Any ordinance must declare its intent, or goal. In this case, it must describe the specific purposes of open space preservation. These may include conserving agricultural lands or wildlife habitat, reducing municipal service costs, protecting wetlands or groundwater resources, preserving scenic, historic, or other important local character, or other valid public purposes. Appropriate purposes may include health, safety, property values, aesthetics, and many other interests where reasonable and properly motivated.
Be as clear as possible about this statement of intent. Include any detailed ordinance standard or guideline that may support it. Be cautious of requiring items that are not reasonably related to the intent.
In addition to a statement of intent, an OSD to retain rural character should address some or all of the components below. Other communities have included these for a variety of reasons. Consider each component alone, and how it may combine with others. Numbers here are for discussion, and will depend upon local circumstances and other ordinance components.
Ordinance defines resources or 'signature' lands that are an asset to be preserved in all instances.
OSD optional (as a special use) in all districts, and required in a sensitive areas overlay district.
Minimum of twenty-acre parcel, with minimum width (throughout) and road frontage of 200 feet.
Conventional residential plan must be accompanied by an OSD plan, for comparison during review.
OSD plan must be accompanied by an approvable conventional plan, to establish gross density.
Water, wetland, or roadway may not be construed as open space, or used to calculate gross density.
At least 60% of the entire site in permanently dedicated open space (preferably under PA 197, 1980).
At least 80% of open space in its natural state, and for passive use only.
Recreation improvements, if any (grass, grading, paths) in no more than 20% of open space.
Assurance (such as a perpetual easement) that open space can not be converted to other future uses.
Provision for access to the open space by all OSD lot owners (public access not a requirement).
Provisions for maintenance of the open space (by independent agency, township, or residents' group).
Minimum open space area is one acre; minimum open space dimension (width or depth) is 100 feet.
At least 60% of total open space linked as a unit (links must also be 100 feet wide).
Open space (100-foot minimum) as natural buffer between all lots and any pre-existing public road.
Open space (100-foot minimum) as natural buffer between all lots and any wetland or surface water.
Open space is functional for wildlife habitat, resource preservation, agricultural use, or recreation.
With on-site septic, lots at least 30,000 sq. feet, or 50% of district minimum, whichever is larger.
With public sewer, lots at least 15,000 sq. feet, or 25% of district minimum, whichever is larger.
Lots not larger than 150% of district minimum, unless required for on-site septic.
Lot frontage-to-depth ratios between 1:1 and 1:4.
Lot frontage at least 80 feet (internal roads only), or 50% of district minimum, whichever is larger.
Minimum building setbacks 10 feet, or 50% of district minimum, whichever is larger.
Lots not fronting on wetland or surface water (only open space may, at a minimum width of 100 feet).
No more than 50% of a lot, or 15,000 sq. feet, whichever is less, disturbed by development.
Lawns limited to 7,500 sq. feet, unless required to satisfy larger septic system needs.
Buildings placed at the edge of, or in the smallest tracts of, meadow, woods, or other signature areas.
Buildings not constructed on ridge lines, or otherwise blocking scenic views.
Buildings clustered, with their lots serving as buffer to open space.
No more than 10% of the entire OSD site disturbed for street and stormwater facilities.
Roads follow existing contours to minimize grading, and not located in signature areas.
Roads widths reduced to match lower traffic volumes on short driveway collectors.
Dwellings access interior roads directly, or share drives, and do not access pre-existing roads directly.
Total new road length less than one-half mile, or longest parcel dimension, whichever is less.
All utilities underground; no lot perimeter fencing or accessory buildings adjacent to open space.
Native species only in landscaped or recovered areas.
Overall design consistent in character with surrounding landscaping, traffic patterns, character.
Some specifics may not appear relevant to local conditions. However, remember that they may protect natural features now hidden from your view--or entirely unknown to anyone. Bulldozers are designed to go anywhere. Don't assume that an area is protected by its current owner, its isolation, or any other sacred character. Some people hold nothing sacred.
Specific ordinance elements may seem simpler in light of general OSD concepts.