Open Space Development

Open space development, also known as cluster development, is a site planning technique that arranges buildings and infrastructure in a compact portion of a development site to preserve the remaining land as undeveloped open space. This approach minimizes impervious cover, reduces the extent of clearing and grading, and protects natural resources. By concentrating development, this zoning model allows for the same number of dwelling units as a conventional subdivision while significantly reducing the overall environmental impact and preserving community character.

This model ordinance provides a regulatory framework for implementing open space development as a standard practice. It is designed to be density-neutral, meaning it does not reduce the total number of allowable housing units on a parcel but rather reconfigures their layout. The ordinance establishes clear standards for the amount, quality, and long-term management of the preserved open space. The goals are to reduce stormwater runoff and pollutant loads, protect sensitive environmental features like stream buffers and forests, lower infrastructure costs, and provide community amenities. It offers a flexible yet structured alternative to conventional lot-by-lot subdivision regulations.

Key provisions

Applicability

The provisions of this ordinance apply to all residential zones with a base density of eight dwelling units per acre or less. To be eligible, a development site must have a minimum size of five acres. The model frames open space development as a “by-right” option, meaning a plan that meets the ordinance’s requirements follows the standard approval process and cannot be denied in favor of a conventional layout. Plats that were officially registered before the ordinance’s adoption are exempt from its requirements.

Density and Dimensional Standards

The ordinance is designed to be density-neutral, ensuring that a developer can build the same number of units as would be permitted under conventional zoning. The total number of allowable units is calculated using a “partial density transfer” formula, which applies the base density to the buildable area of the site (total area minus unbuildable lands and rights-of-way).

To achieve the clustered design, the ordinance allows for significant flexibility in dimensional standards. Frontage distances and yard setbacks (front, rear, and side) may be reduced by up to 50% of the requirement in the underlying zone, with specified minimums (e.g., 10 feet for front setbacks, 5 feet for sideyards). Minimum lot sizes can be reduced to 25% of the base zoning requirement, but no smaller than 1/8 of an acre. The ordinance also explicitly permits irregular lot shapes and shared driveways, which are key components of efficient cluster design. Shared septic systems and alternative parking arrangements (e.g., on-street parking) are also permitted, subject to approval by the relevant local departments.

Open Space Requirements

A core component of the ordinance is the requirement to set aside a meaningful portion of the site as permanent open space. The required percentage of open space increases as the base density of the zone decreases, reflecting the greater feasibility of preservation on larger lots. The following table outlines the minimum requirements.

The ordinance specifies that certain areas cannot be counted toward the required open space, including unbuildable lands (wetlands, steep slopes, floodplains), existing rights-of-way, and private lawns or setbacks. It establishes high-priority areas for inclusion in the open space, such as resource buffers, high-quality forests, critical habitats, and prime soils. To ensure the open space is functional and ecologically valuable, at least 75% of it must be in a contiguous block, and at least 50% must be designated as “green space” to be maintained in a natural, undisturbed condition. The remaining “community space” can be used for passive or active recreation or for Stormwater Management facilities designed according to the local Design Manual. Impervious cover within active recreation areas is limited to 5%.

Ownership and Management

Ensuring the permanent protection of the designated open space is a critical function of the ordinance. Development in these areas is permanently prohibited. The model provides three primary options for ownership and long-term management:

1. Homeowner’s Association (HOA): Ownership is shared among the individual lot owners, who are mandatory members of an HOA responsible for managing and maintaining the open space.
2. Conservation Easement (to Municipality): The open space is owned by a separate entity (such as the HOA), but a legally binding conservation easement is granted to the municipality to enforce the preservation restrictions.
3. Conservation Easement (to Land Trust): The conservation easement is transferred to a qualified non-profit land trust organization whose mission includes land conservation. This option is recommended for natural areas and requires that the organization is acceptable to the planning agency.

