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Saturday, October 22, 2016

The Density Distraction in City Planning

Density is a social statistic. It cannot lead the formation of shelter for human activity within urban areas. It has caused confusion, contradiction, disagreement, and conflict within and between those in the public and private sectors; but it is now possible to replace the statistic with a language that can accurately measure the past, evaluate the present, predict the future, and define decisions in terms that have the accuracy needed for leadership direction. In order to make my point, I need to introduce the language, illustrate its leadership potential, and compare it to the performance of density statistics.


Gross building area is a fully enclosed square foot area that can be occupied by any activity. Shelter capacity is the gross building area that can be constructed per buildable acre available, and there are many options. The amount of gross building area provided per acre, in addition to the supporting pavement introduced, is referred to as a level of “intensity”. Intensity is moderated by the amount of unpaved project open space that remains. At one end of the spectrum is a small building on thousands of ranch acres. At the other is a high-rise building on a fraction of an acre. In both cases, the square feet of shelter and pavement constructed consume land that is a natural source of life.

Activity is referred to as “land use”. The relationship of shelter capacity and activity to geographic location affects economic stability and public acceptance. In other words, shelter capacity, condition, and location produce levels of physical intensity, social activity, and economic contribution that affect our quality of life within any urban area.

The Movement, Open Space, and Life Support Divisions of our Built Domain consume natural land to serve a Shelter Division that adds to the consumption and is sprawling without restraint. The square feet of building area and pavement introduced per acre determines the population and activity that can be served, as well as the physical intensity introduced. The social open space that remains contributes to the external quality of life provided. In other words, the physical, social, and economic characteristics of intensity not only affect the health, safety, and welfare of a population within The Built Domain; but the survival of its source of life beyond. We must begin to understand these relationships.

Six building design categories encompass most of the shelter provided on the planet. They are:

1)      G1: Buildings with surface parking around, but not under the building
2)      G2: Buildings with surface parking around and/or under the building
3)      S1: Buildings with structure parking adjacent to the building on the same parcel
4)      S2: Buildings with underground parking
5)      S3: Buildings with structure parking at grade under the building
6)      NP: Buildings with no parking required

The parking structure options may have supplemental surface parking, but when a parking garage is present, the building is classified by the garage configuration present. These building categories may be occupied by any activity group that complies with local building and zoning requirements.

The point is that shelter classification begins with the building design category involved, and each category has gross building area limitations defined by design specification decisions. These decisions limit the scope of land use activity and revenue potential that can be introduced.


Table 1 presents a set of optional decisions for the G1 Design Category. They are represented by the specification values entered in the boxes of its Land and G1 Modules. There are fifteen specification boxes and each value represents a design decision that can be adjusted to explore shelter capacity alternatives. The equations in Col. H of Table 1 convert specification decisions to implications in Col. G. The objective of the algorithm is to distill the core buildable land area available in cell F32.

The master equation in cell A37 correlates the core area found in cell F32 with the parking decisions entered in cells F33 and F34 and the floor quantity options entered in cells A42-A51. It predicts gross building area alternatives in cells B42-B51 based on these floor quantity options. The remainder of the Planning Forecast Panel predicts additional implications related to the gross building area options in Col. B using the secondary equations on line 41. Shelter capacity options corresponding to the gross building area options forecast in Col. B are listed in Col. F. The entire panel illustrates a few of the many implications that can be forecast as a function of gross building area predictions. Revenue, expense, construction cost, return on investment, population, and traffic generation are a few that are not shown.

Table 1 illustrates the many specification decisions required to calculate shelter options for the G1 Design Category. A change to one or more values entered in the boxes of Table 1 would produce a new forecast in Col. B of the Planning Forecast Panel, and hundreds of options could be predicted in less time than it would take to produce one sketch.

The unpaved open space percentage specification in cell F11 of Table 1, and the impervious cover limit calculated in cell F12, represents one of the decision / implication relationships that play a significant role in the calculation of shelter capacity options. An unpaved open space decision, however, is only one of many design decisions that combine to determine shelter capacity options.

Open Space

It’s easy to overlook open space because its value to our quality of life is currently a function of subjective opinion, and this opinion can reduce private return on investment. It is an inevitable conflict, but one open space decision has already been made that is unrecognized by most.

