NOTE: All exhibits
and tables are located at the end of this text.
Shelter capacity is gross building area per acre that can be
occupied by any activity, assuming zoning and building code compliance. Sprawl results
from population growth that cannot survive without shelter for its many
activities, and an inability to correlate shelter capacity and activity with
average public revenue and expense per acre over defined municipal areas. This
prevents our ability to achieve a desired quality of life within areas that are
limited to protect their source of life.
My focus in this brief essay is to discuss: (1) the anatomy
of cities, (2) the cellular category we call single-family detached housing,
(3) the list of single-family cellular contents I refer to as design
specification topics, (4) the mathematical relationship of single-family design
specification topics, (5) the shelter capacity options produced when topic values
are modified, and (6) the measureable intensity levels produced by correlated topic
value decisions. The effort is based on my belief that we must begin to
understand, predict and correlate shelter capacity with activity, revenue, and
expense before we can lead the combination to form cities with a desirable
quality of life that are limited to protect their source
of life.
One of two building design categories can be chosen to
shelter single family residential activity. In order to proceed, I need to
explain these categories and their fit within a Built Domain classification
hierarchy that permits shelter measurement, evaluation, prediction and
knowledge to be accumulated, organized and taught on a consistent, comparable
basis that has the potential to improve our leadership performance.
THE ANATOMY of CITIES
Population growth has produced two worlds on a single
planet: The Built Domain and The Natural Domain.
The Built Domain is divided into Urban and Rural Phyla that
contain Shelter, Movement, Open Space, and Life Support Divisions. Each phylum
is distinguished by the significantly different areas associated with the same
divisions. (See Exhibit A for a more complete classification outline.)
The Shelter Division in both phyla is served by its
supporting Movement, Open Space and Life Support Divisions. Each cell in the
Shelter Division contains one of the eight building design categories listed on
lines 1-31 of Exhibit B. These categories are classified by their method of
parking supply, not their internal activity or external appearance. This makes
it possible to reconcile unique buildings into a common, limited set of
classification categories. The residential activity groups listed below line 33
in Exhibit B represent six of the many activity groups that can occupy a
limited list of building design categories.
Single-family detached residential activity is designated R1
and can occupy either the G1 or G2 Building Design Category. Table 1 applies to
the G1 Building Design Category when it is occupied by R1 activity and gross
land area is given. This table will be used to address discussion topics 2-6 previously
mentioned.
SINGLE-FAMILY
DETACHED HOUSING
The Reference Panel on lines 2-5 of Table 1 recites the
characteristics of seven common single-family lot sizes in columns C-J. These
lot sizes will be used as references for the remainder of this essay. Column C
represents an escape from earlier 15-30 by 100 foot or less lots created when land
ownership and the automobile made flight from a high density urban core
feasible. These small lots are now part of inner cities. They could not compete
with the larger 50x120, or 6,000 sq. ft., lots created in first ring suburbs
and noted in Column C.
The 6,000 sq. ft. lot typically contains a one-car detached
garage in the rear yard with a long access driveway that passes by the house
and through the rear yard. Social activity in the rear yard is compromised by
the garage and driveway presence. Fences often magnify rear yard insufficiency
in an effort to improve privacy.
The 60x120 foot lot in column D was an attempt to offer an
alternative to the smaller lots in Column C. It typically contains a two-car
garage that is either attached or detached. Detached garages still require
extended driveways and both still detract from a slightly larger rear yard.
Attached garages preserve the rear yard and require shorter driveways. Both still
seek to introduce rear yard privacy with fences on occasion.
Variance requests to expand home sizes with additions, add outdoor
social pavement, or connect to detached garages are often requested by owners
of Col. C-E lots. These variance requests reflect attempts to adapt to changing
lifestyle expectations with over-development and excessive impervious cover on
inadequate lot areas. This in turn can overwhelm storm sewer capacity when
repeated along a shared storm sewer line.
The 90x120 or 12,000 sq. ft. lot in Column G seems to
provide enough land area to meet current mainstream expectations regarding home
size, garage capacity, social pavement, service pavement, and privacy but
variance requests to expand can still reduce the unpaved open space percentage
that serves installed storm sewer capacity. Fence installations decline in
quantity when not prohibited.
