Finished floor level (FFL) — why it matters

Coordinating floor build-ups across rooms and trades

What is FFL?

Finished Floor Level is the final height of the completed floor surface — the top of the tile, including adhesive, screed, and any membranes underneath. It's expressed as an absolute height relative to a building datum (often the structural slab of the ground floor) or as a relative level between rooms.

FFL is the single most important coordination dimension in a tiling project. Get it wrong and doors won't open, thresholds create trip hazards, and drainage doesn't work.

Why tilers must understand FFL

The tiler is often the last trade on the floor. The structural slab is set by the builder, the screed by the screeder, the waterproofing by the waterproofer. Each layer adds height. The tiler must verify that the remaining height — from the top of the screed to the required FFL — matches the tile thickness plus adhesive bed.

If the screed was poured too high, there isn't enough room for the tile. If it was poured too low, the adhesive bed becomes excessively thick (over 6 mm is problematic with standard adhesive). Either situation requires correction before tiling can begin.

Calculating floor build-up

A typical floor build-up from slab to FFL:

• Waterproofing membrane (wet areas): 1-2 mm
• Screed: 40-75 mm (varies by heating system and levelling needs)
• Tile adhesive: 3-6 mm
• Tile: 8-20 mm (ceramic 8-10, natural stone 15-20)

Total: typically 55-100 mm from slab to FFL. The exact number depends on tile thickness — which is why tile selection must happen before screed levels are finalised.

Coordinating across rooms

When two rooms share a threshold, their FFLs must match — or the threshold profile must manage the level change. A bathroom with 10 mm ceramic tiles and a hallway with 20 mm stone tiles need different screed depths to achieve the same FFL. The screed contractor needs this information before pouring.

Drainage falls

Wet room floors must slope toward the drain at 1:80 to 1:40 (12-25 mm per metre). This fall is built into the screed, not the adhesive. The FFL at the drain is lower than at the walls. The tiler must verify that the screeded fall produces the correct FFL at all points — tiles follow the screed surface faithfully.