Last edited 17 Sep 2018

Net internal area NIA

The area of a building can be measured in a number of different ways:

It is very important when describing the area of a building to be clear about which measure is being used, for example in property sales, planning applications, building regulations applications, lease negotiations, rating valuations, and so on.

The net internal area (NIA) of a building is the usable area measured to the internal finish of the perimeter or party walls, ignoring skirting boards, at each floor level. Net internal area covers all of those areas that can be used for a particular purpose.

The UK government’s Valuation Office Agency (VOA) Code of measuring practice: definitions for rating purposes suggests that Net Internal Area includes:

Net internal area excludes:

It suggests that, 'essential access' '...will not include reception areas or areas capable of use and situated within entrance halls, atria and landings etc.'

In relation to the term 'permanent essential nature' it suggests that, 'apart from areas used in common with other occupiers, corridors excluded from NIA are those of a permanent essential nature, i.e. internal corridors between structural walls (usually found in older buildings). Fire corridors and smoke lobbies which are defined by non-structural walls - but only where they are permanent and essential to any prospective tenant of the property and do not merely serve the needs of the actual occupier. If the latter, they should be included.'

RICS Guidance Note, A guide for Property Professionals, 6th Edition Code of measuring practice 2007, is in general agreement with the Valuation Office Agency definition, of net internal area.

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