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Open Space Design (OSD)/Natural Resource Protection Zoning (NRPZ)

In Brief: OSD/NRPZ is a tool to protect natural resources and open space. It includes elements of conservation subdivision regulations and cluster development bylaws and is used to regulate new subdivisions of land in a manner that maximizes the protection of natural resources (wetlands, forests, agriculture lands, open space) while providing for new construction and adequately compensating landowners.
The Problem
Thousands of acres of open space are developed in Massachusetts each year, much of it as residential sprawl. Unfortunately, in recent decades the rate of land development for homes and businesses has far exceeded the rate of population growth, meaning that more and more land is being used by fewer and fewer people. Sprawl development has contributed to a variety of problems for Massachusetts communities including loss of community character, a lack of diverse and affordable housing, social isolation of residents, and threats to natural resources and water quality.

Photo of sprawl
Introduction to OSRD/NRPZ
OSRD process graphic

The OSD approach begins with effective site planning which focuses on mapping of environmental resources to be preserved; identification of building areas which can support development economically and ecologically; and the use of design techniques to reduce impervious cover and impacts to water quantity and quality, such as clustering, permeable surfaces, reduced roadway pavement widths, and the preservation of natural drainage pathways.

Graphics: Arendt, Randall, 1996. Conservation Design for Subdivisions, Washington, D.C.

OSRD/NRPZ helps mitigate suburban sprawl impacts by addressing both open space/natural resource preservation and construction of housing. This technique is an innovative form of subdivision design that maximizes resource protection while providing economic profit. OSD provides the flexibility to allow various lot sizes, setbacks, and frontage within the development.

Characteristics of Open Space Design / Natural Resource Protection Zoning

NRPZ borrows from successful approaches used in other parts of the country to link significant land conservation to land development. The core concept behind NRPZ is the linking of low underlying densities with compact patterns of development so that significant amounts of land can be permanently protected and forever available for agriculture, forestry, recreation, water supply protection, carbon sequestration, and wildlife habitat.

A Creative Partnership Approach to Development. At the root of every OSD effort is a bylaw that facilitates residential development. OSD does not require a cumbersome permitting procedure but instead makes it quick and easy to build the type of project the community desires.

Consistency Between Boards and Departments: Because the NPRZ/OSD model zoning and subdivision regulations deal specifically with the site design process, communities should review and amend other local provisions (Wetlands Bylaws and Regulations, Board of Health Regulations, etc.) to avoid conflicts among boards, commissions, and departments. In addition, a community will benefit from close cooperation between other committees involved in natural resource based planning including Agricultural Commissions, Community Preservation Committees, and Open Space Committees.

Linking Density Bonuses to Community Goals: Ideally density bonuses will be directly linked to goals discussed in municipal planning documents, such as Planned Production (affordable housing), Open Space and Recreation, or Master Plans.

Linking Use of Open Space to Community Goals: Municipalities should carefully discuss the use and ownership of the open space to match local goals. Some communities will only want to allow passive uses of the open space, while others will want to allow active recreation. In many instances leaving the open space in private hands for agricultural or silvicultural use will be consistent with local goals.

Planning Board Understanding of Core Concepts: Communities adopting OSD zoning should be comfortable with the site analysis and conservation findings process. Where multiple resources on a single site may “compete” for protection, the Planning Board may need to prioritize or make suggestions to a proponent for alternative layout schemes. In addition, the Board should be open to a flexible design process that allows various lots sizes, frontages, and setbacks within the site design, rather than the usual "one size fits all" or “cookie cutter” approach.


Developers, landowners, conservation organizations, and municipalities alike support the practice of NPRZ/OSD. It allows a community to accomplish its land conservation goals, while building needed homes and treating developers and landowners equitably. In the short period of time since NRPZ was developed four communities have adopted the technique. Of note, NRPZ as provided for in this Toolkit addresses the flaws in cluster, open space residential, and other earlier zoning bylaws. A table on the last page of the model zoning outlines these flaws and current best practices.

In addition, implementing OSD/NRPZ in local subdivision development can successfully meet several of the Patrick Administration's Sustainable Development Principles including:

Concentrate Development and Mix Uses: The use of OSRD will concentrate development on to smaller areas of a site than what would generally happen under conventional zoning practice. It also provides flexibility to combine civic, educational, and recreational activities with open space and homes.

Make Efficient Decisions:The NRPZ permitting structure encourages smart growth and facilitates a permitting process that is clear, easy to understand, and cost-effective to developers.

Protect Land and Ecosystems: The planning process for NRPZ inherently protects land and water resources and promotes recharge to underlying aquifers. NRPZ also preserves significant cultural and historic resources.

Plan Regionally:Implemented on a broad scale, OSD/NRPZ can have significant regional impacts to watershed hydrology, wildlife habitat blocks and corridors, and aquifer protection.

Expand Housing Opportunities: OSD/NRPZ bylaws can expand housing opportunities in a community particularly where diverse housing types are allowed in a subdivision, a density bonus is available for the provision of affordable units, or when OSD/NRPZ is used in conjunction with inclusionary zoning.

Zoning pic

Financial Considerations
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OSD/NRPZis by-right, which means a guaranteed outcome and a streamlined plan review process.

OSRD like many other smart growth strategies, saves money for developers and municipalities by concentrating development and decreasing the necessity for and cost of installing and maintaining conventional infrastructure, such as lengthy and unnecessarily wide paved streets and stormwater management practices that collect and pipe runoff away from the site.

OSD/NRPZ also decreases site development costs by designing with the terrain. A minimum amount of clearing and grading is required, since the land with environmental constraints is preserved and removed form the developable area.

OSD/NRPZ adds valuable amenities that can enhance marketing and sale prices. Massachusetts subdivisions with a considerable amount of conserved open space have appreciated faster and increased their resale value more than conventional subdivisions. Well-designed OSD developments create higher property values than conventional developments with the same type of housing. This increase in value is the direct result of the better site amenities including open space, views, and preservation of historic resources.

Conservation Analysis Step One: Existing Conditions
Conservation Analysis Step Two: Site Constraints
Conservation Analysis Step Three: Identify Natural and Cultural Features
Conservation Analysis Step Four: Conservation Findings