Gross Internal Area (GIA)

Gross Internal Area (GIA) is the area of a building measured to the internal face of the perimeter walls at each floor level, which includes:

  • Areas occupied by internal walls and partitions;
  • Columns, piers chimney breasts, stairwells, lift-wells, other internal projections, vertical ducts, and the like;
  • Atria and entrance halls with clear height above, measured at base level only;
  • Internal open sided balconies, walkways, and the like;
  • Structural, raked or stepped floors are treated as a level floor measured horizontally;
  • Horizontal floors with permanent access below structural, raked or stepped floors;
  • Corridors of a permanent essential nature (eg fire corridors, smoke lobbies, etc);
  • Areas in the roof space intended for use with permanent access;
  • Mezzanine areas intended for use with permanent access;
  • Lift rooms, plant rooms, fuel stores, tank rooms which are housed in a covered structure of a permanent nature, whether or not above main roof level;
  • Service accommodation such as toilets, toilet lobbies, bathrooms, showers, changing rooms, cleaners’ rooms and the like
    Projection rooms;
  • Voids over stairwells and lift shafts on upper floors;
  • Loading bays;
  • Areas with a headroom of less than 1.5m;
  • Pavement vaults;
  • Garages; and
  • Conservatories.

The GIA excludes:

  • Perimeter wall thickness and external projections;
  • External open-sided balconies, covered ways and fire escapes;
  • Canopies;
  • Voids over or under structural, raked or stepped floors;
  • Greenhouses, garden stores, fuel stores and the like in residential property; and
  • Open ground floors and the like.

To meet international standards, a slightly different definition can sometimes be applied to offices.  However, in this context we are primarily interested with the GIA of the actual building.

Source: RICS

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