Shower Curbs in Florida: Threshold & Slope by Code.

How High a Shower Curb Must Be

A Florida shower curb must stand at least 2 in. above the top of the drain and no more than 9 in., measured from the top of the curb down to the drain. That single rule, from the plumbing-fixtures chapter the FBC shares with the model codes, sets the minimum dam that keeps shower water from running out onto the bathroom floor.

Most homeowners picture the curb as a fixed-height block of concrete. It is better understood as a relationship: the code cares about how far the high point sits above the drain, not how tall the framed step is on its own. Because the pan slopes downhill to the drain, part of that 2 in. is already earned by the slope before the curb is even built.

What the code section actually says

The governing language lives in Section P2709 of the Florida Building Code, Residential, which mirrors the International Residential Code. It states the curb shall be not less than 2 in. and not more than 9 in. deep measured from the top of the curb to the top of the drain, and that the receptor walls must finish at least 1 in. above the curb. Both numbers exist to contain water, not to dictate a comfortable step height.

Curb above drain

2 in. minimum, 9 in. maximum, top of curb to top of drain (FBC Residential P2709).

Walls above curb

The receptor sides and back finish at least 1 in. above the curb so splash cannot escape behind the tile.

Finished step height

Typically lands 2-6 in. at the threshold once the floor slope and tile thickness are added.

Why a framed curb can read under 2 in.

Inspectors measure to the drain, so a curb framed only 1.5 in. above the pan edge can still pass when the drain is set deep enough that the high point clears 2 in. The slope does the rest of the work. This is the detail that confuses do-it-yourself rebuilds: the curb is short, the assembly still complies, and the geometry hinges on where the drain sits.

The Slope the Floor Needs to Drain

The shower floor must fall 1/4 in. per foot — a 2% grade — toward the drain from every direction. That pitch is the published minimum across the IPC, the IRC, and the TCNA Handbook, and the IRC also caps the maximum at 1/2 in. per foot so the floor is neither flat nor steep enough to feel unstable underfoot.

Below 1/4 in. per foot, water loses the gravitational pull it needs to overcome surface tension on tile and grout, and the low spots hold standing water long after the shower is off. In a humid, slab-on-grade Florida bathroom, that lingering water feeds mildew in the grout and biofilm at the drain — the visible symptom of a pan that was set too flat.

Reading the pitch in real units

The math is easier than it sounds. Multiply the run from the wall to the drain, in feet, by 1/4 in. to get the total fall. The further the drain, the more vertical drop the pan needs, which is why a large shower demands a taller buildup at the perimeter.

• 2 ft run: about 1/2 in. of fall from wall to drain.
• 3 ft run: about 3/4 in. of fall.
• 4 ft run: about 1 in. of fall.
• 5 ft run: about 1-1/4 in. of fall at the perimeter.

Those figures are why a center-drained shower in a wide Florida master bath needs a thicker mortar bed at the walls than a compact guest stall — the longer the run, the more buildup the slope requires.

Center drain vs offset drain

A center drain splits the run in half, so each wall only travels half the distance and the perimeter buildup stays low. An offset drain near one wall lengthens the run from the far wall, which raises the buildup and the curb height on that side — a trade worth weighing before the drain is roughed in.

Slope is measured on the tile, not the liner

The finished, walkable surface is what has to meet 1/4 in. per foot. If only the buried liner is sloped and the mortar above it sits flat, the tile ponds even though a hidden layer drained correctly. The pitch has to carry all the way up through the bed to the tile the homeowner stands on.

Why the Threshold Sits Above the Drain

The threshold has to sit above the drain because it is the spillway: water rises only to the lowest exit, so the entry point must be the highest edge of the pan. Code fixes that height difference at 2 in. minimum between the top of the curb and the top of the drain, guaranteeing a 2 in. reservoir before water can ever reach the doorway.

Think of the pan as a shallow basin. The drain is the bottom outlet; the curb is the rim. If the rim were level with or below the outlet, a slow drain or a dropped washcloth over the strainer would send water straight across the threshold and into the room. The 2 in. margin is the buffer that absorbs a partial clog or a heavy rainfall-style showerhead.

Where the bathroom floor fits in

Beyond the shower, the bathroom floor outside a curbless entry should also pitch slightly back toward the shower or a secondary drain so any overflow returns to a drained surface. On Florida slab-on-grade this is handled in the pour or the leveling layer, and it is the reason a true curbless build is a slab-recess decision made before tile, not a finish detail.

The strainer is part of the math

The 2 in. reservoir assumes the drain strainer is clear. A grate clogged with hair effectively raises the water line, so the margin that keeps water off the bathroom floor shrinks in daily use. This is why the code minimum is a floor, not a target — a well-built pan banks extra reservoir for the inevitable partial clog.

