net area

In architecture, construction, and real estate, floor area, floor space, or floorspace is the area (measured in square metres or square feet) taken up by a building or part of it. The ways of defining "floor area" depend on what factors of the building should or should not be included, such as external walls, internal walls, corridors, lift shafts, stairs, etc. Generally there are three major differences in measuring floor area.

Gross floor area (GFA) - The total floor area contained within the building measured to the external face of the external walls.
Gross internal area (GIA) - The floor area contained within the building measured to the internal face of the external walls.
Net internal area (NIA) (or Net floor area NFA, or Usable floor area UFA) - The NIA is the GIA less the floor areas taken up by lobbies, enclosed machinery rooms on the roof, stairs and escalators, mechanical and electrical services, lifts, columns, toilet areas (other than in domestic property), ducts, and risers.

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