More than 1.5 million acres of land are developed each year in the United States. In most
communities, this development consists of many individual projects built over decades.
The cumulative amount of land development can transform the landscape within a
community. Development alters the surface of the land, by replacing natural cover with
roof tops, roads, parking lots, driveways and sidewalks. These hard surfaces are
impermeable to rainfall and are collectively known as impervious cover.

Recent watershed research has shown that impervious cover can have a negative impact
on the quality of our nation's aquatic resources. The influence of impervious cover on
aquatic systems presents a challenge to communities interested in sustainable
development.

Communities have long struggled to achieve the goal of sustainable development—
economic growth that also protects the local environment. Indeed, many communities
have found that their own development codes and standards can actually work against
sustainable development. For example, local codes and standards often create needless
impervious cover in the form of wide streets, expansive parking lots and large-lot
subdivisions. At the same time, local codes often give developers little or no incentive to
conserve natural areas that are so important for watershed protection. Consequently,
communities may want to reevaluate their local codes to ensure that they produce more
sustainable development.  Click here to use our Codes and Ordinances Worksheet to
evaluate your own community.

As members of the Site Planning Roundtable, we have worked for two years to craft
model principles to guide better land development. We are a wide and diverse group of
individuals involved in planning, designing and building new communities and protecting
the natural environment. It is our contention that better development can only be achieved
if we fundamentally change the way that land is developed— by reducing impervious
cover, conserving natural areas and preventing stormwater pollution.

To this end, we have brought our technical and real world experience together through a
consensus process in an effort to create more environmentally sensitive, economically
viable and locally appropriate development. We have developed a set of twenty-two model
development principles for consideration by local planners, developers, lenders and
environmental groups. Applied together, the model principles can measurably reduce
impervious cover, conserve natural areas and prevent stormwater pollution from new
development. In addition, the model principles can enhance the value of our
neighborhoods and enrich the quality of life in our communities. With this in mind, the
model principles should be considered as a starting point when evaluating current local
codes, and should be interpreted in the context of the Technical Support Document upon
which they were derived.
 

Key Points of Consensus

     Meaningful changes in how development occurs can only happen when local
     concerns regarding safety, fire protection, liability, economics, market acceptance,
     and quality of life are thoroughly satisfied.
     Model development principles are needed to guide better land development and to
     act as a benchmark to assess current zoning, parking, street and subdivision
     codes.
     Model development principles must also enhance the quality of life within a
     community as well as protect natural and aquatic resources.
     Model development principles must be implemented as part of a flexible,
     locally-adapted strategy for better site planning and are not a national "one-size fits
     all" standard.
     The model development principles should be consistent with larger community
     goals (both economic and environmental) that are put forth in comprehensive
     growth management, resource protection, or watershed management plans.
     Where possible, infill and redevelopment should be encouraged to reduce the
     amount of new impervious cover created in the landscape and create a more
     compact development pattern.
     It is recognized that the model principles must be adapted to reflect the unique
     characteristics of each community, not all principles apply to every development
     site, and some principles may not always fully complement each other.

To this end, we have combined our technical, professional, and real world experiences to
craft twenty-two model development principles that identify for local planners and zoning
officials key benchmarks for measurably reducing the amount of impervious cover created
by new development.
 

Site Planning Roundtable Model Development Principles

The twenty-two model development principles provide design guidance for economically
viable, yet environmentally sensitive development. Our objective is to provide planners,
developers, and local officials with benchmarks to investigate where existing ordinances
may be modified to reduce impervious cover, conserve natural areas, and prevent
stormwater pollution. These development principles are not national design standards.
Instead, they identify areas where existing codes and standards can be changed to better
protect streams, lakes and wetlands at the local level. The development principles are
divided into the three following areas:

     Residential Streets and Parking Lots (Habitat for Cars)
     Lot Development (Habitat for People)
     Conservation of Natural Areas (Habitat for Nature)

Each principle is presented as a simplified design objective. Actual techniques for
achieving the principle should be based on local conditions. Please consult the Technical
Support Document for more detailed rationale for each principle.

Residential Streets and Parking Lots (Habitat for Cars)

                     1. Design residential streets for the minimum required
                     pavement width needed to support travel lanes; on-street
                     parking; and emergency, maintenance, and service vehicle
                     access. These widths should be based on traffic volume.
                     2. Reduce the total length of residential streets by examining
                     alternative street layouts to determine the best option for
                     increasing the number of homes per unit length.
                     3. Wherever possible, residential street right-of-way widths
                     should reflect the minimum required to accommodate the
                     travel-way, the sidewalk, and vegetated open channels.
                     Utilities and storm drains should be located within the
                     pavement section of the right-of-way wherever feasible.
 

                     4. Minimize the number of residential street cul-de-sacs and
                     incorporate landscaped areas to reduce their impervious
                     cover. The radius of cul-de-sacs should be the minimum
                     required to accommodate emergency and maintenance
                     vehicles. Alternative turnarounds should be considered.
                     5. Where density, topography, soils, and slope permit,
                     vegetated open channels should be used in the street
                     right-of-way to convey and treat stormwater runoff.
                     6. The required parking ratio governing a particular land use
                     or activity should be enforced as both a maximum and a
                     minimum in order to curb excess parking space
                     construction. Existing parking ratios should be reviewed for
                     conformance taking into account local and national
                     experience to see if lower ratios are warranted and feasible.
                     7. Parking codes should be revised to lower parking
                     requirements where mass transit is available or enforceable
                     shared parking arrangements are made.
                     8. Reduce the overall imperviousness associated with
                     parking lots by providing compact car spaces, minimizing
                     stall dimensions, incorporating efficient parking lanes, and
                     using pervious materials in spillover parking areas where
                     possible.
                     9. Provide meaningful incentives to encourage structured and
                     shared parking to make it more economically viable.
                     10. Wherever possible, provide stormwater treatment for
                     parking lot runoff using bioretention areas, filter strips, and/or
                     other practices that can be integrated into required
                     landscaping areas and traffic islands.
 