Unpaved open space protects storm sewer capacity from excessive runoff. Storm water runoff is produced by impervious cover and re-directed by storm sewer capacity. Capacity is expressed as the percentage of impervious cover that can be accommodated by a given pipe size. Subtracting this percentage from 100 yields the amount of unpaved open space expected, unless more intricate civil engineering solutions are introduced. A greater pipe size can accommodate a greater percentage of impervious cover, but the pipe cost increases as well. A developer often attempts to minimize cost by minimizing pipe size. This reduces the impervious cover percentage that can be accommodated, but the limit is often over-looked by decision-makers for any number of reasons. If an impervious cover limit is exceeded by many along a branch storm sewer line, unpaved open space declines and flooding is an inevitable consequence, unless detention solutions are introduced. Flooding can easily occur when a community does not know the impervious cover capacity of each branch line in its storm sewer system and approves building and pavement additions over years based on the assumption that growth is good. Unfortunately, the unpaved open space percentage required to protect storm sewer capacity may not be adequate to protect the neighborhood’s quality of life.

Shelter Capacity and Intensity

The gross building area options forecast in Col. B of the Planning Forecast Panel of Table 1 were used to produce the shelter capacity options in Col. F and the intensity options in Col. G. These intensity levels are like the first blood pressure readings. I can only hope that continued measurement and evaluation will produce intensity knowledge and parameters that can lead to an improved quality of life.

Intensity options are produced by values entered in a design category specification template. A leadership decision is taken by defining the design category and specification values adopted for a given location.

Design category choices and specification decisions have gross building area implications. Gross building area divided by buildable land area is shelter capacity. The ability to accurately define gross building area options with a design category master equation makes it possible to predict many implications that are functions of the square foot options predicted.

Urban Form

Building arrangements are often referred to as massing compositions. A collection of compositions is referred to as urban form. Ideally, a plan for urban form allocates the Shelter, Movement, Open Space, and Life Support Divisions of The Built Domain to serve growing populations within geographic limits that protect their quality and source of life – The Natural Domain.

Master equations make it possible to measure, evaluate, diagnose, and prescribe urban form one project at a time. When a Built Domain is geographically limited, the quality of life within these limits will be a function of the design categories and specification values chosen to create urban form. Our quality of life is affected because we must live within and among the buildings, pavement, spaces, and movement systems we create.

Several Shelter Design Principles

Table 1 is based on 40% unpaved open space in the buildable land area. When the gross building area values in Col. B of the Table 1 Planning Forecast Panel are mapped in Figure 1, the results can be expressed in the following terms:

The rate of increase in gross building area declines at an accelerating rate as the number of building floors increase in the G1 Design Category.

Building cover declines more rapidly than gross building area increases because the gross building area permitted per parking space (a) in Table 1 is less than the parking lot surface area planned per parking space (s).

Figure 1 illustrates the dramatically decreasing rate of increase in gross building area as building height increases. Gross building area increases from 38,577 sq. ft. to 59,000 sq. ft., but it barely increases above the five story mark of 55,722 sq. ft. This occurs because gross building area does not increase as rapidly as surface parking area when (a) is less than (s). Expanding parking area for additional spaces is required to justify increased building area, but this eventually reduces the land remaining for building cover to unrealistic levels.

Figure 2 is based on (a) being greater than (s) and 15% unpaved open space being entered in Table 1. Figure 2 shows that gross building area still increases at a decreasing rate, but the results produced are dramatically different because of the specification value changes. Gross building area increases from 85,630 sq. ft. to 186,152 square feet, but gross building area slowly increases above the 5 story mark of 164,673 sq. ft. Parking cover consumes the same amount of land per space, but gross building area per parking space grows more than parking lot area per space. This scenario explains why the gross building area arc increases more rapidly than the building cover arc declines in Figure 2.

When the five story gross building area potential in Tables 1 and 2 is subtracted from the one story gross building area potential predicted, the results expose another design principle. In the case of Figure 1, the total gain for 1-5 stories is 17,145 sq. ft. The total gain for 5-10 stories is 3,278 sq. ft. In the case of Figure 2, the total gain for 1-5 stories is 79,043 sq. ft. The total gain for 5-10 stories is 21,749 sq. ft. This observation produces the following principle.

