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Typical American Subdivisions

Special Studies, October 3, 2016
By Paul Emrath, Ph.D. and Carmel Ford

Economics and Housing Policy
National Association of Home Builders

Report available to the public as a courtesy of HousingEconomics.com

In May of 2016, the National Association of Home Builders (NAHB) conducted its second survey of development projects across the U.S. Results from the 2016 survey show that the median size of a subdivision is 25 total acres, and the median number of housing units in a subdivision is 50. The results from the previous (2014) survey were not drastically different, although the median number of housing units in a subdivision was somewhat higher in the earlier survey (Figure 1).

Figure 1. 2014 and 2016 NAHB Development Project Surveys Compared

A question added to the 2016 survey asked about how many acres in a subdivision are dedicated specifically to housing. From this it is possible to calculate a measure of net residential density, or how many housing units are actually placed on an acre in practice. In 2016, the median net residential density was 4.0 housing units per acre—3.2 for subdivisions consisting exclusively of single-family detached homes.

In both the 2014 and 2016 surveys, roughly 70 percent of the subdivisions contained only single-family detached housing. Median acreage of the single-family only subdivisions is about the same as for all residential subdivisions, but the median number of housing units for single-family only subdivisions is somewhat lower. Retail or other commercial space is less common in subdivisions that contain only single-family detached homes. After briefly describing the 2016 survey, the rest of this article discusses the characteristics of development projects of different types. For a description of the 2014 survey, see the previous Special Study

The 2016 NAHB Survey

In federal housing surveys, data is usually collected at the level of an individual housing unit. For multifamily housing, the government collects some data on new buildings. There is also a recent effort by HUD and the Census Bureau to collect more comprehensive multifamily data by property. But for single-family housing, data have really never been available at the level of a subdivision. Private vendors may collect some relevant information, but understandably undertake an effort only when they believe it will be profitable, so the information tends to be available only in select areas, for certain types of projects, and often at considerable cost.

To help fill this gap, in May of 2016, NAHB’s Economics and Housing Policy group conducted a survey to collect information about residential development projects across the US. The survey was sent electronically to 1,490 NAHB members whose primary business activity is land development. A total of 121 responded (an 8 percent response rate). The survey asked developers to provide information for up to three projects that they currently have underway, or have recently completed. Thirty-seven developers provided data on one project, 29 provided data on two, and 55 provided data on three projects.

In the U.S., most jurisdictions require that development projects have a minimum number of housing units to classify it as a subdivision. Although practices vary, a common threshold is 4 housing units. Only a handful of the projects captured in the 2016 contained fewer than 4 housing units. After deleting these, the sample contained a total of 254 4-plus unit development projects. This article presents summary statistics for these projects and refers to them as subdivisions.

Among other things, the 2016 survey provided developers with a brief summary of the official definition of a metropolitan area (a densely settled urban area and surrounding counties tied to the urban area by frequent commuting) and asked if each development was inside or outside a metro area. Overall, the developers indicated that three-fourths of their subdivisions were in metro areas.

The survey also collected information on the type of housing built in the subdivision: single-family detached, townhome or multifamily. For purposes of this report, townhome and multifamily subdivisions are grouped together in an “attached” category. Seventy-two percent of the subdivisions in the 2016 survey sample are single-family detached, 13 percent are attached, and 15 percent are “mixed” (containing a combination of single-family detached and attached housing).

Subdivision Size

In terms of total acreage, the size of subdivisions varies widely. At the top end, some projects span many square miles, and the averages tend to be driven strongly by these relatively few extreme cases. For example, the average size of a subdivision in survey sample is 244 acres, compared to the median of only 25. Because the median better reflects projects being developed by a large share of NAHB members, this report generally uses medians to describe “typical” subdivisions. The detailed tables (available under additional resources) shows the averages as well as medians.

As Figure 2 shows, the median number of acres for subdivisions in metro areas is 29 acres, compared to 20 acres for those located outside of metro areas. These findings stand in contrast to the 2014 results: the non-metro median acreage was 40 that year, which was larger than the 20 acres for projects in metro areas. The figure also shows that the median size of subdivisions with a mix of single-family detached and attached housing is significantly larger than that for single-family detached only, and attached-only projects.

Figure 2. Median Number of Acres by Type of Subdivision

As mentioned above, the 2016 survey also asked developers about how many of the acres in a subdivision are dedicated to housing. Sometimes, this can be the same as the subdivision’s total acreage—as might be expected when, for example, the development consists of a single residential city block. But for nearly 80 percent of the subdivisions in the sample, there was a (frequently substantial) difference between the size of the subdivision and the area dedicated to housing. Developers often are required by their local jurisdictions to set aside land for environmental reasons, parks, open space, etc. Some developments are also mixed-use, with space dedicated to commercial as well as residential use (see below).

