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Water: Best Management Practices

Open Space Design

Minimum Measure: Post-Construction Stormwater Management in New Development and Redevelopment

Subcategory: Innovative BMPs for Site Plans

Open space design, also known as conservation development or cluster development, is a better site design technique that concentrates dwelling units in a compact area in one portion of the development site in exchange for providing open space and natural areas elsewhere on the site. The minimum lot sizes, setbacks and frontage distances for the residential zone are relaxed in order to create the open space at the site. Open space designs have many benefits in comparison to the conventional subdivisions that they replace: they can reduce impervious cover, stormwater pollutants, construction costs, grading, and the loss of natural areas. However, many communities lack zoning ordinances to permit open space development, and even those that have enacted ordinances might need to revise them to achieve greater water quality and environmental benefits.

The benefits of open space design can be amplified when it is combined with other better site design techniques such as narrow streets, open channels, and alternative turnarounds (See fact sheets for Narrower Residential Streets, Eliminating Curbs and Gutters, and Alternative Turnarounds).


The codes and ordinances that govern residential development in many communities do not allow developers to build anything other than conventional subdivisions. Consequently, it may be necessary to enact a new ordinance or revise current development regulations to enable developers to pursue this design option. Model ordinances and regulations for open space design can be found on the Center for Watershed Protection Exit EPA Site website and in Better Site Design: A Handbook for Changing Development Rules in Your Community (CWP, 1998).

Open space design is widely applicable to most forms of residential development. The greatest stormwater and pollutant reduction benefits typically occur when open space design is applied to residential zones that have larger lots (less than two dwelling units per acre). In these types of large lot zones, a great deal of natural or community open space can be created by shrinking lot sizes. However, open space design may not always be a viable option for high-density residential zones, redevelopment, or infill development, where lots are small to begin with and clustering will yield little open space. In rural areas, open space design may need to be adapted, especially in communities where shared septic fields are not currently allowed by public health authorities.

Open space design can be employed in nearly all geographic regions of the country, with the result of different types of open space being conserved (forest, prairie, farmland, chaparral, or desert).

Siting and Design Conditions

Several site planning techniques have been proposed for designing effective open space developments (Arendt, 1996, and DE DNREC, 1997). Often, a necessary first step is adoption of a local ordinance that allows open space design within conventional residential zones. Such ordinances specify more flexible and smaller lot sizes, setbacks, and frontage distances for the residential zone, as well as minimum requirements for open space and natural area conservation. Other key elements of effective open space ordinances include requirements for the consolidation and use of open space, as well as enforceable provisions for managing the open space on a common basis.


A number of real and perceived barriers hinder wider acceptance of open space designs by developers, local governments, and the general public. For example, despite strong evidence to the contrary, some developers still feel that open space designs are less marketable than conventional residential subdivisions. In other cases, developers contend that the review process for open space design is more lengthy, costly, and potentially controversial than that required for conventional subdivisions, and thus, not worth the trouble.

Local governments may be concerned that homeowner associations lack the financial resources, liability insurance, or technical competence to maintain open space adequately. Finally, the general public is often suspicious of cluster or open space development proposals, feeling that they are a "Trojan Horse" for more intense development, traffic, and other local concerns. At the regional level, open space design policies and ordinances need to be carefully constructed and implemented so as not to lead to "leap-frogging," which is the creation of additional development in already built-up areas. An open space development that requires new infrastructure, such as roads, water and sewer lines, and commercial areas, can actually create more imperviousness at the regional level than it saves at the site level.

In reality, many of these misconceptions can be directly addressed through a clear open space ordinance and by providing training and incentives to the development and engineering community. The Natural Resources Defense Council presents several examples of successful conservation-oriented developments in Stormwater Strategies: Community Responses to Runoff Pollution (1999).

Maintenance Considerations

Once established, common open space and natural conservation areas must be managed by a responsible party able to maintain the areas in a natural state in perpetuity. Typically, the open space is protected by legally enforceable deed restrictions, conservation easements, and maintenance agreements. In most communities, the authority for managing open space falls to a homeowner or community association or a land trust. Annual maintenance tasks for open space managed as natural areas are almost non-existent, and the annual maintenance cost for managing an acre of natural area is less than $75 (CWP, 1998). It may be useful to develop a habitat plan for natural areas that may require periodic management actions.


Recent redesign research indicates that open space design can provide impressive pollutant reduction benefits compared to the conventional subdivisions they replace. For example, the Center for Watershed Protection (1998) reported that nutrient export declined by 45 percent to 60 percent when two conventional subdivisions were redesigned as open space subdivisions. Other researchers have reported similar levels of pollutant reductions when conventional subdivisions were replaced by open space subdivisions (Maurer, 1996; DE DNREC, 1997; Dreher and Price, 1994; and SCCCL, 1995). In all cases, the reduction in pollutants was due primarily to the sharp drop in runoff caused by the lower impervious cover associated with open space subdivisions. In the redesign studies cited above, impervious cover declined by an average of 34 percent when open space designs were utilized.