The lot sizes in Columns G-J indicate increased affluence
and privacy. In general, increasing lot size increases the scope of sprawl per
dwelling and the movement, open space, and life support systems that must be extended
to serve it.
All lot sizes are subject to the impervious cover percentage
limits associated with installed storm sewer capacity. It is in a developer’s
interest to minimize initial sewer capacity and impervious cover potential to
serve only the initial installation in an effort to reduce cost. When this
occurs, it eliminates future home expansion potential and places unpaved open
space at risk of future expansion requests that seek to exceed the impervious
capacity of the storm sewer. It is in the public interest to record initial
impervious limit information for future reference when variance requests are
submitted, but this critical information is often overlooked, rarely compiled
on a city-wide basis, and unavailable for comparison with measured impervious
cover requests during variance proceedings.
The bottom line is that unpaved open space percentages and
impervious cover percentages are critical planning topics that must be
recognized and will be included with this discussion.
DESIGN SPECIFICATIONS
Table 1 illustrates the G1.R1.L1 Forecast Model listed on
line 36 of Exhibit B. Sixteen variable specification topics are identified with
boxes in three design specification modules. The Lot Module begins on line 9.
The Garage and Accessory Building Module begins on line 21. The Pavement Module
begins on line 31. Each box in a module must receive a specification value to
define the two-dimensional site planning characteristics of a housing proposal.
Nine specification boxes are provided in Col. A of the Planning Forecast Panel
to receive floor quantity options. These values complete the information needed
by the master equation in cell A44. It converts the maximum first floor area found
in cell G40 into nine home area options in cells B50-B58 based on these values.
In other words, sixteen two-dimensional specifications in the Land, Garage and
Pavement Modules of Table 1 are correlated with the nine floor quantity options
in the Planning Forecast Panel to produce the line item options presented in
the forecast panel. A change to one or more of the design specification values
in the three modules, or a change to one of the floor quantity options in the
Planning Forecast Panel, will produce a new forecast of implications in the
Planning Forecast Panel.
Lot Module
The Lot Module in Table 1 is based on a given lot size of
6,000 sq. ft. or 0.13774 acres in cell F10. The module subtracts a number of
potential demands on the gross lot area given to arrive at the buildable lot
area calculated in cell F17. An unpaved open space percentage is entered in
cell F18 and the remaining impervious cover is automatically calculated in cell
F19. The impervious cover percentage is used to calculate the amount of
buildable land that can be devoted to building and pavement cover in cell G19.
Garage and Accessory
Building Module
The five specification values entered in this module are
used to calculate the amount of impervious cover that is, or will be, consumed
by garage and accessory buildings in cell G29. This reduces the amount of
impervious cover remaining for first floor home area.
Pavement Module
The five specification values entered in this module are
used to calculate the amount of social and service pavement planned or present
around the home. The total pavement area is calculated in cell G38 and it too
reduces the amount of impervious cover remaining for first floor home area.
Home Footprint
When the available footprint area in cell G40 is multiplied
by the floor quantity options in cells A50-A58, the master equation in cell A44
calculates gross home area options in cells B50-B58, including any bonus area
above the garage. If cells F25-F27 are zero, there is no bonus area and the
reduced home area options calculated in cells C50-C58 will match the home area
options calculated in cells B50-B58.
The buildable land area remaining for building footprint was
found in cell G40 by subtracting the total support building and pavement areas
found in cell G39 from the total impervious area available in cell G19. The
remaining first floor or footprint area of 528 sq. ft. was the first indication
of an outdated lot area. The footprint was a function of the 30% impervious
cover available and the design specification values entered. The impervious
cover percentage limits future expansion, and I’ve seen more than 60% permitted
by variance approval when the storm sewer capacity is unknown. It’s very
difficult to say no to your neighbors when opinion cannot be answered with fact.
