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Used when calculating Business Rates Gross Internal Area (GIA) measures the overall size of a location to help determine it’s rateable value. This is the area of a building measured to the internal face of the external 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
  • atria and entrance halls with clear height above, measured at base level only
  • internal open sided balconies, walkways
  • 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 (such as fire corridors, smoke lobbies)
  • 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 above main roof level or not
  • service accommodation such as toilets, toilet lobbies, bathrooms, showers, changing rooms, cleaners rooms
  • 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
  • conservatories

It 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
  • open ground floors

The GROSS internal area (NIA) is used as part of the Business Rates Measuring Method

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