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Wednesday, January 25, 2012

Parking Variances Offer a Glimpse into the Future

Parking variance requests indicate the need for more informed development capacity evaluation and design regulation. The improved platform is needed to provide leadership for more consistent and sustainable design excellence throughout a limited Built Domain.  

If an owner knows that he wants to construct a 30,000 sq ft. building with a parking lot and a parking requirement of one space for every 250 sq. ft. of gross building area (a250), the Planning Forecast Panel in Table 1 predicts rows of options related to the building height alternatives (f) listed in its left hand column.1 If we look across from the 3 floor option, the buildable acres column (BAC) in Table 1 tells us that he would need 1.987 acres based on the values entered in the Design Specification Template above. For the sake of this example, he owns 1.5 buildable acres and a quick scan down the BAC column tells us that even a 15 story building would require 1.713 acres. Obviously, some design adjustments are needed. Unfortunately, the (s), (a) and (S) values in the Design Specification Template, and the (f3) value in the Planning Forecast Panel, represent zoning ordinance requirements for this example; and at least one variance is needed to reduce the BAC required.

The arrows in Table 1 point to zoning requirements that will be discussed as variance options. Decisions lead to variance requests that are evaluated by a public Board of Zoning Appeal. Unfortunately, its decisions can be arbitrary because the logic for these regulations is poorly documented. This makes the regulation suspect and decision a matter of opinion among appointed residents. It’s no wonder we have sprawl, but let me finish this example by discussing the variance options in play before commenting further.

Table 1: Buildable Acre Requirements Based on a Given Gross Building Area Objective and a Template of Design Specification Values

Option 1: If the owner tested a parking variance from a250 to a355 in Table 1 while all other values remained constant, the BAC column in the Planning Forecast Panel would forecast the land area needed as 1.501 acres for a 3 story building.

Option 2: If the owner tested a project open space variance from 30% to 8.3% (S.3 to S.083) in Table 1 while all other values remained constant, the BAC column in Table 1 would again forecast the land area needed as 1.501 acres for a 3 story building.

Option 3: If the owner tested a reduction in the parking lot area provided per space from 400 sq. ft. per space (s400) to s282, the BAC column in Table 1 would forecast the land area needed as 1.502 acres for a 3 story building.


There are very practical problems with each of the variance options mentioned.

Option 1: Requesting a parking variance reduces the number of spaces provided, but the owner will argue that this is all that is needed in his particular case. This tailors the building to his need and ignores future owners. The city’s economic interest, however, depends on the building as a continuing source of public revenue that must maintains its attraction to future buyers.

Option 2: Most zoning ordinances don’t specify open space beyond setback requirements, and these can often be paved under the concept that a parking lot is open space. This is unfortunate because storm sewer sizes depend on runoff assumptions that depend on the relationship between open space and impervious development cover. A city that does not know these storm sewer runoff assumptions can easily permit excessive building cover and pavement that exceeds a property owner's share of capacity. In this theoretical example, a reduction to 8.3% open space might not even be feasible if the land has an irregular shape or other unusual characteristics that cannot accommodate the building and parking cover needed.

Option 3: An average surface parking lot area of 282 sq. ft. per space is not feasible when circulation aisles and turning islands are included in the calculation.


Option 3 is not realistic. Option 2, if possible, represents a building sitting in a parking lot. This is a solution that is familiar to all of us, but is vulnerable to decline, a threat to storm sewer capacity and a negative influence on neighborhood context and appearance.

Option 1 sacrifices public benefit for private gain. The parking lot may indeed be adequate for the owner’s purpose, but the building he occupies must continue to be useful after he leaves. If it is handicapped by inadequate parking, the community may suffer from a decline in attraction that can affect its economic stability over time.

A city is in the business of averages that protect its stability. Special exceptions defeat this purpose, and parking variances are a common attempt to over-develop land with exceptions that can easily threaten future value. The argument is often based on a claim of “hardship”, but the only hardship in this example is inadequate land area to accomplish the development objective. The claim that the parking requirement itself is a hardship based on the characteristics of a specific activity is a typical argument. It’s often successful because the requirement depends more on precedent than documented analysis. This leads to the claim that it is excessively restrictive in specific cases, but the law is written to protect the future with average values -- and the debate continues to search for proof that will always be an approximation.

