Net Internal Area (NIA) is the method of measurement used for the valuation of commercial property, such as retail, office space, warehouse space, etc.
The NIA is defined as the usable area that is encompassed by the internal footprint of the perimeter walls of a property.
According to RICS the measurement of the Net Internal Floor Area should include entrance halls that are not used in common with other tenants of the building, ramps and stairs, kitchens, cupboards and other build-in units that occupy usable areas, and pavement walls but should exclude areas that are used in common by the tenants of the property such as entrance halls, lifts, stairwells and other common areas, meter cupboards, areas with headroom below 1.5 meters, etc.
The Net Internal Area represents an important factor in estimating the value of a property, as it is typically multiplied with the appraised value per square meter for the particular property and location. In this way, it is crucial in determining the final estimate of the value of the property.