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Finished floor level (FFL)

FFL is the design height of the finished floor surface, set as an RL on the drawings. Every other building dimension references it. Common defects explained.

By Chalkline. Last updated 14 May 2026. Verified 14 May 2026.

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Finished floor level (FFL) is the design height of the top of the finished floor surface (the tile, the timber, the carpet, the polished concrete) at any given location in a building. It is the datum for every other vertical dimension on the drawings: ceiling height is measured from FFL, window head heights are nominated from FFL, threshold falls run from FFL, and external surface levels are designed below FFL by the contract step-down.

FFL is normally called up on architectural drawings as a reduced level (e.g. “FFL RL 32.450”) and as a relative dimension where the absolute RL is not yet known.

Where FFL drives the build sequence:

  • Site set-out: the surveyor pegs the slab edge at the FFL minus the slab and floor-finish stack-up.
  • Slab pour: the slab top is set so that the floor finish + screed (where used) lands the surface at FFL.
  • Frame: stud heights run from the FFL line, not from the slab top.
  • External works: paving, patios, driveways are designed below FFL by the contract minimum (usually 100 mm to slab edge in habitable areas) so that water flows away.
  • Wet areas: shower floor falls are set so the waste sits below the surrounding FFL and the waterproofing membrane hob heights stand above it.
  • Compliance triggers: bushfire (BAL), flood, and acoustic tests reference dimensions from FFL.

The two common defects. First, FFL confused with slab top. They are different by the thickness of the floor finish (10 mm tile + 6 mm bed = 16 mm). A frame set to slab-top instead of FFL leaves doors short, windows low, and architrave reveals out by the floor stack. Second, FFL set to the wrong reference. The site has multiple benchmarks: the temporary benchmark (TBM), an assumed local datum, the AHD. Setting FFL from a TBM that was bumped or removed mid-job invalidates every height referenced off it. Always re-confirm the TBM RL at the start of each new stage.

Multiple FFLs per build. Splits-level houses, sunken lounges, garage slabs, and verandahs each have their own FFL. The drawings number them (FFL-1, FFL-2 etc.) and the survey set-out should mark each pour to its own line.

Also known as: FFL, finished floor, FF level.

Category: Surveying / set-out / heights.

See also

Last updated: 2026-05-14. Verified: 2026-05-14.

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