Floor plate efficiency is the ratio of usable square footage to rentable square footage on a given floor of an office building, expressed as a percentage. Under BOMA/ANSI Z65.1, the measurement standard adopted by virtually every institutional landlord and appraisal firm in North America, rentable area includes each tenant's usable area plus a proportional allocation of common areas such as lobbies, corridors, restrooms, and mechanical rooms.
The difference between rentable and usable area is captured in the core factor (sometimes called the loss factor or load factor), which represents the percentage of rentable area that the tenant pays for but cannot physically occupy. A building with a 15% core factor delivers 85 cents of usable space for every dollar of rent paid on a per-square-foot basis.
Efficiency varies significantly based on building design. Central-core towers, where elevators, stairs, and mechanical shafts are grouped in the centre of the floor plate, typically deliver efficiencies between 80% and 88%, depending on the number of elevator banks and the depth of the structural core.
Side-core or split-core designs can push efficiency above 90% by moving services to one edge and freeing up contiguous usable space, but they are more expensive to construct and less common in high-rise development. Column spacing, curtain wall mullion depth, and perimeter HVAC unit enclosures all consume usable area and reduce the efficiency a tenant actually experiences.
For tenants, floor plate efficiency directly determines the effective cost of occupancy. A tenant quoted $50 per rentable square foot in a building with an 82% efficiency is paying approximately $61 per usable square foot, the space the tenant can actually furnish and occupy.
The same quoted rent in a building with a 90% efficiency translates to approximately $56 per usable square foot. Sophisticated tenant representatives convert every lease proposal to a per-usable-square-foot basis before comparing competing options, because the quoted rentable rate alone can be misleading when buildings have materially different core factors.
Institutional investors analyse floor plate efficiency when underwriting office acquisitions because it affects both tenant demand and replacement risk. Buildings with poor efficiency face structural competitive disadvantage: tenants comparing options on a usable-square-foot basis will favour more efficient buildings at comparable quoted rents, and landlords in inefficient buildings must either discount rent or accept longer vacancy periods.
In markets with rising construction standards, older buildings with low efficiency ratios may face functional obsolescence that no capital program can cure, a factor that appraisers capture as an incurable depreciation deduction under the cost approach.
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