Regardless of the ownership structure, an open space management entity must be established to prescribe allowable uses, provide maintenance standards, and ensure the space is protected in perpetuity. The boundaries of all open space areas must be clearly delineated on all plans and marked in the field.

Selected provisions, annotated

Open space is a by-right form of development, and shall not require a special exception or additional review.

Model Open Space Ordinance, Section III.C

This provision makes open space development a predictable and administratively straightforward option for developers. By avoiding a lengthy and uncertain special exception or variance process, the “by-right” approach encourages the use of this environmentally preferable design without creating extra hurdles compared to conventional development.

At least 50% of designated open space shall be designated as “green space” as defined in Section II and shall be maintained in a natural, undisturbed condition.

Model Open Space Ordinance, Section V.E

This clause ensures that a significant portion of the preserved land serves a direct ecological function. While some open space can be used for recreation or stormwater facilities, this requirement guarantees the protection of natural habitats, promotes infiltration, and contributes to the goals of ordinances for Forest Conservation and Stream Buffers.

The conservation easement shall… Protect open space from future development and environmental damage by restricting the area from any future building and against the removal of soil, trees, and other natural features, except as is consistent with conservation, recreation, or agricultural uses…

Model Open Space Ordinance, Section VI.B.3.a

This language defines the fundamental purpose of the legal mechanism used to protect the open space. A conservation easement is a permanent, legally enforceable restriction on the use of the land, ensuring that the conservation and community benefits of the open space are not compromised by future landowners or changing development pressures.

What makes it a useful model

This ordinance serves as a strong model because it is built on the principle of density neutrality. By allowing the same number of homes as conventional development, it removes a primary economic objection from landowners and developers, making it a more politically viable tool. It focuses on reconfiguring development rather than reducing it, which can be a crucial distinction in jurisdictions concerned with private property rights and maintaining development potential.

The model provides clear, quantitative standards that create a predictable regulatory environment. Specific percentages for required open space, minimums for contiguous areas, and limits on impervious surfaces make the requirements easy to understand and enforce. This clarity reduces ambiguity for both municipal reviewers and site designers. Furthermore, the ordinance directly addresses the critical issue of long-term stewardship by requiring a formal management plan and providing several legally robust options for ownership and oversight, such as HOAs and conservation easements held by a municipality or land trust. This foresight helps prevent the common failure of designated open spaces falling into neglect.

Finally, the model explicitly links open space preservation with broader watershed protection goals. By prioritizing the inclusion of sensitive resources like forests, wetlands, and stream buffers within the preserved areas, it ensures that the open space is not just leftover land but is strategically designated to maximize ecological benefits. This makes it an effective companion to other environmental regulations in a municipality’s code, which can be found in the Model Ordinances library.

Adaptation checklist for municipalities

When adapting this model ordinance for local use, municipalities should address the following key elements:

• Define the specific local planning agency and other relevant departments (e.g., Health Department, Fire Department) responsible for review and approval.
• Specify the exact residential zoning districts to which the ordinance will apply.
• Determine the appropriate legal pathway for open space development: “by-right” (as in the model), by special exception, or as a mandatory requirement in certain districts.
• Calibrate the density calculation formula, deciding whether to use the “partial density transfer” in the model or a “full density transfer” based on local density and conservation goals.
• Review and adjust the table of required open space percentages to align with the community’s specific zoning categories and land use patterns.
• Establish a clear and locally relevant definition of “unbuildable land,” referencing specific local constraints such as steep slope ordinances, floodplain maps, and regulations for Wetlands Protection.
• Reference the official municipal or state stormwater design manual that must be followed for any stormwater facilities located within the community open space.
• Establish criteria for approving non-profit land trust organizations as eligible holders of conservation easements.
• Incorporate or reference specific local standards for road widths, utility easements, sidewalks, and signage for open space areas.
• Develop a standard model conservation easement document that conforms to state and local legal requirements.
• Ensure the provisions are harmonized with other local codes, including subdivision regulations, zoning, and other natural resource protection ordinances.