Shelter Capacity
Options
Shelter capacity (SFAC) is equal to total building area
(TBA) in sq. ft. divided by buildable lot area in acres (BLAC). When buildable
lot area (BLA) is expressed in sq. ft.:
SFAC = TBA / BLA / 43560. This can be reduced to:
SFAC = TBA * 43,560 / BLA
Home capacity per buildable acre (HCAC) does not include
garage and accessory building area. It is presented in Column G of the Planning
Forecast Panel of Table 1 but does not give an accurate impression of the total
building area contribution to site plan intensity. Total building area (TBA)
includes garage and accessory buildings in col. D and is used for this purpose.
Shelter capacity options are based on total building area (TBA) and presented
in Column H as one element of the intensity equation in cell J48. Both capacity
and intensity statistics are related to the floor quantity options in Column A.
As an example, a home with 2,000 sq. ft. of total building
area on ¼ acre equals a shelter capacity of 8,000 sq. ft. per acre. The same total
building area on 1/8 of an acre represents shelter capacity of 16,000 sq. ft.
per acre. This correlates land consumption with its shelter potential, and is one
element of the intensity equation in cell J48. If the occupant activity on both
land areas produced equal revenue per sq. ft., the 1/8 acre lot would produce
greater yield per acre but introduce much greater intensity.
INTENSITY
IMPLICATIONS
The acres within a city are its raw material. The shelter capacity
potential of each acre combines with occupant activity to determine the
productivity of each acre. From a public perspective, the average yield per acre
of municipal land area must equal or exceed its average expense to avoid budget
reductions. The push to increase shelter capacity per acre to increase yield
can produce excessive intensity that detracts from the quality of life a city
is attempting to afford, however. This means we need an improved method of
measuring, evaluating and correlating shelter capacity with occupant activity
because decisions at this land allocation level produce intensity, revenue and
context quantities that represent leadership decisions awaiting refinement by
talent.
Intensity (INT) is the relationship of building mass and
pavement to unpaved open space on a given land area in the Shelter Division of both
the Urban and Rural Phyla of the Built Domain. The intensity equation is noted
in cell J48 of Table 1. There is no attempt to pass judgement on the intensity
statistics presented in Col J of this table, but I have mentioned that the lot
size given in cell F10 is less competitive than the other options available to
this activity group on line 2 of the Reference Table. It also has the highest
density as shown on line 5.
Two and one-half stories has been a commonly accepted limit
for building height on suburban residential lot areas. Table 1 presents the
intensity produced by a 2.5 story building in cell J53 based on the sixteen values
entered in the design specification boxes above. The history of this lot size
and the intensity produced by the 2.5 story home specified provides a glimpse
of the measureable specification topics that can be compared, evaluated and
used to build leadership knowledge in the pursuit of sustainable cities with
symbiotic potential and a desirable quality of life.
OBSERVATIONS
I hope Table 1 has made it clear that it takes at least
sixteen correlated design specification values and one building height value to
accurately predict a single-family detached housing option with the master
equation in cell A44, and that this knowledge opens up a vast number of square
foot related predictions. A few of these have been included in the Planning
Forecast Panel of Table 1.
Zoning
Incomplete, independent and uncorrelated specifications
called zoning regulations often require choices among contradictions. When this
occurs, it requires variance approval to reconcile the choices made. The variances
approved are considered precedent setting, but they simply add confusion when
there is no comprehensive correlation of all regulations that combine to affect
shelter capacity and intensity. Contradictions in any endeavor simply frustrate
consistent leadership direction.
Home Size
Home sizes and lot sizes represent fixed decisions that can
last for centuries. Changing circumstances require adaptation that cannot be
accommodated easily, if at all. I chose the 6,000 sq. ft. lot in Table 1 to add
this point to the discussion. I could have chosen the 3,150 sq. ft. lot on page
23 of my book, The Science of City Design, but this would have been too
extreme for a brief discussion. The point is that both were desirable escapes
from the punishing density of central cities at one point in time. Time passes
however, and outdated home size can combine with outdated movement, open space,
and life support infrastructure to introduce intransigent decline. In some
limited cases this has been reversed when old neighborhood attributes become
desirable again; but for most, cities are saddled with decline they have yet to
solve with improved tools, knowledge and political determination.
