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Indicator: Net Residential Density

Data and Data Discussion provided by King County DNRP

Figure 1: Residential Density

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Upstream Indicators

There are currently no published Upstream Indicators.

Downstream Indicators
  •   Land Use --- The data for this indicator was taken from a snapshot study of King County.  
  •   Walkability --- In 2005, King County finished a major study called “Land Use, Transportation, Air Quality and Health” (which led to the current program HealthScape), that measured how specific land use and transportation actions affect air quality, mobility, congestion, and public health. No trend data are yet available.   (view data graph)
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Related Goals

Sustainability Snapshot:

Greater residential density allows for more and better transportation choices, including mass transit, biking, and pedestrian trails. Such density also improves the walkability of neighborhoods and access to services and amenities while decreasing sprawl and the consumption of land. Density depends on both dwelling unit size and household size.

Sustainability Trend:

Residential densities throughout the urban area of King County have increased over the last 10 years.

Data Discussion

The Indicator Defined

Number of residential lots per acre, permitted single family units per acre and permitted multi-family units per acre. King County plans its residential growth under the Washington State Growth Management Act and is required to establish an Urban Growth Boundary. One way to measure if the county is achieving its goals to promote appropriate residential density is by comparing population growth to land consumption rates and by examining how much residential growth is occurring outside of the Urban Growth Boundary.

Data Interpretation/Evaluation

Residential densities throughout the urban area of King County have increased over the last 10 years. In 2004, 599 acres were divided into 3,848 new lots for single family homes. The highest plat densities were achieved in the Sea-Shore subarea (with 7.5 lots per acre) and south King County (with 6.6 lots per acre). Single family permit densities in King County's urban area increased from an average of 3.8 units per acre between 1996 and 2000 to 5.3 units per acre in 2004. Similarly, multifamily permit densities increased from 22 units per acre to 30 units per acre, with the greatest densities achieved in the Sea-Shore subarea (with 60 multifamily units per acre in 2004). (Figure 1)

Washington State’s Growth Management Act (GMA) requires King County to designate an Urban Growth Area (UGA), where future urban growth and development are to occur. Consistent with the GMA, the King County Countywide Planning Policies (CPPs) call for development to occur within the UGA to promote efficient use of land. Housing and employment growth is to be directed first to urban centers, then to areas already urbanized, and lastly to areas requiring major infrastructure improvements. (Figure 3) The Urban Center strategy, whose goal is to attract employment and housing to the county’s urban centers, is an important element of the CPPs.

Between 1996 and 2004, King County’s urban land was consumed at only half the rate of population growth. (Figure 2) While this trend meets the policy goal of using urban land more efficiently, even greater efficiencies will be needed in the future, as the available supply of vacant land in King County continues to diminish.

Meanwhile, not all of the growth has occurred within the Urban Growth Area. Seattle-area jurisdictions authorized 46,000 residences outside the urban growth boundary from 1991 through 2001. (Figure 1) This kind of residential development threatens goals of compact development and appropriate density.

Data Source and Limitations

Figure 1 data is obtained from the 2002 King County Buildable Lands Report, King County jurisdictions and the Suburban Cities Association.

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    Additional Resources

    • Trend in Achieved Density of Residential Development, King County Benchmarks, Land Use, 2008
      Monitoring changes in residential densities provides an opportunity to measure how efficiently our urban land is being utilized. Comparing achieved to planned densities is very useful at the jurisdictional level. However, planned densities vary greatly from zone to zone, and from city to city. At the sub-regional and County level it is more useful to compare average densities achieved currently to those achieved in the recent past.within each subarea throughout the county. From 2001 to 2005, nearly 26,000 units of new single-family development were permitted or finaled in the Urban Growth Area (UGA), an increase of 33% in permit activity.UGA-wide, over 25,000 multifamily units were permitted with an overall density of 38.0 DUs per net acre in the recent 5-year review period.