Which option correctly represents the ratio used to measure building efficiency as net usable space divided by gross space?

• A. Net rentable space to gross space
• B. Gross space to net usable space
• C. Net usable space to gross space
• D. Occupied space to total space

Answer: (C)

Building efficiency is assessed by the proportion of space that occupants can actually use to work relative to the total floor area. Net usable space represents the areas available for occupant activities (offices, desks, meeting rooms, etc.), while gross space includes everything on the floor — walls, mechanical rooms, corridors, lobbies, restrooms, elevators, and other non-usable or shared areas. Therefore, the ratio that expresses efficiency is net usable space divided by gross space. This yields the fraction of the floor that can be actively utilized. The other concepts mix different terms (such as rentable area or occupancy) or invert the relationship, which is why they don’t correctly describe this efficiency metric.