Encircled Cities
Encircled cities without annexation potential often face
budget reductions and decline or increased taxation. The consequences of
encirclement have become apparent and have encouraged others to protect their annexation
corridors into agriculture and the Natural Domain. It is an unhealthy formula
that begins with a lack of data correlation that can lead to knowledge and
adjustment. Improvement will require that currently isolated data centers be
linked to a relational database with shelter forecast models that make land
management evaluation feasible and defensible.
Comparison of
Intensity Implications
I’m introducing Table 2 to make another point. The land area
given is 0.34435 acres, or 15,000 sq. ft. and is generally referred to as a 1/3
acre lot. The impervious cover limit calculated in cell F19 is 4,500 sq. ft.
when 70% unpaved open space is required in cell F18. This is the same open space
percentage entered in Table 1, but the percentage produces a significantly
higher impervious cover limit than the 1,800 sq. ft. in Table 1 because the lot
size is greater.
The same number of garage spaces and garage cover is
provided in Table 2, but a bonus habitable area over the attached garage has
been provided in cell F27 based on the specification values entered in cells
F25-26. After building cover and pavement are subtracted, the remaining
impervious cover available for home footprint is 2,718 sq. ft. in cell F40.
Based on the values entered in the design specification
template of Table 2, the 2.5 story home noted in cell A53 has a total home area
potential of 7,034 sq. ft. This is calculated in cell C53 using the master
equation in cell A44, and is significantly greater than the maximum home area
calculated in Table 1 for a 2.5 story home on a 6,000 sq. ft. lot.
A 7,034 sq. ft. home on a 15,000 sq. ft. lot would be far greater
than normal, but the 15,000 sq. ft. lot permits home expansion over time with a
30% storm sewer capacity. It simply permits too much. If, or when, the maximum
home size is constructed; it would produce an intensity of 0.613 as calculated
in cell J53 of Table 2 and be compatible with its neighbors. The intensity
calculated for the 6,000 sq. ft. lot in cell J53 of Table 1 is only 0.287, but
the 1,319 sq. ft. maximum home size is now considered less desirable.
Variances
The maximum home size permitted by 30% impervious cover on
the 6,000 sq. ft. lot in cell B53 of Table 1 may be less than desirable; but if
the neighborhood is desirable, it can prompt variance requests for building
additions and pavement that exceed 60% impervious cover. Under these
circumstances, shelter capacity will increase to 44,714 sq. ft. per buildable
acre, intensity will increase to 2.535, and the potential for flooding will
increase when adjacent neighbors demand equal treatment along the same sewer
line.
If low intensity on a small lot produces less intensity when
the impervious cover limit is respected, but much greater intensity when
variances are granted to exceed this limit, how should lot size be addressed
for a building design category and activity group that consumes the most land
per occupant sheltered in urban areas? Keep in mind that lot size has been a
major contributor to both inner city blight and suburban sprawl. A free market
has sought relief from excessive intensity with this residential concept, but
it rarely produces enough revenue per acre to offset a city’s average expense
per acre over an extended period of time without increased taxation and budget cuts.
Unpaved Open Space
Implications
If I prepared tables for ½ acre and 1 acre lots with similar
30% unpaved open space specifications, theoretical shelter capacity and
intensity for a 2.5 story home would continue to increase from the 15,000 sq.
ft. lot in Table 2. The ½ acre lot would produce 24,381 sq. ft. per acre and an
intensity of 0.731. The one acre lot would produce 26,892 sq. ft. per acre and
an intensity of 0.807, but these intensity measurements are going in the wrong
direction. An increasing lot size is expected to produce less intensity.
The intensity increase occurs because the 70% unpaved open
space provision has not been increased with the increasing lot sizes. If it
isn’t, 30% impervious cover on a larger lot size will permit greater potential
shelter capacity and intensity per acre. This doesn’t happen because maximum
potential home sizes are rarely built on larger lots, but the intent to
decrease intensity by increasing lot size is left to chance.
Home Sizes
I’m including Table 3 to illustrate an obvious design
principle. The table is based on a given home area with an unknown lot area to
be found. The Lot Module explains that the land area basis for calculation is
70% unpaved open space and 30% impervious cover. A number of specification
values have been entered in the Building Module to arrive at a total home area
objective of 2,148 sq. ft. in cell F23. The 100 sq. ft. accessory building area
entered in cell F24 is added to the home area to find the total building area
of 2,728 sq. ft. in cell F25. The specification values entered in the Pavement
Module are used to find the driveway and parking pavement areas in cell F34.
