9 inches above the drain 1 |
| Shower pan | The sloped waterproof floor | Carries water to the drain; the curb is its edge |
| Accessible threshold | A threshold 1/2 inch high or less | Lets a wheelchair roll in 3 |
| Curbless shower | Shower with no step at all | Floor framing is lowered instead |
| Waterproofing membrane | The layer that actually stops water | Must wrap the curb without gaps |
Ask how the curb corners are sealed
The two inside corners where the curb meets the walls are the most common leak points. Ask your installer which preformed corners or patches they use there, and ask to see them before tile goes on.
Shower curb myths
- Myth A taller curb means a more waterproof shower.
- Reality Height only sets the overflow point; the membrane does the waterproofing, and the IRC caps the curb at 9 inches above the drain 1.
- Myth Grout on the curb keeps water out.
- Reality Grout and tile are not waterproof; the liner or membrane beneath does that job 5.
- Myth You can screw glass anywhere on the curb.
- Reality The IRC bars nailing or perforating the liner less than 1 inch above the threshold 1.
- Myth Any low threshold is ADA-compliant.
- Reality The ADA roll-in limit is 1/2 inch, and transfer showers need a beveled, rounded or vertical threshold 3.
- Myth A curb needs no slope on top.
- Reality A slight inward slope sheds splash back into the shower rather than onto the floor.
What changes by state or city
Shower curbs follow the plumbing code your jurisdiction adopts. Some states use the IRC plumbing chapters, others use the Uniform Plumbing Code or their own plumbing code, and the curb and liner rules can differ in detail.
Whether a shower pan flood test is required, and who may install a shower, also vary. Check with your building department, and confirm your contractor holds the license class your state requires before hiring. There is no climate variable for a shower curb.
When the curb should drive your shower design
Think about the curb early if anyone in the house uses a walker or wheelchair, if you plan to age in place, if you want frameless glass, or if your shower drain sits high. Each changes curb height or whether you have one at all.
For most remodels a standard tiled or prefab curb is simple and reliable. For accessibility, compare a low threshold with a full curbless design before demolition starts. Our guide to choosing a contractor lists the questions to ask a tile installer.
- If Everyone in the home steps easily
- Then A standard curb is the simplest, most forgiving choice
- If You plan to age in place
- Then Plan a threshold of 1/2 inch or less, or curbless
- If You want frameless glass
- Then Size the curb width to the glass channel and plan fasteners
- If Your subfloor cannot be recessed
- Then Keep a curb, or use a low threshold with a linear drain
Questions about Shower Curb
How high should a shower curb be?
Under the 2021 IRC, the top of the curb must be 2 to 9 inches above the top of the drain, and at least 1 inch lower than the sides and back of the shower.
Many tiled curbs end up about 4 to 6 inches above the bathroom floor, but the code measures from the drain, not the floor.
Do you need a shower curb?
Not always. A shower can be curbless or have a low threshold if the floor is recessed and sloped to a drain that keeps water in. The IRC curb rule applies where a curb threshold is used. Curbless showers need more careful framing and waterproofing, so plan them before demolition.
How wide should a shower curb be?
Curb width is set by the build method and the glass, not by a code minimum. A common prefab foam curb is 6 inches deep, and tiled framed curbs often end up similar once tile is added. Narrower curbs give less room for glass channels; wider ones take up floor space.
What is a shower curb made of?
A tiled curb is usually made of stacked 2x lumber, brick or block, or a prefabricated foam form, then wrapped in waterproofing and tiled. Prefab shower bases often include a molded curb made of acrylic, fiberglass or composite. Solid stone or quartz is often used as a cap on top.
Why is my shower curb leaking?
Most curb leaks come from gaps in the waterproofing at the corners, fasteners driven through the liner, cracked grout or caulk on the curb top, or a worn glass door seal.
Water can then reach the framing and show up as stains below or outside the shower. A contractor usually has to open the curb to repair it.
Can you put a shower door on a curb?
Yes, most shower doors and fixed glass panels sit on the curb. The curb must be level along its length and solid enough to carry the glass.
Glass in a shower enclosure is a hazardous location under the IRC, so it must be safety glazing. Plan fastener locations so they do not pierce the waterproofing low on the curb.
What is the ADA shower threshold height?
The 2010 ADA Standards limit thresholds in roll-in showers to 1/2 inch. Transfer showers may have a 1/2-inch threshold that is beveled, rounded or vertical, with a 2-inch exception in some existing buildings. The ADA applies to public facilities, but many home remodels use these figures as an accessibility target.
Should a shower curb slope inward?
Yes, a slight slope on top toward the shower is good practice. It sends splash back into the shower instead of letting it sit on the curb or run onto the bathroom floor. A flat or outward-sloping curb top collects water and wears out grout and sealant faster.
Can I replace just the shower curb?
Sometimes, but the curb is tied into the waterproofing of the whole shower floor. Replacing it means cutting back tile and membrane and patching the new curb into the existing system, which some membrane makers do not warranty. Many contractors recommend rebuilding the pan and curb together when the curb has leaked.
Does a shower curb need a permit?
Rebuilding a shower often needs a plumbing or building permit, especially when the drain, pan or liner changes, and some departments require a flood test. Rules vary widely, so check with your building department before work starts.
Sources
- ICC, 2021 International Residential Code, Chapter 27 Plumbing Fixtures (P2708.1, P2709.1–P2709.3), retrieved .
- ICC, 2021 International Residential Code, Chapter 3 Building Planning (R308.4.5 glazing and wet surfaces), retrieved .
- U.S. Department of Justice, 2010 ADA Standards for Accessible Design (608.2, 608.7), retrieved .
- Schluter Systems, KERDI-BOARD-SC prefabricated shower curb, retrieved .
- Tile Council of North America, ANSI Standards (A118.10 waterproof membranes), retrieved .
- U.S. EPA, A Brief Guide to Mold, Moisture and Your Home, retrieved .
Expert review
Written by the HyreRemodel Research team. Not yet reviewed by an outside expert. We say so rather than imply a review that has not happened; see our editorial policy.
How the numbers were checked: Curb, slope, liner and size rules were read from 2021 IRC P2708.1 and P2709.1 to P2709.3, and glazing from R308.4.5, on ICC Digital Codes. Accessible threshold limits come from the 2010 ADA Standards 608.2 and 608.7 on ada.gov.
Prefab curb dimensions and setting steps come from the Schluter KERDI-BOARD-SC product page; membrane standard status from TCNA; mold timing from EPA. The slope example is our arithmetic on code limits for a sample shower. No prices are given.
Suggest a correction. We fix errors and say what changed.