Large Format Tile Ensuite Renovation — Glebe, Ottawa

The Challenge: A 1960s Ottawa Home and Large Format Tile

The homeowners in Ottawa's Glebe neighbourhood had a clear vision: a clean, contemporary ensuite with large format porcelain throughout, in-floor heating, and a curbless walk-in shower with a linear drain. The challenge was that their home was built in the early 1960s — which meant a floor system that had settled unevenly over six decades and a subfloor that measured significantly out of flat by the time we assessed it.

Large format tile in the 24×48 range requires flatness within 1/8 inch over 10 feet, with no more than 1/16 inch variation over 24 inches. The existing floor failed this requirement by a meaningful margin — up to 3/8 inch of variation across the bathroom floor. Installing 24×48 tile directly over that substrate would have produced visible lippage at tile edges throughout the room.

Substrate Levelling Before Anything Else

The full floor was addressed with a floor-levelling compound, applied in two passes to bring the high and low points into tolerance. This added a full day to the project before tile work could begin, but it was non-negotiable for large format tile to look correct.

The walls were assessed separately. Standard 1/2-inch drywall on the shower walls had enough flex that we replaced it with cement board for the shower enclosure walls, which are straighter and provide a far better substrate for the large format wall tile in portrait orientation.

Schluter DITRA-HEAT for the Floor

For in-floor heating beneath large format tile, we used Schluter DITRA-HEAT — an uncoupling membrane with integrated channels for the electric heating cable. DITRA-HEAT serves two purposes simultaneously: it provides the uncoupling layer that allows the subfloor to move slightly without transmitting that movement to the tile, and it houses the heating cable in a consistent, protected plane below the tile.

The heating cable was laid in the DITRA-HEAT channels across the full bathroom floor, with an in-slab thermostat sensor positioned mid-floor for accurate temperature reading. The DITRA-HEAT membrane was bonded to the levelled concrete subfloor with unmodified thinset before the heating cable was installed.

For large format tile over a heated floor system, the thinset specification matters: we used a large-format, non-sag thinset rated for use over heating cables, applied to both the DITRA-HEAT surface and back-buttered onto each tile to achieve the required 95% coverage without voids over the cable.

Shower Waterproofing and Linear Drain

The shower enclosure was waterproofed with Schluter KERDI membrane — continuous across all walls and the floor pan, with KERDI-BAND reinforcing all inside corners and transitions. The linear drain was positioned along the far shower wall, requiring the floor to slope uniformly from the opposite wall toward it at 1/4 inch per foot — a different mortar bed setup than a centre-drain shower.

Getting consistent single-direction slope with large format tile requires careful planning at the layout stage. The 24×48 tiles were oriented with their long dimension parallel to the slope direction, which keeps the tile edges as level as possible across the fall and minimizes the visual effect of the pitch.

Flood test passed before any tile was set in the shower. 24 hours of standing water, then a thorough check of all transitions and penetrations.

Tile Installation: 24×48 Throughout

The 24×48 porcelain was installed in a stacked horizontal pattern on the shower walls and in a large offset pattern on the bathroom floor. Both orientations were laid out from the centre of each surface to ensure no slivers at edges — on large format tile, a sliver at the wall is much more visually disruptive than on smaller tile.

Every tile was back-buttered in addition to combing the substrate. On 24×48 tile, this is the only reliable way to hit 95% thinset coverage — combing the substrate alone leaves ridges and voids across a surface large enough to be a structural issue over time. Tile levelling clips were used throughout at 12-inch intervals along tile edges to maintain consistent plane across the floor and wall installations.

Movement joints — filled with colour-matched silicone, not grout — were placed at all changes of plane, at the perimeter of the bathroom floor, and at the transition between floor and shower walls. In an Ottawa home where seasonal temperature swings can be substantial, these joints absorb the thermal expansion that would otherwise crack the tile or grout.

The Results

The finished ensuite features continuous 24×48 porcelain from floor to ceiling in the shower and across the bathroom floor, a seamless transition at the curbless shower entry, and a linear drain that's visible as a clean horizontal element against the back wall. The in-floor heating covers the full bathroom floor area including the transition zone outside the shower.

From the substrate work to the final grout, the project took nine days. The extra day for floor levelling at the start meant the tile installation itself was straightforward — no improvising around a substrate that wasn't ready.