Open space design is a form of residential development that concentrates development in a compact area of the site to allow for greater conservation of natural areas. This form of development may also be called cluster design, conservation design, or low impact development (LID). Many of the typical management practices associated with open space design and LID including Reducing Impervious Surfaces, Pervious Pavements, Green Roofs, Rainwater Harvesting, Urban Forestry, Vegetated Swales and Buffers, and Establishing an Infiltration Standard are presented within this guidance document. This fact sheet presents guidance on the development of an ordinance to encourage the use of open space design and LID
Research has shown that open space designs can more effectively reduce a site’s overall impervious cover compared to conventional subdivisions, and command higher prices and more rapid sales because of the attraction of open space and preserved natural features (Zielinski, 2001). Other benefits include lower costs for grading, erosion control, stormwater and site infrastructure, as well as greater land conservation, without the loss of developable lots. Increased open space and less runoff directly translates into lower pollutant loads to downstream waters, protecting lakes, streams and wetlands. This is especially true when the preserved open space is tied into a well designed overall site runoff management plan. Open space design can revitalize city centers, increase the quality of life of its citizens and attract tax-paying businesses and residents to the area.
Open space design is a form of development that allows for greater conservation of natural areas. Approaches include relaxed minimum lot sizes, setbacks and frontage distances in order to maintain the same number of dwelling units at the site while creating more open space.
A mixed-use approach that integrates usable grassed park space with a trail system among restored native ecosystems and preserved drainageways and wetlands can be a very effective approach. Shared driveways and utilities is one example of impervious surface reduction that can facilitate the preservation of open space.
The residential development Fields of St. Croix, in Lake Elmo, MN, was completed in 2004 and is an example of open space design. The development includes 113 single family homes and 12 attached single family homes with lot sizes ranging from 0.35- to 1-acre. The 241-acre site leaves 144 acres (60 percent) as open space. The development maximized open space using cluster development techniques. Street widths are sized appropriate to their function ranging from 14-foot one-way lanes to 24-foot two-way lanes. More than 90 acres of farmland are preserved and functions as a community-supported agricultural farm with paying members. Additional open space consists of prairie and oak savanna and a pond and associated preserved shoreland. The site also uses a constructed wetland wastewater treatment system for the entire development.
For additional design techniques that identify ways to preserve more open space (e.g. smaller parking lots, slimmer sidewalks and streets), see the Reducing Impervious Surfaces fact sheet.
Open space design and LID practices are not limited to new construction. Most of the techniques can be done on existing developed land. For example, the cities of Maplewood and Burnsville both successfully incorporated a rain garden network into existing neighborhoods to capture street runoff, reducing the amount of runoff generated locally. In the case of Maplewood, this approach was chosen over more traditional curb and gutter installation. The LID approach can also be employed to comply with local regulations governing the volume, rate, and quality of runoff. See the Retrofitting: Infiltration, Filtration & Bioretention fact sheet for more information.
Development rules can be in conflict with alternate design standards that maximize the amount of open space associated with a development. Development rules can refer to subdivision codes, zoning regulations, parking and street standards and other local ordinances that regulate development. These rules will likely require review and adjustment to allow for open space design. Municipal fire, police and public works operations (ex. snow plowing) must be an integral part of the rule/ordinance planning so that their perspective is incorporated into any changes being considered. Material provided in the Additional Resources can help to address some of the concerns (fire truck access, snow storage) often raised by these departments.
The open space ordinance in the City of Inver Grove Heights’ Northwest Area requires 20 percent of upland buildable area (excluding area dedicated to stormwater treatment, protected wetlands, and other non-buildable space) to be maintained as undisturbed, natural area. In addition, the code allows an increased mixture of housing types for each zoning district in order to promote and enable cluster development to facilitate open space design.