Articles | Case Studies | Concept Tour

One of the most important question that must be answered by a community preparing to implement conservation development zoning is, “How will we determine the number of dwelling units permitted on a project?”. The number of units permitted in a standard subdivision is usually worked out on a map of the property, using the minimum lot size and road frontage set in the zoning. The project is laid out to provide homesites and roads that avoid unbuildable areas such as wetlands and steep slopes. However, much of the individual lots, particularly in large lot districts, overlaps these unbuildable areas. So a 3-acre lot may only have 1 buildable acre, the rest crossing a ravine or pond. Development projects in large-lot districts with a sizeable amount of unbuildable land may not see much net reduction in number of permitted units, because much of the minimum lot size can overlap the unbuildable area. In a ½ - acre lot district, however, the scenario changes, because at least 1/3 acre is needed for the homesite. Here, a large unbuildable area on a development property may result in a significant discount in number of units permitted, because so little of the permitted lots may overlap the unbuildable area.

How do these principles apply to conservation developments? A conservation development, by definition, applies the permitted density in the underlying zoning district. In some states, the developer is required to design a standard subdivision first, to prove the number of buildable units, and then design a conservation development using that number of units. In Ohio townships, we cannot make conservation development mandatory, so we avoid the map approach because it unduly extends the decisionmaking process, acting as a disincentive to developers. Instead, we rely on a formula laid out in the zoning code, which approximates the number of units that might be possible in a standard subdivision.

These formulae are highly individual, and must be tailored to the individual community. An example formula is given in the Countryside Program Resource Manual. However, a couple of interesting projects have brought to light the need to adjust our example for zoning districts with less than one acre minimum lot sizes.

The Countryside Program’s Model Regulation for Residential Conservation Development was originally set up for use in rural areas with very low underlying densities of at least 1 to 3 acres per unit. We designed an example density calculation formula that allows full density credit for unbuildable areas long as they did not exceed the amount of required open space. If they do, then the permitted density is discounted accordingly. This formula continues to work very well at lower densities in approximating the number of homes that are built in a standard subdivision. It also works well in higher-density districts where there is little or no unbuildable land.

However, a number of communities with higher underlying densities and large amounts of unbuildable land are using the model as well. For reasons discussed above, using the example formula in these areas results in a significantly higher number of permitted units than would be permitted in a standard subdivision. Over the last couple of months we have studied a number of subdivisions in these situations. As a result of our findings, we are in discussion about how we might adjust our example formula to better provide neutral density in small-lot zoning districts.

While we do not have a formula agreed upon yet, the formula proposed by Concord Township in Lake County for their R-1 district, with ½ acre lot sizes, might be useful. This formula removes 100% of unbuildable land: wetlands, floodway, and steep slopes over 25%; and removes 50% of isolated land (that can’t be built on due to intervening steep slopes or other barriers) before calculating density. They then add in a 10% adjustment to provide some “breathing room” for developers who might be penalized by the precision of the calculation. The result provides a reasonable incentive to the developer which still approximates the number of units that could be built under a standard subdivision.

As always, communities must carefully consider local conditions before adopting the appropriate density calculation. A properly devised density formula can result in a development pattern that conserves resources while providing for a high quality development of which everyone can be proud.