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Thursday, December 8, 2016

Graduating from The Floor Area Ratio

The floor area ratio FAR is a zoning regulation originally created to protect public health, safety, and welfare from excessive construction in urban areas. It is a project measurement equal to gross building area divided by gross land area in square feet. A floor area ratio of 5, for instance, means that 5 acres of gross building area may be constructed on one acre of gross land area. The simplicity of the regulation is attractive, but its simplicity inadequately leads the decisions that combine to determine shelter capacity, intensity, intrusion, and dominance within projects, neighborhoods, districts, cities, and regions.  


I’ll make my point with Table 1. It is a forecast model constructed to predict shelter capacity in square feet of gross building area per buildable acre of land when no parking is required. There are eight boxes in the Land Module and five boxes in the NPL Module. The values entered in these boxes may be modified at will and represent design specification decisions. These decisions are correlated to find the maximum core area available for a building floor plan in cell G32 using the architectural algorithm in cells H3-H33. The core area found in cell G32 is used by the master equation in cell A35 to predict gross building area options in cells B40-B49. These options are based on the floor quantity alternatives entered in cells A40-A49.

The shelter capacity options related to the gross building area predictions in Col. B of the Planning Forecast Panel are calculated in cells D40-D49 using the equation in cell D39. Shelter capacity is expressed in building sq. ft. per acre.

Massing ratios related to the gross building area options in Col. B of the Planning Forecast Panel are calculated in Col. E. These ratios are used by the equation in cell F39 to calculate the intensity represented by each gross building area option in Col. B of the Planning Forecast Panel.

Related intrusion measurements are calculated in Col. G. They are used to calculate dominance options in Col. J of the Planning Forecast Panel using the equation in cell H39.

Finally, the floor area ratio representing each gross building area option in Col. B of the Planning Forecast Panel is calculated in Col. J using the equation in cell J39.

The point is that the floor area ratios calculated in Col. J of the Planning Forecast Panel react to the specification decisions entered in the 23 boxes of the NPL forecast model. The floor area ratio does not lead them, and our emphasis on the ratio as a leadership tool has produced confusion, argument, conflict, and the application of legal opinion based on the precedent of mistaken assumptions. I’ll make my point with one issue.

In my opinion, the most significant topic omitted from floor area regulation is the provision of social open space for people at street level. The opposing argument has contended that social open space is a public benefit that should be purchased at public expense. The open space specification in cell F11 of Table 1 is zero percent in cell F11 to begin an evaluation of these two positions. The value represents a developer’s attempt to maximize leasable building area on a given, high-cost urban land area. If the floor area ratio limit for Table 1 is 19, the design specification predicts that a 20 story building will produce 823,776 sq. ft. of gross building area and a floor area ratio of 18.91. I could have adjusted the specification values to make the floor area ratio exactly 19 in cell J47, but left it so I could point out that predictions will change whenever one or more specification values are modified in Table 1.

Table 2 has revised the zero percent value in cell F11 of Table 1 to 32.18%. All other specification values from Table 1 are held constant in Table 2. The 32.18 percentage has been entered to make the floor area ratio in cell J49 of Table 2 identical to that in cell J47 of Table 1. A comparison shows that the same floor area ratio and gross building area can be achieved when 32.18% of open space is provided for pedestrian relief at street level, but the trade-off is an increase from 20 stories in Table 1 to 30 stories in Table 2. The additional stories represent additional cost to reach an equal gross building area. In the past an increase in height was considered a bonus in return for social open space at the pedestrian level, but the calculations in Table 2 show that ten additional floors produce gross building area parity.

It could be argued that a bonus would involve negotiations for building height in excess of ten stories to compensate for the cost of increased building height. It could just as easily be argued that the floor area ratio of 16 was a reasonable limit; that social open space has been ignored as an essential part of the effort to protect public health, safety, and welfare within urban pattern and form; and that the deficiency should not be allowed to continue. I do not intend to resolve the argument. I only wish to point that it can be debated on a more credible foundation of measurement, evaluation, prediction, and knowledge. Cooperation between public and private interest will not be secured until all parties can sit around a table discussing options with a common language that can accurately predict implications.


In most cases a developer will know the land area involved, but in some cases he or she will be exploring the buildable land area needed to serve a given gross building area objective when a floor area ratio is given. Table 3 has been constructed to answer this question. If a floor area ratio of 16, a gross building area objective of 850,000 sq. ft. and a 30% social open space objective are given in addition to the other specification values noted, the master equation in cell A36 and the secondary equations in row 40 of the Planning Forecast Panel predict that 1.212 buildable acres will produce a floor area ratio of 16.10 in cell K49 when a 25 story building is chosen in cell A49. A slight modification to the specification values entered in the NPB Module of Table 3 could reduce 16.10 to a precise floor area ratio value of 16 in cell K49. The entire specification would represent a public/private agreement.

Table 4 shows that when no open space is provided in cell F10, the same gross building objective and floor area ratio can be reached on the same land area with only 17.5 building floors. The floors needed to compensate for the 30% public open space dedication in Table 3 would be a subject for negotiation as mentioned previously.


When social open space was introduced in Tables 2 and 3, the intensity and dominance calculations in columns F and H of the Planning Forecast Panel dropped from those calculated in Tables 1 and 4. There is no research that defines acceptable levels of intensity and dominance, but the ability to measure these conditions brings us closer to the knowledge needed to protect public welfare and improve quality of life within urban areas.

At the present time, most cities are woven together with ribbons of sidewalk and torrents of traffic. In the most extreme cases, these rivers flow between canyons of artificial stone and glass governed by skyplane regulations that attempt to ensure light, air, and ventilation penetrate to street level. In other cases, the sidewalk is omitted and replaced by a parking lot that qualifies as a front yard. In both cases, it has been our method of protecting the public health, safety, and welfare with minimum standards that are now coming into question. Why is the public being protected with government standards meant to keep them alive with a minimum quality of life (welfare)? The measurements of shelter capacity, intensity, intrusion, and dominance in Tables 1-3 represent a method of calibrating “welfare” so that research can begin to produce the knowledge needed to define minimum standards for livable cities.

The physical intensity, intrusion, and dominance of shelter, movement and life support within cities is offset by social open space. The result is referred to as urban form composition. We have yet to write the first score in this composition with a language that can lead the orchestra. The result has been discordant practice as virtuosos independently tune their instruments.

The first step is to recognize that a language is needed. The second is to recognize that cities must be woven together with social open space before they can begin to protect a population’s physical, social, psychological, environmental, and economic welfare.

Tables 1-3 were included to illustrate how open space negotiations can begin when assumptions are replaced with accurate measurement and calculation. The debate concerns the need for this open space to protect the public welfare, and the public/private share of this expense. These are political questions that require additional knowledge, and I do believe that answers are needed. The Science of City Design[1] has been written to encourage you to explore these questions with a credible language. It can lead us to a geographically limited Built Domain capable of protecting our quality and source of life -- the Natural Domain.

[1] Hosack, Walter M., The Science of City Design: Architectural Algorithms for City Planning and Design Leadership, CreateSpace, 2016. (Available in paperback and e-book versions from

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