In order to determine the correct floor area of a room it must be measured in the following manner:
Take measurements at a point above skirting board level no higher than 1.5m
above the floor.
Room with a sloping roof or ceiling :
The area where a sloping roof or ceiling reduces the height of the room to less than 1.525m (5 feet) this area should not be included when calculating the floor space.
Include area : Subject to any other exclusion, measurement of the floor area should include any floor space formed by a bay window extension, or any area at floor level, which is occupied by fixed cupboards
Exclude area: Subject to any other exclusion, measurement of the floor area should exclude any floor space formed by a projecting chimney breast
Unusable Space: Subject to any exclusion where the space immediately behind the door is no wider than the door itself, this will be considered an unusable space, and will be excluded from the measurement of the floor area of the room. If this space is considerably wider than the door itself, e.g. wide enough to place a wardrobe without a reduction of the circulation space, this space can be included