The third type of housing figure contained in the Comprehensive Plan is a local housing forecast. Table 4 contains a housing unit and population forecast for 2010 through 2030 conducted by the Puget Sound Regional Council (PSRC), using a parcel-based land use model called UrbanSim, based on existing zoning and land use designations.
PSRC anticipates an increase in housing units at an average annual growth rate of approximately 0.25% between 2010 and 2040. This represents an increase of approximately 453 housing units and 1,495 people over 30 years.
The Housing Unit and Population forecasts are informed estimates based on several factors such as growth trends for new single family and accessory dwelling units over the last several years, Puget Sound Regional Council forecasts of future household size, transportation systems and demand modeling, and real estate market fluctuations.
Given the uncertainty of future market forces, periodic reviews of housing and population forecasts should be made to evaluate the future growth assumptions. Adjustments to this forecast will also be necessary if the projections on household size and population growth vary significantly from those forecasted. Planning staff predict that PSRC’s multifamily unit growth estimates for the period through 2030 are likely to be surpassed as early as 2020. This prediction is based on the established pattern of larger, mixed use developments adding 100-200 units at a time to the City’s multifamily housing supply and projects that are now in the development pipeline. The City will continue to monitor housing unit, population growth and market trends, and adjust land use, transportation, and capital facilities planning as necessary prior to the next major Comprehensive Plan update in 2023.