 
 

Lot Development (Habitat for People)

                     11. Advocate open space design development incorporating
                     smaller lot sizes to minimize total impervious area, reduce
                     total construction costs, conserve natural areas, provide
                     community recreational space, and promote watershed
                     protection.
                     12. Relax side yard setbacks and allow narrower frontages to
                     reduce total road length in the community and overall site
                     imperviousness. Relax front setback requirements to
                     minimize driveway lengths and reduce overall lot
                     imperviousness.
                     13. Promote more flexible design standards for residential
                     subdivision sidewalks. Where practical, consider locating
                     sidewalks on only one side of the street and providing
                     common walkways linking pedestrian areas.
                     14. Reduce overall lot imperviousness by promoting
                     alternative driveway surfaces and shared driveways that
                     connect two or more homes together.
                     15. Clearly specify how community open space will be
                     managed and designate a sustainable legal entity
                     responsible for managing both natural and recreational open
                     space.
                     16. Direct rooftop runoff to pervious areas such as yards,
                     open channels, or vegetated areas and avoid routing rooftop
                     runoff to the roadway and the stormwater conveyance
                     system.
 

Conservation of Natural Areas (Habitat for Nature)

                     17. Create a variable width, naturally vegetated buffer system
                     along all perennial streams that also encompasses critical
                     environmental features such as the 100-year floodplain,
                     steep slopes and freshwater wetlands.
                     18. The riparian stream buffer should be preserved or
                     restored with native vegetation. The buffer system should be
                     maintained through the plan review delineation, construction,
                     and post-development stages.
                     19. Clearing and grading of forests and native vegetation at a
                     site should be limited to the minimum amount needed to
                     build lots, allow access, and provide fire protection. A fixed
                     portion of any community open space should be managed as
                     protected green space in a consolidated manner.
                     20. Conserve trees and other vegetation at each site by
                     planting additional vegetation, clustering tree areas, and
                     promoting the use of native plants. Wherever practical,
                     manage community open space, street rights-of-way,
                     parking lot islands, and other landscaped areas.
                     21. Incentives and flexibility in the form of density
                     compensation, buffer averaging, property tax reduction,
                     stormwater credits, and by-right open space development
                     should be encouraged to promote conservation of stream
                     buffers, forests, meadows, and other areas of environmental
                     value. In addition, off-site mitigation consistent with locally
                     adopted watershed plans should be encouraged.
 

                     22. New stormwater outfalls should not discharge
                     unmanaged stormwater into jurisdictional wetlands,
                     sole-source aquifers, or sensitive areas.
 

Recommendations

     We affirm our support for the model development principles and the Technical
     Support Document upon which they are based.

     We encourage local governments to consider these principles when evaluating their
     local zoning codes, subdivision ordinances, and landscape ordinances.

     We encourage the development community to incorporate these model
     development principles in their land development projects.

     We encourage the formation of local roundtables to adopt and adapt these model
     development principles within the context of local growth and environmental
     protection goals.

     We encourage the lending and insurance communities to consider these principles
     and examine their role in land development.

     We encourage local, state, and federal agencies to provide the technical support,
     financial incentive, and regulatory flexibility needed to promote the model
     development principles.

     We encourage environmental and watershed organizations and the general public to
     use these principles as educational tools.

Acknowledgements

The Site Planning Roundtable would not have been possible without the generous support
of our funders.

     The Morris and Gwendolyn Cafritz Foundation
     US EPA Office of Wetlands, Oceans, and Watersheds
     Chesapeake Bay Trust
     Turner Foundation
     Chesapeake Bay Program
 

We would also like to thank the individuals who served as chairs of the Research
Subgroups:

Lisa Fontana - Institute of Transportation Engineers
Residential Streets and Parking Lots
Roger Platt - National Realty Committee
Conservation of Natural Areas
Richard Claytor - Center for Watershed Protection
Lot Development

CWP Site Planning Roundtable Team Members:
Chris Swann, Jennifer Zielinski, Deb Caraco, and Hye Yeong Kwon.

References

Arendt, R. 1994. Designing Open Space Subdivisions.
Booth, D. 1991. Urbanization and the natural drainage system-impacts, solutions and
prognoses. Northwest Environmental Journal. 7(1):93-118.
Chesapeake Bay Foundation. 1996. Growth, Sprawl, and the Bay: Simple Facts About
Growth and Land Use.
Leinberger, C. 1995. "Metropolitan Development Trends of the Late 1990s: Social and
Environmental Implications."
Taylor, B.L. 1993. The influences of wetland and watershed morphological characteristics
and relationships to wetland vegetation communities. Masters thesis. Dept. of Civil
Engineering. University of Washington. Seattle, WA.
Urban Land Institute. 1992. Density by Design.
Urban Land Institute. 1997. America's Real Estate.
Wells, C. 1995. Impervious Surface Reduction Study: Final Report. City of Olympia Public
Works Department. Water Resources Program. Olympia, WA.

Full color, hardcopy versions of this report are available from the Center
for Watershed Protection for $3 per copy. A Technical Support Document, Better Site
Design: A Handbook for Changing Development Rules in Your Community, is available
from the Center for $35.