Measurement examples

NIA is the usable area within a building measured to the internal face of the perimeter walls at each floor level:

Included

• atria with clear height above, measured at base level only;
• entrance halls;
• notional lift lobbies and notional fire corridors;
• kitchens;
• built-in units, cupboards and the like occupying usable areas;
• ramps, sloping areas and steps within usable areas;
• areas occupied by ventilation/heating grilles;
• areas occupied by skirting and perimeter walls;
• areas occupied by non-structural walls;
• subdividing accommodation in sole occupancy; and
• pavement vaults.

Excluded

• those parts of entrance halls, atria landings and balconies used in common;
• toilets, toilet lobbies, bathrooms and cleaners’ rooms;
• lift rooms, plant rooms, tank rooms (other than those of a trade process nature) and fuel store;
• stairwells, lift-wells and permanent lift lobbies;
• corridors and other circulation areas where used in common with other occupiers;
• permanent circulation areas, corridors and threshold/recesses associated with access, but not those parts that are usable areas;
• areas under the control of service or other external authorities including meter cupboards and statutory service supply points;
• internal structural walls, trunking enclosing excluded areas, columns, piers, chimney breasts, other projections, vertical ducts and walls separating tenancies;
• the space occupied by permanent and continuous air-conditioning, heating or cooling apparatus and ducting in so far as the space it occupies is rendered substantially unusable;
• the space occupied by permanent, intermittent air-conditioning, heating or cooling apparatus protruding 0.25m or more into the usable area;
• areas with headroom of less than 1.5m;
• areas rendered substantially unusable by virtue of having a dimension between opposite faces of less than 0.25m; and
• vehicle parking areas (the number and type of spaces noted).

Figure 4 Net internal area