A Residential Cluster Development, or conservation development, is the grouping of residential properties on a development site in order to use the extra land as open space, recreation or agriculture. It is increasingly becoming popular in subdivision development for its low impact and sustainability appeal. The idea of clustering housing units dates back to early settlements when houses were grouped to form a common area to defend themselves. Today it serves other advantages, including more green/public space, closer community, and an optimal storm water management. Though cluster development has many benefits, it has issues such as outdated zoning, perceptions of personal space and maintenance of common areas.
According to William H. Whyte, the author of “Cluster Development” there are two types of cluster development. Townhouse development and super development. Examples of townhouse development include Morrell Park, Philadelphia, Pennsylvania, Hartshone in Richmond, and Dudley Square in Shreveport. Examples of Super Development include Reston, Virginia, Crofton, Maryland, and Americana Fairfax in Virginia.
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In many ways cluster development has been practiced since the earliest communities — from the medieval village to the New England town. However, it wasn’t formalized as a concept until the onset of suburban sprawl and ubiquity of detached house developments. The idea of a Cluster development was created as the alternative to the ‘conventional subdivision’. The first conscious application of a Cluster development was in Radburn, New Jersey in 1928. Though it was based on English planning and Ebenezer Howard’s Garden Cities movement, it used principles of cluster development. Following Radburn, many other towns in New Jersey applied those principles to their planning notably the ‘village green’ in Hillsborough, NJ and Brunswick Hill in South Brunswick. In the rest of the country the use of cluster development grew in principally in Maryland and Virginia; notably in Reston and American Fairfax County.
Currently cluster development is applied all over the country. There is particularly a strong push for it in the Midwestern states that have had significant problems with large lot suburban sprawl, such as Minnesota, Illinois, Ohio, and Wisconsin.
Cluster Development also known as conservation development is a planning approach that is an alternative to conventional subdivision development. It is a practice of Low Impact Development that groups residential properties in a proposed subdivision closer together in order to utilize the rest of the land for open space, recreation or agriculture. Cluster development differs from a planned unit development (PUD) due the fact that a PUD contains a mix of residential, commercial, industrial, or other uses were as the cluster development primarily focuses on residential area. [1]
The purpose of cluster development is to:
As mention before, the benefits of cluster development as opposed to a convention subdivision include: more preserved land for open/recreational space, a better setting for community building, possible local agriculture production, and an optimal arrangement in storm water management; furthermore cluster development makes more ecological and economical sense.
By clustering residential properties there is less impervious surface and more natural drainage which reduces storm water flooding, and soil erosion. As well, strategic areas in the extra space can be used trap nutrients and suspend runoff.[3] Economical benefits include having fewer roads, sewer/drainage, and electric/gas utility infrastructure to construct. Also higher density means reduced travel time for services as well as the possibility for public transportation, increased bicycle usage, and pedestrianism. This subsequently would mean less petroleum usage, and Co2 emission; as well, there is the possibility of having community-supported agriculture (CSA) which decreases food miles and supports local economy. Higher density also has implications for an increase in recreation and community.
Following World War II, migration from the cities to suburbs became a dominant trend in America. People were acquiring any land they could find; as a result developers attempted to squeeze as many lots as they could on development sites. Communities then developed zoning regulations to limit the number of units and density allowed on a site. Though this zoning protected land for communities and to an extent preserved land from development, it was what ultimately led to the suburban sprawl as we know it today.[4] It is this zoning that cluster development attempts to amend, and is the primary issue it faces.
Most municipalities have established zoning which restricts developers, planning boards and communities to only use this conventional subdivision development. Thus, the practice of traditional development is difficult to change due the set standard, familiarly of the procedure, and the fear of undertaking something new. In response to this, groups such as the American Planning Association have developed a model ordinance that provides the framework for cluster development. This ordinance is not difficult to administratively implement, though politically it is problematic due to conservative resistance.
People’s perception of personal space has a large part to do with this resistance. Many cases people chose to live in suburbs with the intention of having a large lot property; therefore it is hard to convince those individuals to live closer together. Convincing people to accept small lot sizes and higher density living remains one of the biggest obstacles of cluster development. This obstacle can be mostly overcome with proper site design that grants homes unobstructed views and effective private space. As well as educating people about the benefits of having better community and open space can serve as encouragement to change perceptions.
An additional obstacle to cluster development is the difficulty for creating small lot sizes when no municipal sewer system is in place. When septic systems are used, enough land needs to be available on each building lot for a leach field (sometimes land is required for two leach fields, the additional land set aside as a back-up). The amount of land needed is in proportion to the size of the septic system and the soil conditions, which must allow for the percolation of wastewater safely into the ground. In areas where well water is used, additional lot area may be required to sufficiently separate the well from the leach field. This can lead to minimum lot sizes of 1-acre (4,000 m2) or more, making cluster development difficult. However, installing a package wastewater treatment plant (WWTP) for the development (which acts as a small cluster plant, eliminating the need for individual septic tanks) or using biofilters with each septic system obviate the need for larger lot sizes.[5] In addition, providing a package WWTP reduces the diameter and depth of collection sewer lines for the cluster, thus reducing the overall cost of infrastructure.
The final primary issue with cluster development is the issue of dealing with open, recreational, and agricultural space. These areas do serve as benefits in many respects although they are also issues that are required to be dealt with. The maintenance of open and recreational space requires the formation of home owners associations that necessitate fees for taxes, insurance and general upkeep. This would not be necessary under a typical subdivision, though people would have their own maintenance expenses. As to agriculture: people enjoying living next to it until there is a need to apply fertilizer or pesticides. This fact cannot be avoided, though through the proper use of cluster development there can be wider gaps and barriers between agricultural land and residential properties, which would limit exposure to unwanted byproducts.
The model ordinance for cluster development is section 4.7 in the Smart Growth Codes, issued by the American Planning Association. Along with introducing the concept of cluster development, the ordinance outlines the process of application, site planning and implementation.
The primary requisites for application of cluster development are that all principal or accessory uses are allowed and that multifamily dwelling, duplexes, and townhouses are permitted. As well the application of maximal lot coverage, floor area ratios, building height, and parking requirements to the entire site as opposed to the individual lot. Provisions of a cluster development require that the site is at least 2 to 5 acres (20,000 m2) and there is no minimum to lot dimensions; furthermore each house can be no more than 12 feet (3.7 m) from the street with yard that is at least 25 feet (7.6 m). There also needs to be the ability to place more than one principal building on each lot, and lastly no less than 25% of the site is used for open space.
Included in the application, the site plan is required to consist of the street and sidewalk layout, the maximum number and type of dwelling units proposed, and how much area they will occupy, with calculations; as well as the area of parking, open space, and other accessories. To calculate the permitted amount of dwellings, one must measure the gross area of the site in acres and tenths of an acre, then subtract the gross area of the public and private streets and public dedicated improvement; the remainder will be the build able area. Then divide the net build able area by the smallest minimum lot size; round this number to the nearest lower number and the figure will be the maximum number of units.
There are various distinct design features in cluster development notably: the consideration of natural features/topography, smaller lot size, the use of cul-de-sacs, and the use of certain waste/storm water management techniques.
Along with site design, waste/storm water management design features are a principle aspect of cluster development. Through the maximizing of over land water flow and the strategic use of landforms and plants to slow, hold, and treat runoff it is possible to handle the majority of storm water. As well, there many options in dealing with waste water; techniques such as community drain fields, irrigation systems, and package plants can dramatically reduce the cost of infrastructure, and improve the environment.[6]