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You are here:   Home → Built Environment → Median House Size of New Construction
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Indicator: Median House Size of New Construction

Data and Data Discussion provided by Sustainable Seattle

Figure 3: House Size Distribution within Cities with Most Built Homes in King County

Figure 1: Changing Average Single-Family House Size in King County, WA

Figure 2: Divergent House Size Trend in King County

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Upstream Indicators

There are currently no published Upstream Indicators.

Downstream Indicators
  •   Carbon Footprint --- Since 2004, the state's and King County's emissions have been on the rise. In particular, transportation related GHG emissions and total energy use in King County continue to rise.  (view data graph)
  •   Housing Affordability by City --- Homes prices have increased at a greater rate than incomes over the last two decades, making home ownership less affordable. However, rents have increased at a slower rate, generally in line with median household incomes.  (view data graph)
  •   Urbanization and Impervious Surface Changes --- The number of acres of urban land, clear-cut, and regenerating forest have increased in King County since 1986. Acres of grass and deciduous, mixed and coniferous forest have decreased. Acres of rural forests and privately owned working forests have declined in recent years  (view data graph)
  •   Housing AND Transportation Costs as a Percentage of Budget --- There is no on-going reporting for this indicator broken down for King County or the Central Puget Sound, though there are multiple data sources showing that the costs of transportation and housing are going up in the region. Recent hikes in gas prices indicate that these costs will continue to escalate.  (view data graph)
  •   Housing Affordability Gap --- The ratio of median income sales price to median household incomes has increased in all four Central Puget Sound counties from 1995 to 2007. (2) Median income levels generally have kept better pace with increases in average rents from 2000 to 2006. (1)  (view data graph)
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Sustainability Snapshot:

National and local trends show we're building and buying increasingly larger homes. While green built homes help reduce environmental impacts, generally speaking, the trend towards larger houses signals more resource consumption, both for home construction (wood, metal, land) and operation (electricity, natural gas, water). Larger houses also push up the cost of land, thereby contributing to the shortage of affordable housing.

Sustainability Trend:

Median house size of new construction has increased over the past decade with consequence for climate change, resource consumption and housing affordability.

Data Discussion

The Indicator Defined

Median size of new residential construction in King County

Data Interpretation/Evaluation

Overall, median house size has increased in King County by 273 square feet or 11 percent from 1997-2006. This increase during the study period is consistent with a relatively steady increase in house size over the last 50 years (Figure 1). This also reflects well with national trends of house size increase.

When this data is disaggregated into four or more bedrooms, three bedrooms, and homes with two bedrooms or less, major differences emerge. The four or more bedrooms homes are increasing in size at a much faster rate during the study period than homes with two bedrooms or less. The former have increased 13 percent from 2,910 to 3,302 square feet where the latter have decreased ten percent in average square footage from 1,645 to 1,482 (Figure 2).

Another aspect to consider is how the number of homes has changed over time. The overall number of homes built increased on average by almost 50 percent during the study period.  The largest increase was seen in the number of four or more bedroom homes, which increased by 61 percent.  Homes with two bedrooms or less increased in number by 27 percent and the number of three bedroom homes increased slightly by four percent. 

Low number of homes built in a particular city skewed the data when there were outliers in house size. The city of Medina, for example, had a single 9000 square foot two bedroom house. This skewed the average total for the six two bedroom or less classification during the study period.  Seattle also stands out as a large city with a high number of homes with two bedrooms or less. This is due largely to the townhouse phenomenon that has resulted in many new two bedroom Seattle homes in the last ten years.

House size is important when considering environmental impacts, but total numbers of large homes provide a better picture of the overall built square footage.  The largest numbers of homes were built in unincorporated King County and Seattle. Nearly half of all of all homes built during the study period were in these two areas. These two areas account for over 60 percent or 35 thousand of all homes built in King County during the study period.

Some of the cities with the biggest homes only built a small number them. When the overall square footage is analyzed, all of the homes built in the five cities above with averages over 5000 square feet amount to less than two percent of the total square footage built in the five cities with the most number of homes built. Therefore, the largest homes may not necessarily contribute the greatest impact on the environment or carbon emissions as opposed to the  average increase in a greater number of homes (Figure 3).

Data Source and Limitations

The data and data discussion for this indicator was excerpted from: Christian Rusby, Growing Homes: Increasing House Size in King County, 1997-2006, Summer 2008. Master’s of Urban Planning Professional Project, University of Washington. 

For this research, King County Assessor’s tax data is used for single-family detached residences built from 1997 to 2006. This timeframe of the mid-nineties through 2006 has been identified in housing literature as a relative ‘boom’ period for housing for both growths in size and number of homes. The time period for this research was selected to reflect the adoption of the Comprehensive Plan, Urban Growth Boundary, and the most recent house size changesin King County.

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