Net Internal Area

Net Internal Area

For Business Rate purposes the net internal area (NIA) is the total usable area of each floor within a building, measured to the inside face of the boundary walls (ignoring skirting boards). Areas measured include:

• kitchens
• any built-in cupboards or units that occupy usable areas
• perimeter skirting boards, mouldings and trunking
• open circulation areas such as atria, corridors and entrance halls
• Partition walls and other dividing elements

Areas that are excluded are:

• internal structural walls
• walls (whether structural or not) enclosing excluded areas
• piers, columns, chimney breasts, ducts and other projections
• cleaner cupboards
• lifts, lift rooms, lift wells
• stairwells and landings
• stairwells, entrance halls, atria, landings and balconies used in common or for essential access
• corridors and other circulation areas used in common with other occupiers or of a permanent essential nature
• boiler rooms, fuel stores, plant rooms and tank rooms other than those of a trade process nature
• car parking areas
• spaces occupied by cooling and heating equipment, air conditioning systems and ducting which renders the space substantially unusable
• areas with a headroom of less than 1.5m
• toilets and associated lobbies, unless additional toilets have been installed
• areas under the control of service or other external authorities

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