Curbless shower on a concrete slab: how it is built in a Florida house

A curbless shower on a Florida concrete slab starts with the floor, not the tile. With no curb to hold the water in, the shower floor has to sit lower than the bathroom floor around it and fall to the drain. On a slab-on-grade house that means one of two things: the slab is cut and recessed where the shower goes, or the rest of the bathroom floor is raised to meet it. That choice comes before anyone picks a tile.

This guide walks through both routes, what each one means for your plumbing, your doorways and your waterproofing, and why a linear drain and larger tile are what make a curbless shower read as one continuous floor.

What is a curbless shower?

A curbless shower, also called a zero-entry or walk-in shower, has no curb or step at its edge. The bathroom floor runs straight into the shower, usually behind a fixed glass panel rather than a door. Nothing stops the water at the entry except the slope of the floor, so the slope does all the work a curb used to do.

That is why people want one. There is nothing to step over, the room looks larger, and the floor reads as one surface from the vanity to the back wall. It is also a shower that still works if someone in the house ever needs a walker, a shower chair or a wheelchair.

Why a concrete slab makes curbless harder

A shower floor needs depth. Under the tile there is a sloped bed, a waterproof membrane and the drain body, and the floor has to fall toward the drain all the way from the entry. The usual figure for that fall is a quarter of an inch per foot. In a shower with a curb, all of that sits on top of the bathroom floor, and the curb hides the difference in height.

Take the curb away and the top of the shower floor at the entry can be no higher than the bathroom floor beside it. In a house with a wood-framed floor, the framing under the shower can be dropped. Many Florida houses sit on a concrete slab poured on the ground, so there is no space underneath to drop into. The extra depth has to come from somewhere else.

Option one: recess the slab

The cleanest curbless shower on a slab is built by cutting out the concrete in the shower's footprint and pouring it back lower. The outline is saw-cut, the concrete inside it is broken out, the drain is set at its new depth, and the recess is poured to leave room for the sloped bed and the membrane. The finished shower floor then meets the bathroom floor at the same height, with no step anywhere.

Three things decide whether this is the right route:

• The drain line under the slab. A linear drain, or a drain in a new position, usually means trenching to reach the existing line, so where the old drain sits matters.
• The vapour barrier under the concrete. It is cut along with the slab and has to be patched before the new pour, or ground moisture has a path straight up into the new shower floor.
• The slab itself. Some houses are built on post-tensioned slabs, with steel cables under high tension running through the concrete. Those are not cut until the builder's plans or an engineer show where the cables are.

Cutting a slab is structural work, and structural work can need a permit. We advise on that against Bradenton and Sarasota code as part of the quote.

Option two: raise the bathroom floor

When the slab cannot or should not be cut, the other answer is to build the rest of the bathroom up instead. The shower floor is built on the existing slab with its slope, and the floor outside it is raised to the height of the shower's entry with a levelling layer under the new tile.

It avoids the saw and the trench, but the height has to go somewhere. Every raised inch shows up at the bathroom door, where the new floor meets the hallway, and around the toilet, the vanity and the door swing. A small threshold at the doorway is often the result, which moves the step from the shower to the door. Whether that is acceptable depends on the house and on who the shower is for.

Linear drain or centre drain?

A centre drain needs the floor to slope in from all four sides, like a shallow funnel. That works, but the floor has to be cut into angled planes, and a funnel shape asks for small tile or mosaic that can follow it. It is the reason a traditional shower floor is a grid of small pieces.

A linear drain is a long, narrow channel along one edge of the shower, usually the back wall or the entry. The floor then slopes in one direction only, as a single flat plane. A flat plane can take larger tile, so the same porcelain can run from the bathroom floor straight into the shower without changing size. That is what makes a curbless shower read as one floor rather than a room with a hole in it.

Where the channel goes matters too. A linear drain at the entry catches water before it reaches the bathroom; one at the back wall keeps the slope running away from you as you walk in. Either way, the drain is chosen with the tile, so the channel lines up with the joints instead of cutting across them.

The wet room in a coastal interior in tile and porcelain shows the idea at full size: a glass panel instead of a door, twin rain heads, and a marble-look porcelain floor that runs to a linear drain.

Which tile works on a curbless shower floor?

Larger tile works on a single-plane slope, but there is a limit. A shower floor still has to fall, and each tile has to lie flat on that fall without rocking or leaving one edge sitting proud of the next. A full panel cannot be sloped at all, which is why a panel shower usually pairs large-format porcelain panels on the walls with a smaller tile on the floor.

The floor tile also has to grip when it is wet. Ask for the tile's wet slip figure, the dynamic coefficient of friction, rather than taking the word slip-resistant on trust. The slip-rated porcelains in our bathroom tile collection are chosen for that number first and their look second.

Waterproofing a shower with no curb

A shower is a waterproofing assembly with tile on it, and a curbless one has less margin than most. With a curb, water that splashes past the glass lands on a ledge that is still part of the shower. Without one, it lands on the bathroom floor. So the membrane is lapped up the walls and into the drain, and it is commonly carried out past the entry into the bathroom floor, where water is likely to travel.

We build shower pans to spec and install code-compliant waterproofing systems, following ANSI and TCNA guidelines and the manufacturer's own system for the products used. Systems are not mixed between brands. On the proposal the waterproofing is its own line, because it is the part of the bathroom you will never see and the part that keeps the shower dry behind the tile.

The walls are the familiar part. The membrane goes up them and around any niche, and they take whatever tile the room calls for, from zellige-look to stacked. If you are planning a niche, shower niche height and size covers where it sits and why its corners need care.

How big should a curbless shower be?

Without a curb, the size of the wet area does part of the job. Water spreads from the shower head in every direction, and a fixed glass panel only blocks one side of it. A shower long enough for the spray to land well inside it, with the head aimed away from the open end, stays dry at the entry. A tight one may need a second panel or a door, which takes some of the open feeling away.

This is the conversation to have before the slab is cut, with the layout drawn: where the head goes, where the drain runs, where the glass stops, and where the tile joints land. It is easier to move a line on a drawing than a drain in concrete.

What happens next

Because we sell it and we install it, the layout is agreed with the crew that does the tile installation, and the crew is ours. Come to the showroom in Bradenton to stand in the built wet-room vignettes and take samples home, or call (941) 253-0400. When you are ready, send us your plans for a quote, and we'll walk you through whether your slab should be recessed or your floor raised.