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PLAIN ECONOMIC SENSE
For release after Dec. 21, 1998
Column 360
Increasing Development Density to Reduce Urban Sprawl
By Mark A. Edelman
Extension Public Policy Economist
Iowa State University Extension to Communities
What strategies are used to encourage higher density residential development on the rural-urban fringe? Most cities and counties can use their planning and zoning ordinances. New developments must typically go through a preliminary site plan and final plat approval process to make sure the new development proposal fits within the parameters in the local zoning code.
For example, an R-1 designation in one typical city code restricts new homes in R-1 districts to single family dwellings. It requires a minimum lot size of 11,000 square feet, a minimum lot width of 80 feet, and a minimum side yard of 9 feet. A side yard is the distance from the side of a house to the property line. Houses are 18 feet apart if the side yards are 9 feet.
An R-2 designation in the same city requires a minimum lot size of 8,500 square feet for single family homes or 12,000 square feet for duplexes. The minimum lot widths are 65 feet for the single family dwelling and 70 feet for duplexes. Nine foot side yards are required.
An R-3 designation for the same community requires a minimum lot size of 7,000 square feet for single family dwellings, 8,000 square feet for duplexes, and 2,500 addition square feet for each family unit over two. Minimum lot widths are 60 feet for the single family dwellings and duplexes and 100 feet for other multiple-family dwellings. Nine foot side yards are required.
The community's R-4 designation is a mobile home district. It requires a 5,500 minimum lot size, a 55 foot lot width, and 5 foot side yard.
Note that most zoning parameters are typically stated in terms of minimums. Above the minimum parameters, developers, builders and customers decide the lot sizes and widths to be incorporated into the new development plans based on the segment of the housing market targeted by the developer and the development costs. Lot widths and side yard requirements are important because street and public infrastructure costs run about $200 per lot frontage foot.
The primary stated purpose of the zoning ordinance is to protect property owners from incompatible uses that might threaten the value, use or enjoyment of property in the zoning district. In general, people typically become upset when someone builds a neighboring home that detracts from the value of their property. That's why minimums typically are included in the zoning codes. Few people are upset when someone builds a larger, more expensive home next door, because it adds value to the neighborhood.
Because of recent urban sprawl and land use concerns, the state could provide regulatory or financial incentives to encourage local city and county officials to set lot size goals, add maximum lot size and width parameters to the existing zoning districts and/or create new zoning districts with higher density parameters. For example, Altoona recently debated a 55-foot wide development for 200 houses. While this concept would encourage more density and less sprawl compared to other developments, news reports indicate the proposal was turned down because neighboring property owners were concerned about eroding property values.
Smaller lots are not always correlated with lower home values. Ames has been implementing a new zoning district referred to as the "village concept." Higher value homes conforming to unique standards are sited on narrow lots to conserve land and infrastructure costs.
In addition, many communities have adopted a zero lot line option for duplexes and condominiums. Building plans that meet all other zoning criteria are exempt from width and side yard requirements and may be subdivided and sold as separate units if the common wall built between the units meets tougher building code standards. The same could be done for row houses and townhouses that met stricter building and fire code standards.
If increasing average density is the goal, restricting the size of farmettes, estates and rural subdivisions is another important consideration. One, three and ten acre estates at the edge of town or in rural subdivisions can use four to 40 times more land per unit than similar value houses in the city limits. ISU's recently-released pilot land use inventory shows 40 percent of the farmland use conversions are more than two miles away from the limits of any city or town.
Ames recently approved a goal for increasing density to four housing units per acre. Subtracting the public right of way, this means an average lot size would be about 8,500 square feet. This does not mean that all lots must be the same size. It simply means that developments with higher density must be approved to offset developments with lower density. By setting a goal, the Zoning Commission and Council gain leverage in adjusting new developments.
One approach recommended for discouraging subdivisions in prime agricultural areas is to increase minimum size requirements for subdividing farmland. This approach, however, can sometimes have unintended results. Raising the minimum size requirement from one to ten acres for a residence on land zoned for agriculture reduces the number of 1 acre farmettes created, but it may increase the number of 10-acre farmettes created. Relatively few 10-acre farmettes can offset the farmland saved by eliminating demand for one acre farmettes.
The complementary approach of adding maximum lot size restrictions for increasing density in urban development also has limits. If maximum lot sizes suddenly become too restrictive for consumer tastes at one location, consumers and developers will vote with their feet. From a regional perspective, other developments in the community, rural subdivisions or other communities in commuting distance may currently offer larger lots at lower prices.
Edelman is a professor of economics and an extension public policy specialist at Iowa State University.
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