Curb vs Curbless: Two Code Paths

A standard curb and a curbless entry answer to different rules. A curbed shower follows the 2-in.-above-drain dam rule; a curbless or accessible shower replaces the curb with a recessed slab and a threshold capped at 1/2 in. under ICC A117.1. The accessible path trades the tall dam for a wider, deeper slope and often a linear drain.

The accessible threshold cap

Roll-in and transfer-type compartments built to ICC A117.1 allow a threshold of 1/2 in. maximum, and any change in level over 1/4 in. up to 1/2 in. must be beveled at a slope no steeper than 1:2. The U.S. Access Board ADA guidance for bathing rooms uses the same ceiling. Half an inch is the entire reservoir an accessible shower gets.

Roll-in vs transfer thresholds

A roll-in compartment is sized for a wheelchair to enter fully, while a transfer compartment is built for someone to sit and slide in from a seat; both share the 1/2 in. threshold cap, but the transfer type permits a vertical edge up to 1/4 in. before the 1:2 bevel is required. The use case, not the look, picks between them.

The tolerance that makes it hard in Florida

Here is the squeeze. With a 1/2 in. high point and a 4 ft run to the drain, a 1/4-in.-per-foot pan would want roughly 1 in. of fall — more than the threshold allows above the bathroom floor. The build resolves this by recessing the slab so the drain drops below the surrounding floor level, letting the pan hit full slope while the entry stays at 1/2 in. That recess is poured-in, not patched on.

Most Florida bathrooms can go either way; the deciding factor is whether the slab can be recessed for the drain, which is why our crews settle the walk-in shower entry type before a single tile is set.

How the Pan Is Actually Sloped

A durable Florida shower pan is sloped twice: a built-up pre-slope under the waterproofing, then the finished bed above it, both running 1/4 in. per foot to the drain. Skipping the pre-slope is the single most common cause of a pan that drains at the tile but holds water against the membrane below.

The build sequence, step by step

The flood test is non-negotiable in a humid climate: it is the only proof the membrane and pre-slope move water to the drain before tile permanently hides the assembly. We document each tiled shower floor at this stage.

Pre-slope vs single flat bed

Whether the slope is hand-floated or a molded foam tray, the rule is the same: the layer the water touches first has to fall toward the drain, or the pan ponds where no one can see it.

The Florida Slab That Complicates It

Florida builds on slab-on-grade, and a poured slab is rarely dead flat or perfectly level — small dishes and high spots are normal. When a shower pan only has 1/2 in. to 1 in. of total fall to play with, an out-of-plane slab can eat the entire slope tolerance, which is why the pan is built up rather than tiled directly on the concrete.

Flatness eats the tolerance

A slab that dips 1/4 in. across the shower footprint has already consumed a quarter of the fall a 1 ft run is supposed to provide. The pre-slope corrects this by establishing the grade in mortar, independent of the slab's imperfections, so the drainage plane is true even when the concrete under it is not.

Humidity raises the stakes

In a climate with high year-round indoor humidity, a pan that ponds never fully dries between uses. Standing water at a flat spot becomes a permanent damp zone that stains grout and grows mildew at the threshold. The slope is not cosmetic here; it is the mechanism that lets a Florida shower dry out. A pan that drains and a pan that ponds look identical the day the tile goes down.

Why grout cleaning never fixes it

Homeowners often attack a ponding low spot with new grout or sealer, but the water is held by geometry, not by porous grout. Until the bed under the tile is re-pitched to 1/4 in. per foot, the same puddle returns after every shower. The repair is structural — a new pre-slope — which is why a cosmetic refresh cannot solve a drainage defect.

When an older shower ponds, the fix is almost never new grout — it is a rebuilt pre-slope, which is the core of any honest shower remodel on a Florida slab.

Curb and Slope Numbers at a Glance

The whole assembly comes down to a short set of dimensions that an inspector checks and a homeowner can verify. Each one exists to keep water moving to the drain and inside the pan.

The checklist an inspector runs

1. Floor slope: 1/4 in. per foot to the drain, confirmed on the finished tile.
2. Curb height: top of curb 2-9 in. above the top of the drain.
3. Wall height: receptor sides and back finish at least 1 in. above the curb.
4. Accessible threshold (if applicable): 1/2 in. maximum, beveled 1:2 above 1/4 in.
5. Pan integrity: 24-hour flood test holds water before tile.

Run that list against any quote and against any finished shower; if a single line is missing, the assembly is not yet code-and-climate ready for a Florida bathroom. The full bathroom remodeling scope, and the tile work over the pan, both depend on these five numbers being right first.