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