DENSITY
Density is the number of dwelling units planned, permitted
or present per acre. It is an attempt to measure the compression produced by
the proximity of adjacent dwelling units. It is an ambiguous unit of
measurement, however, that ignores the total impervious cover introduced per
unit and the buildable land area available within the acre. In other words, the
percentage of building cover and other impervious cover planned is ignored. Ignoring
impervious cover can increase the intensity produced by the permitted density. Ignoring
unbuildable areas such as rights-of-way, wetlands, and ravines within the acre reduces
density when included but increases intensity among the units placed on the
remaining buildable land area.
To begin with, density only applies to residential
land use activity. Its leadership potential is compromised because it is not
comparable across all land use activity groups. It is not even comparable
among residential activity groups because of inconsistent and incomplete
measurement standards. This has frustrated universal measurement, comparison, evaluation,
correlation, and formation of shelter capacity, intensity, and context
knowledge that can improve leadership potential.
INTENSITY
I have used the word “compression” because it is commonly
understood to mean opposing forces producing degrees of pressure. I prefer the
word “intensity” for urban design because it more accurately implies the
pressure imposed on pedestrians in space by adjacent static and moving objects
like building mass, parking, pavement, and traffic volume. Claustrophobia in an
alley is an extreme example of three-dimensional spatial compression and
intensity perceived at one end of a physical intensity spectrum that can be
mathematically calculated.
Project intensity is relieved by the amount of passive,
unpaved open space introduced but it may not be a straight-line relationship
with building mass. Traffic volumes increase intensity but have not been
included in the forecast models that will be presented because the focus is on
project context.
The forecast models to be presented predict gross building
area alternatives that produce shelter capacity, intensity, intrusion, and
context options for project locations that have social and economic
implications. When traffic volumes and adjacent projects are considered, the
issue expands to become one of urban design evaluation.
Density may be convenient shorthand, but it is not equal to a
leadership challenge that requires mathematical measurement, prediction,
evaluation, information management, and data science at the very least to
provide the leadership guidance needed for the many decisions that require
correlation.
DENSITY CALCULATION
Tables 1-2 are examples of density guesswork based on a
townhouse building configuration. They will make the point that a permitted
density establishes a limit that may conflict with other independent
regulations and cannot correlate the 64 specification topics and decisions that
guide townhouse design toward an objective.
Tables 1 and 2 illustrate the 64 specification topics and
decisions that guide townhouse site planning.
TABLE 1
Table 1 pertains to the G1 Building Design Category when
occupied by R2 townhouse activity. The G1.R2
Activity Group includes attached, independent dwelling units served by grade
level parking and/or garages and carports. The group is distinguished by the
unique shaded specification topics in the Table 1 forecast model.
An architect, landscape architect, civil engineer, site planner, and so on often knows the applicable land area, zoning, and density limitation for a client. This gives the client an expectation of the dwelling unit quantity they can build on their land when they multiply their total acreage by the number of dwelling units permitted per acre. This can lead to exaggerated expectations when applied to a specific land area. For instance, Table 1 shows that 20 acres are owned by a developer in cell F3 and a density of 12 dwelling units per acre is permitted in cell F23. This would lead to a 240-dwelling unit expectation.
Land Module
Some land cannot be used as a shelter location, so the first
challenge in Table 1 is to define the available shelter area in cell F17 for
the 20 acres given in cell F3. Buildable Land Area is calculated in cell F10.
Unpaved Open Space is specified in cell F11. In this case, the 40% open space entered
can be considered either discretionary or required by the local zoning
ordinance. This means that storm sewer capacity must be able to serve the 60%
impervious cover that will remain. Shared, or common, unpaved and paved open
space is specified in cells F13 and F14 for the buildable land area calculated
in cell F10. The Shelter Land Area remaining for improvement is
calculated in cell F17 by subtracting the shared open space values entered in
cells F13 and F14. This is the land available for further improvement, and the
land on which achievable dwelling unit quantity will be calculated.