Along with reduced imperviousness, open space designs provide a host of other environmental benefits lacking in most conventional designs. These developments reduce potential pressure to encroach on resource and buffer areas because enough open space is usually reserved to accommodate resource protection areas. As less land is cleared during the construction process, the potential for soil erosion is also greatly diminished. Perhaps most importantly, open space design reserves 25 to 50 percent of the development site in green space that would not otherwise be protected, preserving a greater range of landscapes and habitat "islands" that can support considerable diversity in mammals, songbirds, and other wildlife.

Cost Considerations

Open space developments can be significantly less expensive to build than conventional subdivisions. Most of the cost savings are due to savings in road building and stormwater management conveyance costs. In fact, the use of open space design techniques at a residential development in Davis, California, provided an estimated infrastructure construction costs savings of $800 per home (Liptan and Brown, 1996). Other examples demonstrate infrastructure costs savings ranging from 11 to 66 percent. Table 1 lists some of the projected construction cost savings generated by the use of open space redesign at several residential sites.

Table 1. Projected construction cost savings for open space designs from redesign analyses

Residential Development

Construction Savings


Remlik Hall 1


Includes costs for engineering, road construction, and obtaining water and sewer permits

Duck Crossing 2


Includes roads, stormwater management, and reforestation

Tharpe Knoll 3


Includes roads and stormwater management

Chapel Run 3


Includes roads, stormwater management, and reforestation

Pleasant Hill 3


Includes roads, stormwater management, and reforestation

Rapahannock 2


Includes roads, stormwater management, and reforestation

Buckingham Greene 3


Includes roads and stormwater management

Canton, Ohio4


Includes roads and stormwater management

Sources: 1 Maurer, 1996; 2 CWP, 1998; 3 DE DNREC, 1997; 4 NAHB, 1986

While open space developments are frequently less expensive to build, developers find that these properties often command higher prices than homes in more conventional developments. Several regional studies estimate that residential properties in open space developments garner premiums that are 5 to 32 percent higher than conventional subdivisions and moreover, sell or lease at an increased rate. In Massachusetts, cluster developments were found to appreciate 12 percent faster than conventional subdivisions over a 20-year period (Lacey and Arendt, 1990). In Atlanta, Georgia, the presence of trees and natural areas measurably increased the residential property tax base (Anderson and Cordell, 1982).

In addition to being aesthetically pleasing, the reduced impervious cover and increased tree canopy associated with open space development reduce the size and cost of downstream stormwater treatment facilities. The resulting cost savings can be considerable, as the cost to treat the quality and quantity of stormwater from a single impervious acre can range from $2,000 to a staggering $50,000. The increased open space within a cluster development also provides a greater range of locations for more cost-effective stormwater practices. Clearly, open space developments are valuable from an economic as well as an environmental standpoint.


Anderson, L.M., and H.K. Cordell. Residential Property Values Improved by Landscaping With Trees. Southern Journal of Applied Forestry:162¿166.

Arendt, R. 1996. Conservation Design for Subdivisions: A Practical Guide to Creating Open Space Networks. American Planning Association Planners Book Service, Chicago, IL.

Center for Watershed Protection (CWP). 1998. Better Site Design: A Handbook for Changing Development Rules in Your Community. Center for Watershed Protection, Ellicott City, MD.

Delaware Department of Natural Resources and Environmental Control (DE DNREC) and The Environmental Management Center of the Brandywine Conservancy. 1997. Conservation Design for Stormwater Management. Delaware Department of Natural Resources and Environmental Control, Dover, DE, and the Environmental Management Center of the Brandywine Conservancy, Media, PA. 

Dreher, D.W., and T.H. Price. 1994. Reducing the Impacts of Urban Runoff: The Advantages of Alternative Site Design Approaches. Northeastern Illinois Planning Commission, Chicago, IL.

Lacey, J., and R. Arendt. 1990. An Examination of Market Appreciation for Clustered Housing with Permanently Protected Open Space. Center for Rural Massachusetts, Amherst, MA.

Liptan, T., and C.K. Brown. 1996. A Cost Comparison of Conventional and Water Quality-Based Stormwater Designs. City of Portland, Oregon, Bureau of Environmental Services, Portland, OR.

Maurer, G. 1996. A Better Way to Grow: For More Livable Communities and a Healthier Chesapeake Bay. Chesapeake Bay Foundation, Annapolis, MD.

National Association of Homebuilders (NAHB). 1986. Cost Effective Site Planning. National Association of Homebuilders, Washington, DC.

Natural Resources Defense Council (NRDC). 1999. Stormwater Strategies: Community Responses to Runoff Pollution. Natural Resources Defense Council, Washington, DC.

South Carolina Coastal Conservation League (SCCCL). 1995. Getting a rein on runoff: How sprawl and traditional towns compare. Land Development Bulletin (Number 7). South Carolina Coastal Conservation League, Charleston, SC.

Information Resources

Arendt, R. 1994. Rural by Design. American Planning Association Planners Book Service, Chicago, IL.

Montgomery County, Pennsylvania, Planning Commission. Guidelines for Open Space Management in the Land Preservation District. Montgomery County, Pennsylvania, Planning Commission, Norristown, PA.

Schueler, T.R. 1995. Site Planning for Urban Stream Protection. Metropolitan Washington Council of Governments, Washington, DC.

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