How to Spec a Walk-In Shower
That Won't Leak

Most shower leaks I've torn out in Ottawa homes were not caused by bad tile. They were caused by what was under the tile, or what wasn't.

Tile is decoration. Grout is decoration. The waterproofing is the actual shower. If you spec the waterproofing right, the rest is finishes. If you spec it wrong, you're chasing mould inside the wall cavity in five years.

Here's how I build a walk-in shower that lasts.

The 5 spots showers leak

Before we get into materials, you need to know where the water gets in. After 20 years of tearing out failed showers, the same five spots come up over and over:

1. The curb-to-floor transition. Where the shower curb meets the bathroom floor, water finds the seam.
2. The drain flange. If the membrane isn't properly clamped to the drain, water sneaks down the outside of the drain pipe.
3. The corners. Inside corners flex with the building. Mortar and tile crack; flexible membrane corners survive.
4. The valve and shower head penetrations. Every hole through the wall is a potential leak.
5. The bench or niche. Horizontal surfaces hold water. Bad sloping or poor membrane wrap and you've built a sponge.

Every spec choice below addresses one of those five.

Step 1: Pre-slope the floor

The shower floor must slope to the drain at 1/4 inch per foot. That's not optional, and it's not negotiable. Without slope, standing water sits on the membrane until it finds a weakness.

The pre-slope goes under the membrane, not on top of it. I see installers skip this step constantly. They lay the membrane flat on the subfloor, then build the slope on top with thinset and mud. The problem: any water that does penetrate the tile sits in a flat puddle on a flat membrane until it eventually wicks up the wall.

The right sequence: subfloor, dry-pack mortar pre-slope at 1/4" per foot toward the drain, membrane, mortar bed (also sloped), tile.

Step 2: The membrane (this is the actual shower)

I spec Schluter Kerdi on every shower I build. It's an orange polyethylene sheet membrane that bonds to the wall and floor with unmodified thinset. It's bombproof, fast to install, and Schluter publishes the install method publicly so any inspector or homeowner can verify it.

What I won't use:

• Roll-on liquid membranes alone on horizontal surfaces. They work fine on walls, but coverage on a shower pan is hard to verify visually.
• 40-mil PVC pan liners with a mortar bed on top. Old-school, still code-legal, but the mortar bed itself absorbs water. The wall behind the tile gets wet between the membrane and the tile face. Mould loves it.
• Cement board with no membrane. Cement board isn't waterproof. It's water-resistant. Big difference.

"The shower is the membrane. Everything outside the membrane will get wet eventually. Plan for that."

Step 3: The curb (or no curb)

You have two choices: a curbed shower with a low threshold, or a curbless shower flush with the bathroom floor.

Curbless looks beautiful and works for aging-in-place. It also requires the bathroom subfloor to be lowered around 1.5 inches in the shower zone, which means cutting joists or sistering them, which means engineering and a permit. That structural work is a meaningful add to the budget, driven by how much framing has to be reworked and whether an engineer's stamp is needed.

Curbed is simpler. The curb itself must be a single piece of foam or pre-formed Schluter Kerdi-Shower-SC, fully wrapped in membrane. The number-one curb leak I see: contractors stack two 2x4s, wrap them in PVC, then call it done. The 2x4s wick water and rot. Don't do that.

Step 4: Linear drain or centre drain?

Centre drains are cheaper and easier. The floor slopes from four sides into one point. Tile cuts are diamond-shaped and look fine with mosaic but awkward with large-format.

Linear drains let you slope the floor in one direction only, which means you can run 12x24 or 24x48 tiles without rip cuts. They cost more than a centre drain (a quality Schluter Kerdi-Line is several times the price of a basic centre drain) and they require careful joist layout because the drain pipe runs the length of the linear channel.

For a curbless shower, I almost always go linear, placed against the back wall or the entry wall. For a standard curbed shower with mosaic floor tile, a centre drain is fine.

Step 5: Niches done right

Niches are where bad showers turn into bad bathrooms. The niche is a horizontal-ish surface inside a wet zone, and every joint inside it is a leak risk.

How I build a niche:

1. Use a pre-formed Schluter Kerdi-Board niche, not a site-built 2x4 frame.
2. Slope the niche shelf 1/4" toward the front so water drains out, not back into the wall.
3. Use a single-piece slab or a stone shelf, not multiple tiles meeting in the middle. One joint at the front edge is way safer than four joints across the bottom.
4. Membrane wraps inside the niche before tile goes on.

If the layout allows, place the niche on a non-plumbing wall (away from the shower head) and never on an exterior wall in Ottawa. Cold air and humid niche walls equals condensation and mould.

Step 6: Glass spec

For a walk-in shower I spec 3/8-inch tempered glass minimum. 1/2-inch if the glass panel is over 5 feet long or the room calls for it.

Frameless looks cleanest but every joint needs a clear silicone bead, and silicone is the homeowner's responsibility to maintain (replace every 4-5 years). Semi-frameless with a metal channel at the bottom and one corner bracket is more forgiving.

For a true walk-in (no door, just a fixed glass panel), make the panel at least 36 inches wide and angle the shower head so spray hits the back wall, not the open side. Otherwise water finds the floor.

Step 7: Tile and grout

Once the membrane is right, the tile is honestly the easy part. A few rules I stick to:

• Floor tile: mosaic 2x2 or smaller for sloped floors, large-format only with a linear drain.
• Walls: anything you like. 12x24 is the default in Ottawa right now.
• Grout: epoxy grout in the floor, cement grout on the walls is fine. Some installers go full epoxy; it's more forgiving on cleaning but harder to install neatly.
• Silicone, not grout, in every change-of-plane joint. Inside corners, floor-to-wall, wall-to-ceiling. These joints flex; cement grout cracks.

What drives the cost in Ottawa

A properly built walk-in shower in Ottawa, fully waterproofed with Schluter Kerdi, linear drain, niche, and frameless glass, is priced by a handful of cost drivers: the footprint, the waterproofing system, the drain type, the tile size and material, and the glass spec. Curbless adds the joist work on top of all that.

Whatever the number, it's modest next to what a leak costs. Tearing out a five-year-old shower with rotted joists and mouldy drywall behind the tile is far more expensive by itself, before you've rebuilt anything. Spend the money on the membrane, not on the repair. We hand you a detailed written breakdown so you can see exactly which of those drivers is moving your price.

If you're planning a bathroom renovation in Ottawa and you want the shower spec'd right the first time, give us a call at 613-862-4555. Free 48-hour walkthrough. We'll show you exactly where the membrane goes before any tile gets ordered.