Our Sydney loft conversion has a raked ceiling, and the certifier says the new bedroom doesn't meet the 2.4 m ceiling height. How is height measured under a sloping ceiling, and what applies over the stair?

Whether the certifier is right depends on how the height was measured. For a room with a sloping ceiling, the test is not the height at every point. It is the height over two-thirds of the floor area, and in an attic the figure is 2.2 m, not 2.4 m. [1]

The minimum heights for a Class 1a dwelling: [1]

• habitable room, excluding a kitchen: 2.4 m
• kitchen, corridor or passageway: 2.1 m
• bathroom, laundry, sanitary compartment, pantry, storeroom, garage or the like: 2.1 m
• stairway, ramp or landing: 2.0 m, measured vertically above the nosing line of the treads or the floor surface

Sloping ceilings. Where a room has a sloping ceiling or projections below the ceiling line: [1]

• a habitable room in an attic needs at least 2.2 m over at least two-thirds of its floor area;
• any other habitable room needs 2.4 m over two-thirds of its floor area;
• a non-habitable room needs 2.1 m over at least two-thirds of its floor area.

The step that gets missed. When working out the floor area for the two-thirds test, any part with a ceiling height below 1.5 m is left out of the calculation entirely. [1] The low edges under the rake don't count against the room, but they don't count towards it either.

Applied to your loft bedroom. Measure the floor area where the ceiling is 1.5 m or higher. If the room is in an attic, at least two-thirds of that area needs 2.2 m; if it isn't, 2.4 m. Where there is no ceiling lining, measure to the underside of the roof or floor above. [2]

Over the stair, the requirement is 2.0 m above the nosing line. [1] With a stair rising into a roof space, headroom is usually tightest right where the stair meets the upper floor, so check it there first.

NSW is on NCC 2022 Amendment 2 until 30 April 2027. The same figures carry into NCC 2025, which also clarifies that threshold ramps are excluded from the 2.0 m stair and ramp figure. [3]