The tub used to be fine. Now it's tall and slippery, and watching someone you love lift a leg over the side of it has started to make your stomach drop. You've seen the photos of showers where the tile runs straight from the bathroom floor into the shower with nothing to catch a toe on. One homeowner on r/HomeImprovement wrote down exactly what you want: "No lip if at all possible. Wide enough for wheel chair entry if that ever becomes necessary."
Then you remember the house sits on a concrete slab, like nearly every house in Allen, and you start to wonder if that rules it out.
It doesn't. A shower with no lip can be built on a slab, and we build them. The slab does decide how it gets built, though, and in a lot of Allen homes it decides a little more than people expect.
Why a Shower Has a Lip in the First Place
The curb on a regular shower is there to hold water in. The shower floor slopes down to the drain, and the curb is the wall that keeps whatever doesn't make it to the drain from running out onto the bathroom floor.
Take the curb away and the slope has to do all that work by itself. That means the shower floor needs to sit a little lower than the bathroom floor, so the high edge of the shower meets the bathroom tile at the same height and everything inside runs downhill to the drain. On a house with a wood floor and a crawlspace, a carpenter can drop the framing under the shower to make that room. On a slab there's nothing underneath to drop. The concrete is the floor.
So on a slab you get two ways to make that low spot. You can take the concrete down where the shower goes, or you can bring the rest of the bathroom floor up.
Cutting the Slab or Raising the Floor
Cutting is the cleaner result when the slab allows it. The usual approach, as one person described it, is "cutting away the existing slab where the shower will go and re-pouring so I am left with a recessed area for the preslope, liner, mortar bed, and tile." You end up with one continuous floor and no transition at all. Since the drain is under that same concrete, this is also when the drain gets moved to where the new shower needs it.
Raising the floor works when cutting doesn't. We build the bathroom floor up by an inch or so with a mortar bed or a new underlayment, then slope the shower down to the original slab level. The catch is the bathroom doorway. The raised floor has to meet the hallway somewhere, so there's a small tapered transition at the bathroom door instead of a lip at the shower. For someone with a walker that's usually fine, because a gentle bevel at the door is a very different thing from a curb they have to step over while wet. For a wheelchair, we'd plan that transition carefully and keep it as low and gradual as we can.
Which one we'd recommend comes down to the next question more than anything else.
Check for a Post-Tension Slab Before Anybody Cuts
A lot of homes around Allen, especially in the newer subdivisions, are built on post-tension slabs. North Texas clay swells when it's wet and shrinks when it's dry, and builders run steel cables through the slab and pull them tight so the whole foundation moves as one piece. Those cables are under serious tension. Cutting one weakens the slab and can be dangerous to the person holding the saw.
That's the situation behind a Houzz post that said, flatly, "We have a post tension slab which means it cannot be cut into." That's a reasonable conclusion to reach, and it's the safe default. The fuller answer is that it depends on where the cables are and how deep you need to go. Sometimes the shower area can be scanned, the cables located, and a shallow recess made clear of them. Sometimes the cables run right through the spot and raising the floor is the better answer.
You can often find out what you have by looking in the garage. Many builders stamp a warning into the garage slab near the door, something along the lines of "post-tension slab, do not cut." If you see that, tell whoever you're talking to before they bid the job, because it changes the plan. If you don't see it, that doesn't prove you have a conventional slab, so we check either way.
Straight Answers to the Slab Questions We Hear
How can I DIY install a curbless shower if my home is built on a slab?
On a conventional slab, a handy homeowner can do some of it, but the hard parts are breaking out and repouring the concrete and then waterproofing the whole shower floor so it doesn't leak into the slab, with a drain move somewhere in the middle. On a post-tension slab, don't cut anything until the cables are located. When a DIY curbless shower fails, the slope and the waterproofing are almost always where it started.
Can you do a curbless shower on a post tension slab?
Often, yes, but sometimes not by cutting. If a scan shows the cables are clear of the shower area, a shallow recess may be possible. If they aren't, we raise the bathroom floor and slope the shower down to the existing slab, which still gives you a shower with nothing to step over.
Linear drain vs center drain for curbless shower?
Both work. A linear drain set near the shower entrance or along the back wall lets the floor slope one way, which is easier to walk on and catches water before it leaves the shower. A center drain is simpler to clean. Linear drains do collect hair and soap, so plan on lifting the grate and rinsing it every few weeks.
Keeping the Water in the Shower
There is a trade-off, and it's worth being straight about. One person who loves their curbless shower still said "Minimal to no threshold is great but can get water everywhere," and a Houzz thread describes water that "runs around it and into the bathroom" when the drain wasn't set right. Those are real complaints, and they're why the details matter more on this shower than on any other.
What keeps the water where it belongs is slope that's right all the way to a drain that's in the right place. Length helps as well, since a shower that's long enough keeps the spray from ever reaching the opening. A fixed glass panel on the showerhead side helps a lot without adding anything to step over. Tile choice matters too. One homeowner noticed their tile "had varying thicknesses so it likes to pool in low spots," and on a floor that has to drain well, that kind of thing shows. We set the bathroom floor tile to match, because the bathroom floor will get wet sometimes, and it needs to be a tile that still has grip when it does. Our notes on choosing bathroom flooring go into which tiles hold up to that.
If you need something safer this month while you plan the real shower, a transfer bench and a handheld showerhead make the existing tub workable, and grab bars anchored into the framing help either way. The longer list of aging-in-place upgrades covers those, and if a parent is moving in, we wrote about what has to change in the house before she arrives.
What We'd Do on Your Bathroom
When we come out for a shower like this, the first stop is the garage, looking for that stamp, and then we work out what the bathroom slab is and where the drain runs today. After that we tell you which way we'd build it, cut or raised, and what that means for the bathroom doorway. If someone uses a wheelchair, or might, we size the shower and the opening for that from the start, because it's much easier to build it right the first time than to widen it later.
This is accessibility work we do all over Allen, usually as part of a tub-to-shower bathroom remodel. If someone's balance is the reason you're reading this, say so when you call, because it changes what we'd do first.
If you'd like us to take a look at your bathroom, we do custom work in Allen and across Collin County, and you can reach us at (469) 242-3276.