1. A data centre building, wherein the data centre building includes:a floor;
a plurality of rack storage areas on the floor, each rack storage area being arranged to accommodate a plurality of racks in which a plurality of rack-mountable electronic components may be housed;
one or more cold aisles, each cold aisle being adjacent to a rack storage area;
one or more hot aisles, each hot aisle being adjacent to a rack storage area;
an air cooling system comprising a non-refrigerant based cooling apparatus selected from the list consisting of a humidification unit, an evaporative cooling unit and an adiabatic cooling unit, the air cooling system also comprising a refrigerant-based cooling unit; and
a corridor separate from both the cold aisles and the hot aisles and having a height greater than 1.5 m above the floor which together with at least one of (a) the one or more cold aisles and (b) the one or more hot aisles, facilitates personnel access from outside the data centre building to the rack storage areas,
the corridor being an air supply corridor for transporting cooling air, above the floor, from the air cooling system to the one or more cold aisles.