The Comprehensive Plan contains three types of housing figures: a capacity estimate, a growth target, and a housing and population forecast. Each of these housing numbers serves a different purpose.
As required in a 1997 amendment to the Growth Management Act (RCW 36.70A.215), recent growth and land capacity in King County and associated cities have been reported in the 2014 King County Buildable Lands Report.
The capacity estimate identifies the number of new units that could be accommodated on vacant and redevelopable land under current zoning. The capacity estimate is not a prediction of what will happen, merely an estimate of how many new units the Island could accommodate based on our current zoning code, the number and size of vacant properties, and some standard assumptions about the redevelopment potential of other properties that could accommodate additional development.
According to the 2014 Buildable Lands Report, the City of Mercer Island has the capacity for 2,004 additional housing units on properties designated for residential uses through new development on vacant lands and/or through redevelopment of underutilized lands. Based on zoning and redevelopment assumptions done in 2012 for the Buildable Lands Report, about 614 new housing units could be accommodated in single family zones, 143 new housing units could be accommodated in multifamily zones and 1,247 units could be accommodated in the Town Center.
Redevelopable land in the Town Center was determined based on an analysis of those parcels which currently have an improvement to land value ratio of .5 or less and are not in public or utility ownership. Additionally, townhomes and condominium properties were not considered redevelopable, and only those properties allowing 2.5 residential units or more are included in the analysis. Future assumed densities for this preliminary figure were based on the density of recently permitted projects (2/3 mixed-use, 1/3 commercial only). This methodology used in the 2014 Buildable Land Analysis is a similar methodology used in the 2007 Buildable Lands Report.