The most rapid increase in G1 gross building area occurs within a 1-5 story range.

The actual gain from 1-5 stories is a function of all design specification decisions entered in Table 1. Above 5 stories, the gross building area gain per additional floor becomes increasingly less cost-effective.

Figure 2 produces much greater gross building area potential, but is the open space and parking reduction desirable? I won’t attempt to answer the question. I’m simply pointing out an issue that can be accurately measured and evaluated with comparative studies using the language of City Design. In fact, the complete language of City Design can be used to measure existing conditions, evaluate future potential, and accurately define leadership decisions with confidence based on objective measurement and comparative evaluation.

Figures 1 and 2 explain why the gross building area permitted per parking space (a) and the unpaved open space percentage proposed per project (OSAU) are two of the most common points of public and private disagreement. Greater open space and parking requirements reduce potential gross building area and private return on investment, but at what point do the reductions produce excessive intensity in the neighborhood? This cannot be answered without a comprehensive method of measuring and evaluating existing conditions. It cannot be improved without an accurate method of converting measurement and evaluation to accurate, comprehensive, and correlated leadership expression. A new language of city design is needed. I’ll get to this in the final section of this essay.

The G1 design principle behind this section of the essay can be stated in a single sentence.

Every additional surface parking space justifies increased gross building area; but reduces the core land area available for building cover, until the core area remaining becomes too small to accommodate a realistic floor plan.

Figures 1 and 2 demonstrate that planning and design issues can be expressed in mathematical terms. This has the power to persuade in a political environment of conflicting opinion. It also improves our ability to collaborate with the science of others; since the land our planet can donate to shelter, and the shelter capacity of this land, is becoming an issue of survival. The answers we find will be reflected by the context, composition, and function of urban form. The appearance of these solutions will symbolize our progress toward the symbiotic correlation of Shelter, Movement, Open Space, and Life Support within a geographically limited Built Domain that protects our quality and source of life – The Natural Domain.


Density is a statistic that indicates the number of residential dwelling units provided or permitted per acre of land occupied. The gross building area potential of the land given the combined effect of all zoning regulations is ignored because accurate calculation has been elusive, but feasibility is a function of the relationship between dwelling unit quantity, unit area, and gross building area potential. A density statistic cannot provide the correlation required for adequate leadership.

Table 1 has illustrated the correlated design specification items, topics, and master equation that produce gross building area options per buildable acre for the G1 Design Category. A feasible density is one that multiplies dwelling unit area by quantity to fit within the gross building area potential of a given land area. Density does not lead to the gross building area potential of land. It is limited by the specification decisions that determine gross building area, and unachievable density regulations or goals simply introduce confusion and frustration.

Density is oblivious to the inter-active design specification decisions in Table 1, but they determine gross building area potential and intensity implications for any given land area. It is also oblivious to the various dwelling unit area decisions that can increase or decrease density within gross building area potential. The conflict between ambiguous density regulation, uncorrelated zoning regulation, and the gross building area potential of land is often inevitable.


The creation of urban form begins with an ability to predict gross building area capacity, intensity, and activity options for every land area and location within the geographic area defined.

Our current inability to correlate the realistic gross building area potential of land with the activity permitted and quality of life desired produces confusion, conflict, and suspicion that can only be resolved with opinion and compromise. This often produces arbitrary decisions and unsatisfactory results that assemble over time.

The gross building area options produced by correlating the design specification decisions in Table 1 could not have been produced by an independent density statistic. The observations produced by charting the Table 1 options in Figures 1 and 2 would remain unknown or intuitive at best. There are just too may design decisions involved that affect and precede density calculation and can’t be led by a density statistic. It is not a credible minimum design standard capable of consistently leading shelter capacity toward urban form capable of increasing capacity and improving our quality of life. It is a rear view mirror, not a heads-up display of options and opportunities.

I have written The Science of City Design to explain design categories, activity groups, design specifications, architectural algorithms, master equations, and planning forecast panels. These topics introduce a vocabulary and language of city design that can consistently improve planning results by correlating the decisions required to shelter growing populations within a limited Built Domain. The goal is to protect this population’s quality and source of life.

For those interested in pursuing the study of city design, urban form, and its physical, social, psychological, environmental, ecologic, and economic implications; The Science of City Design can be found at in e-book and paperback versions.

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