Limitations Module
At this point, the site plan designer knows the permitted density
entered in cell F23 of Table 1 and can calculate the number of dwelling
units permitted on the remaining shelter area in cell F25. The remaining calculated
data in the module expands the scope of information related to the density requirement.
Building and Pavement Module
The specification data entered in cells F30-F34 is estimated
by the designer. The specification value decisions entered in the remaining 55
shaded cells of this module represent the townhouse design specification
decisions desired by the client. The values calculated on line 43 of the module
are averages derived from the shaded specification value decisions entered
above.
Planning Forecast Panel
The values calculated on lines 54-58 of the panel are based
on the equations of line 53. The average for each column is calculated on line
59. The most significant values in the panel include the average land area per
dwelling calculated in cell J59, the density that would be produced by the
total specification in cell J61, and the number of dwelling units produced by
the specification in cell K59.
Implications Module
This module provides an evaluation of the 64 shaded cell
specifications entered. Cell J61 shows that the design specifications will
produce a density of 13.47 dwelling units per shelter acre instead of the 12 permitted
in cell D64. Cell E66 notes that this is not feasible given the density
limit. Cell D68 shows that the specifications will produce 220.99 dwelling
units instead of the 196.8 limit shown in cell D67. Cell D70 calculates that
the specifications will produce an average land area per dwelling unit of 3,233
square feet per unit instead of the density limit of 3,630 square feet shown in
cell D69.
The site plan based on the client specification in the
Building and Pavement Module would require a variance since cell K59 shows that
221 dwelling units would be provided by the instead of the 196.8 calculated in
cell F25.
Adjustment Alternatives
The first remedy would be to increase the unpaved
open space percentage entered in cell F11 if not mandated by the zoning
ordinance. This would reduce the shelter area available for dwelling quantity
and reduce the density calculated. The second would be to alter the
dwelling unit mix or increase the dwelling unit areas entered in cells B38-C42
to reduce the number of dwelling units calculated in cell K59. The third
option would be to increase the amount of parking to reduce the shelter area
available for dwelling unit quantity. The fourth would be to reduce the
floor quantities assigned to each dwelling unit type in cells D40-D42 to increase
the land area consumed by each dwelling unit and reduce the quantity provided.
The fifth option would be any combination of the preceding four. These
options illustrate the time-consuming guessing game that would occur at the
drawing board without this forecast model evaluation.
TABLE 2 ADJUSTMENT
Table 2 adopts the first remedy for design revision to reach
the density permitted. It is the easiest to accomplish and involves simply increasing
the unpaved open space percentage in cell F11 from 40% to 47%. This reduces the
achievable number of dwelling units to195.2 instead of the 240 expected when
first reading the zoning ordinance.
Getting to this point involves guesswork without a forecast model
and can stimulate variance requests given the time required to revise the
design example presented in Table 1. If there are no open
space requirements and no reduction of gross land area to find buildable land
area, the road to 240 dwelling units is a potential path to excessive intensity. This example implies the adjustments that would be required.
TABLE 1 AND 2 SUMMARY
Reading the different shelter capacity, intensity, and
context measurements in Tables 1 and 2 are like reading blood pressure without
a history of its implications. The Table 1 Implications Module measurements were
density=13.47 dwelling units per shelter acre; shelter capacity=18,776 sq. ft.
per shelter acre; intensity =0.259; and context=0.597. The Table 2 measurements
were density=11.90 dwelling units per shelter acre; capacity=16,585 sq. ft. per
shelter acre; intensity =0.202, and context=0.540. At this point in the history
of urban design and city planning there is no measurement, research,
evaluation, and accumulated knowledge that can indicate the positive or
negative results that will be produced by these measurements.
CONCLUSION
The purpose of this exercise is not to pass judgment. It is
to show that a density regulation leaves too much to chance when many (in this
case 64) design topics are involved. This is equal to 1.26887E+89 or 1.26887 x
1089 potential topic decisions. The
choices required to meet a density limit cannot help but involve guesswork and
conflict when mathematical shelter capacity evaluation and guidance are not
involved.
Walter M. Hosack, September 2025
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