Programming and Analysis: Net, Usable, Rentable Areas and Efficiencies

  • 10 March, 2020

When designing buildings, architects are often employed by clients who are concerned about the efficiency of space. Building efficiencies look at the ratio of net assignable space to gross area for the overall building, usable versus gross for the base efficiency, and even how large a building should be (gross square feet) in relation to the net assignable square footage versus the percentage of efficiency. What these all compare, in different ways, is the relationship of usable space to unusable or unassignable space.

Net area or net assignable space is the usable space subtracting secondary circulation. In an office, for example, this may be the area of the actual office space versus building corridors. Usable area is the net assignable area plus the secondary circulation, and the rentable area is the usable area, area for services and circulation, and excludes elevator shafts and stairs.

The reason for determining efficiencies has many benefits to the client. For example, a client may want to develop a building to rent to others (in the case of an office building). In that case, if their goal is to make the most rent from this office building, they may ask the architect to design with the least amount of circulation, which can affect the floorplate configuration for the building and its core.

A corporate office building tends to have the least efficiency and a warehouse the most. Why is that? There must be circulation and means of egress by code. If the calculation for the overall efficiency is net assignable square feet divided by the gross area, and the net assignable square feet is about half of the gross, a building with a gross square footage of 50,000 square feet would have an efficiency of 50% (overall efficiency = 25,000 ft2/50,000 ft2). Alternately, a warehouse is essentially all circulation and all net assignable square feet simultaneously. A 50,000-ft2 warehouse (using the same calculation) would produce almost 100% efficiency (or close to, it since net square footage does not account for the area of the exterior facade).

Programming and Analysis

Efficiencies can serve as a very useful tool in determining if enough space is being allocated within a building for certain programs. They can also turn the design discussion to consider space planning as well as determining the choice of mechanical system (a central system versus split/local systems or a hydronic versus air-system), structural system, envelope system, and anything that could greatly affect space. It is also important to consider that just because these are termed efficiencies, that does not always equate to better. It may actually be in the best interest of a company to have less office space and more health-based space. A healthier space (such as yoga rooms, or room for a ping-pong table) can create a more efficient staff. A company may opt for less employees but a higher level of production with such amenities. These efficiency equations cannot account for the qualitative experience of space, however, and should be used solely as a quantitative tool.

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