Option 1 has just shown that the land owner must exceed the parking limit of a250 by 29.6% to reach his development capacity objective of 30,000 gross sq. ft. with a 3 story building. If a Board of Zoning and Planning approved this request, it would be similar to approving an 84.2 mile per hour speed in a 65 mile per hour zone, and most of us know there are limits to the latitude that should be taken.


The previous options have been based on data forecast from software model CG1B in the DCE software collection. Option 4 is based on forecast model CG1L and predicts the realistic gross building area capacity of the 1.5 acre land area just discussed. By locating the intersection of (f3) with the GBA column, you can see that the site has 23,658 gross sq. ft of building capacity when 3 floors are considered and 30% open space is specified. This increases to 24,723 sq. ft. if a 1 story height variance is granted to the (f4) row; and to 25,410 gross sq. ft. if a 2 story height variance is granted to the (f5) row, assuming all other zoning requirements are met. Neither variance comes close to the 30,000 sq. ft. objective.

If city storm sewer capacity in this area was originally designed for runoff from 30% impervious cover, 70% open space was anticipated. In this case, Option 4 would predict that 3 story gross building area capacity would decline to 10,139 sq. ft.

Option 4: The Realistic GBA Capacity of 1.5 Buildable Acres

Chart 1 has been created to plot the relationships just mentioned. Buildable area from 1 to 7 acres is arranged along the y-axis. Project open space options from 8.3% to 70% are arranged along the x-axis. Each line in the chart represents a building height option from 1 to 5 floors. All lines show that buildable acre predictions increase when unpaved project open space (S) increases along the x-axis and the gross building area objective remains constant at 30,000 sq. ft.. At any open space increment, a vertical line would intersect with all building height options and reveal the buildable acres required for each option. The results confirm what you would intuitively expect, but with mathematical accuracy.

Chart 1: The Effect of Building Height and Project Open Space Combinations on the Buildable Land Area Required


The relationship of building height to building cover produces building mass more commonly known as cubic area. Parking, loading and miscellaneous pavement combine with building cover to produce development cover, or impervious cover in civil engineering terms. The amount of gross building area that can be constructed per buildable acre is development capacity. The amount of open space provided on the same buildable area restricts development capacity by introducing context. The relationship of capacity to context is intensity. Intensity (INT) can be classified in the simplest terms by noting the number of building floors and percentage of total development cover planned or provided.

More specifically, intensity is the gross building area constructed in sq. ft. (GBA) per buildable acre involved (BAC), and is limited by the open space area introduced. The result is capacity and context. The capacity defined by design specification values shelters activity. The types and quantities of activity attracted determine economic stability.

Capacity can be measured on an intensity scale. A complete scale is represented by the design specification template in a forecast model. These values can be measured at existing locations. Other values can also be tested in a design specification template to forecast context, capacity and intensity options. This process of measurement, evaluation, decision and direction is an approach that can contribute to integrated open space and sustainable city design.

The lack of an adequate intensity measurement and forecasting system has obstructed our pursuit of knowledge. The obstruction has been removed with the DCE forecasting system. Its use can help us pursue knowledge that will determine our success in providing shelter for growing populations within a limited Built Domain that does not threaten its source of life – The Natural Domain.


A parking requirement is part of an intricate web of design specification values that combine to determine the context, capacity and intensity of an intended activity. When a design specification value represents a zoning requirement, its impact can be easily forecast with the DCE collection of forecast models. At this point it is an essential tool because we have limited confidence in specific zoning requirements. The result has been guesswork, a lack of public conviction, and doubt that leads to arbitrary variances, excessive intensity and sprawl.

The problem begins with the tools. City planning has had difficulty dealing with three dimensions, but cities are not only compromised by two-dimensional land use conflicts that require separation. They also suffer from an inadequate ability to forecast the consequences and opportunities of context, capacity and intensity options.  

The pressure of expanding populations and economic instability can easily lead us to sacrifice context for intensity. This increases shelter capacity and economic yield per acre, but it comes at the cost of context. We intuitively know that excessive intensity can threaten our quality of life, not to mention our sustainable future; but we haven’t been able to measure and evaluate the options. This has left use with sprawl while contemplating variance requests without an adequate frame of reference.  

In the end, our ability to evaluate variance requests will reveal the progress we have made toward a limited Built Domain that does not threaten its source, or quality, of life.

1Data predicted by forecast model CG1B in a software collection entitled Development Capacity Evaluation v.2. The collection is attached to its manual of explanation, Land Development Calculations, ed.2. The book and software have been written by Walter M. Hosack and published by the McGraw-Hill Companies, 2010.

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