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In Hong Kong Hong Kong law Chapter 123F, Building (Planning) Regulations, Regulation 23 sect 3 sub-paragraph (a) defined that:

Subject to sub-paragraph (b), for the purposes of regulations 19, 20, 21 and 22, the gross floor area of a building shall be the area contained within the external walls of the building measured at each floor level (including any floor below the level of the ground), together with the area of each balcony in the building, which shall be calculated from the overall dimensions of the balcony (including the thickness of the sides thereof), and the thickness of the external walls of the building.
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sub-paragraph (b):

In determining the gross floor area for the purposes of 20, 21 and 22, the Building Authority may disregard any floor space that he is satisfied is constructed or intended to be used solely for parking motor vehicles, loading or unloading of motor vehicles, or for refuse storage chambers, refuse storage and material recovery chambers, material recovery chambers, refuse storage and material recovery rooms, refuse chutes, refuse hopper rooms and other types of facilities provided to facilitate the separation of refuse to the satisfaction of the Building Authority, or for access facilities for telecommunications and broadcasting services, or occupied solely by machinery or equipment for any lift, air-conditioning or heating system or any similar service. (L.N. 406 of 1987