These values complete the information needed by the master equation in cell
A37. (I should mention that this master equation is equal to the equation on
page 48, line 56 of my book[1],
but it does a better job of differentiating building cover from pavement
cover.)
The Planning Forecast Panel predicts that a one story home
with the specification values entered would require a 12,000 sq. ft. lot in
cell B43, and that this would produce an intensity of 0.297 with a shelter
capacity of 9,901 sq. ft. per acre. A 2.5 story home would only need a 7,761
sq. ft. lot as shown in cell B46, but would produce an intensity of 0.362 and a
shelter capacity of 12,054 sq. ft. per acre. In other words, the trade-off for
greater shelter capacity per buildable acre is increased floor quantity and
greater intensity. The choice is a very serious issue because the management of
shelter capacity, intensity and context for all building design categories and
activity groups will determine our ability to correlate our presence on a
planet with limited capacity.
Setback Lines
Someone may comment that intensity hasn’t been left to
chance because front, side and rear yard setback requirements increase with
lower density zoning districts, and this hasn’t been taken into account. I have
empirically found that setbacks increase yard areas with increased dimensions,
but these dimensions do not consistently reduce shelter capacity and intensity.
They only appear to be correlated and may be occupied by buildings and pavement
that reduce their off-setting benefit. From a designer’s perspective, setbacks are
primarily useful for building alignment when desired, fire separation when
adequate, and privacy when generous. They are no substitute for adequate unpaved
open space quantities defined and correlated with design specifications that
establish the format for shelter capacity, intensity and context refinement.
Intensity Correlation
Table 4 shows how intensity increases in cells F12-17 when shelter
capacity per acre increases in cell B12-17. The intensity noted in cell F12 is
related to the 6,000 sq. ft. lot introduced by Table 1. Cell F17 is based on a
similar specification when a one acre lot is given. The intensity statistics
are going in the wrong direction because the design specifications for all lots
have been held constant, and a larger lot with the same impervious cover
percentage will produce greater building and pavement area that results in
greater potential intensity. This can be easily corrected when an unpaved open
space percentage is increased with lot size in a design specification template,
or when other adjustments are introduced to reflect the lifestyle associated
with increased lot sizes. This resolves one issue, but it does not begin to
address the excessive consumption of agriculture and the Natural Domain for
increasing lot sizes.
CONCLUSION
This essay has focused on site plan quantities defined by
the values entered in a design specification template. This is a tactical
project issue. The strategic question involves the cellular aggregations that
combine to form neighborhoods and districts within a city. The land use
allocation of shelter capacity, activity and intensity must produce average
revenue per acre that meets or exceeds its average expense per acre for
operations, maintenance, improvement, and debt service without excessive
intensity. Strategic answers will require data accumulation, correlation, and
land management that is beyond the scope of this brief essay. Physical, social
and financial balance is feasible, however, when specification templates are
linked to each parcel of land within a city and correlated with other data
sources to form a complete picture of a city’s current physical, social, and financial
condition. This will permit comprehensive evaluation and adjustment with the
credibility required to convince others. Planning leadership for a sustainable
future cannot proceed without a scientific bridge language capable of relating
population and activity to its shelter imperative on a planet with limited
resources that demands symbiotic relationships.
We have been preoccupied with growth to counter risk and
threat since the beginning of time. This is the origin of the admonition to be
fruitful and multiply. We have been successful. It is time to recognize that success
from growth is the enemy of balance, and we must adapt to a new level of symbiotic
responsibility. The planet is programmed to seek its own balance. I think we
intuitively understand that the same law applies to us, but it requires
anticipation without proof by extinction. This is a requirement of faith by any
name. In fact, faith-based names have distracted us from reality. God has given
us the planet. This power has not assigned ownership. It has assigned
responsibility. It is up to us to define what that means and adapt accordingly.
Copyright: Walter M. Hosack, 2017. All Rights Reserved
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