According to the "Building Code of Australia" a Habitable Room is:

" a room used for normal domestic activities and

Includes a bedroom, living room, lounge room, music room, television room, kitchen, dining room, sewing room, study, playroom, family room, home theatre, and sunroom, but

Excludes a bathroom, laundry, water closet, pantry, walk-in wardrobe, corridor, hallway, lobby, photographic darkroom, clothes drying room, and other spaces of a specialised nature occupied neither frequently nor for extended periods."

"A room or space within a building must have sufficient height suitable for the intended function of that room or space." "The requirement is satisfied if the ceiling height is not less than -
In a class 1, 2 or 3 building a habitable room excluding a kitchen - 2.4 meters & in a kitchen, laundry or the like - 2.1 meters and in a corridor, passageway or the like 2.1 meters."

According to BCA Vol 2 part 3.8.2, ceiling heights must not be less than:

• in a habitable room excluding a kitchen - 2.4 m and
• in a kitchen - 2.1m and
• in a corridor or passageway etc - 2.1m and
• in a bathroom, shower room, laundry, sanitary compartment, pantry, storeroom, garage, car parking area etc - 2.1m and
  
• in an attic, room with a sloping ceiling or projection below ceiling line or non-habitable room or similar - a height that does not unduly interfere with the proper functioning of the room or space and
  

• in a stairway - 2.0m measured vertically above the nosing line.

Otherwise, the room would be deemed to be a "utility room".