Overall, the median number of acres dedicated to housing units for subdivisions in the survey is 17. The number of acres dedicated to housing units is slightly higher in metro areas at 19 acres, compared to 12 acres outside of metros. Mixed housing subdivisions have a median of 55 acres dedicated to housing, compared to 17 acres for single-family detached only, and 3 acres for attached-only subdivisions (Figure 3).

Figure 3. Median Number of Acres Dedicated to Housing Units by Type of Subdivision

Number of Homes

The size of a subdivision can also be measured in terms of the number of homes built in it. As Figure 1 showed, the median number of housing units in subdivisions in the 2016 survey is 50. Metro and non-metro area subdivisions contain roughly the same number of housing units. The median number of housing units in subdivisions inside metro areas is 50, compared to 46 for development outside of metro areas. Mixed housing subdivisions, which are the largest in terms of total acreage, also contain the most housing units. The median in mixed housing developments is 314 housing units, compared to a median of 65 in attached-only, and 45 in single-family detached only subdivisions (Figure 4).

Figure 4. Median Number of Housing Units by Type of Subdivision

Given the acreage in the subdivision dedicated to housing, and the number of housing units built on those acres, it’s possible to calculate a measure of net residential density. The median net residential density for all subdivisions is 4.0 units per acre. For subdivisions located inside metro areas, the median net residential density is 4.0 units per acre, slightly higher than the 3.8 units per acre for non-metro developments. When looking at the net residential density of subdivisions by type of housing, attached-only subdivisions have the largest median net residential density of 18.8 units per acre, compared to 5.8 units per acre in mixed housing developments, and 3.2 units per acre in single-family detached only (Figure 5).

Figure 5. Median Net Residential Density by Type of Subdivision

For comparison, NAHB tabulation of data from the Survey of Construction (conducted by the U.S. Census Bureau with partial funding from HUD) shows that the median lot size for new single-family detached homes built for sale in 2015 was just under one-fifth of an acre (see the recent NAHB Eye on Housing post). The same post shows how the median lot size been declining over time, and in 2015 was the smallest on record since the Census Bureau began tracking the data.

Mixed-Use Development

Mixed-use is a type of development that blends residential with commercial of other land uses. The NAHB survey collected information specifically about space set aside for retail or other commercial use in the subdivision. Overall, 9 percent of the subdivisions have retail space, and 11 percent have commercial space other than retail.

Inside metro areas, 9 percent of subdivisions include retail space, compared to 8 percent of non-metro area projects. Twenty-seven percent of attached-only developments include retail space, compared to 19 percent of mixed housing and a mere 3 percent of single-family detached only developments.

The share of subdivisions with commercial space other than retail was 10 percent both inside and outside of metro areas. Again, land set aside for commercial uses was much more common in residential development that includes housing other than single-family detached. Twenty-nine percent of the mixed housing developments, and 26 percent of attached only, include commercial space other than retail, compared to a mere 3 percent of single-family detached only developments (Figure 6).

Figure 6. Retail and Other Commercial Space Included by Type of Subdivision

Community Associations

The survey also contained a question on whether there is a HOA, condo, or other type of community association for the development. Results show that 80 percent of the subdivisions have one of these association types.

Inside metro areas, 82 percent of the subdivisions have a HOA/condo/community association, compared to 75 percent outside of metro areas. Eighty-six percent of mixed housing developments have a HOA/condo/community association, compared to 83 percent of single-family detached only, and 58 percent of attached-only developments (Figure 7).

Figure 7. HOA/Condo/Community Association by Type of Subdivision

The likelihood of a project having a HOA/condo/community association increases as the number of housing units increase. Seventy-eight percent of projects with 4 to 49 units have a HOA/condo/community association, compared to 83 percent of projects with 50 or more units (see the detailed tables available under “additional resources”).

For comparison, NAHB tabulation of data from the Survey of Construction shows that 59 percent of new single-family homes started in 2015 were part of a community or homeowner’s association.

As the above discussion has demonstrated, significant differences exist among subdivisions projects depending on where they are located and the type of housing built in them. For convenience, a profile for each of the five major types of subdivisions is compiled and made available in the “additional resources” box that appears at the top of the online version of this article. Also available under “additional resources” are detailed tables with additional information for each type of subdivision and breakdowns by region and housing units in the development, as well as a copy of the questionnaire for the 2016 NAHB survey used to collect the data for this article.

For more information about this item, please contact Paul Emrath at 800-368-5242 x8449 or via email at pemrath@nahb.org.

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