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Single family residential zoning accounts for 88% of the Island’s land use. There are 3,534 acres zoned for single family residential development. This compares to 77 acres in the Town Center zones, 19 acres for Commercial Office zone, and 103 acres in multi-family zones (Table 2). City Hall is located in a Commercial Office zone, while other key civic buildings such as the Post Office and the Main Fire Station are located in the Town Center and City Hall. Many of the remaining public buildings, schools, recreational facilities and places of religious worship are located in residential or public zones.

Table 2. Land Use Zones and Acreage (2014)

ZONE

ACREAGE

Business - B

2.85

Commercial Office - CO

19.45

Multifamily - MF-2

42.03

Multifamily - MF-2L

7.73

Multifamily - MF-3

53.73

Public Institution - P

284.31

Planned Business - PBZ

13.89

Single Family - R-12

77.44

Single Family - R-15

1277.04

Single Family - R-8.4

779.36

Single Family - R-9.6

1399.98

Town Center - TC

77.16

Note: Figures above include adjacent right-of-way.

Approximately 95% of all residential land on Mercer Island is currently developed. Over the last thirty years, most public facilities have been re-constructed, or have planned additions, in sufficient quantities to serve current and projected populations. This category includes schools, parks and recreation facilities, streets and arterials, and fire stations. Future re-investments in these facilities will primarily improve the reliability and function of the community’s “infrastructure” rather than adding significant new capacity. [Refer to the Capital Facilities Element for a more in-depth discussion of public facilities.]

Single family residential zones designate a number of different lot sizes and densities including 8,400 sq. ft., 9,600 sq. ft., 12,000 sq. ft. and 15,000 sq. ft. Of the 3,534 acres in these zones, approximately 145 remain unimproved. Most unimproved lots are small parcels and/or are platted building lots within previously developed neighborhoods. Some additional capacity exists in larger lots which can be subdivided. However, during the planning horizon, the City expects an average of roughly six subdivisions a year, the majority of which will be short plats of four or fewer lots.

The most densely developed neighborhoods are found on the Island’s north end. This includes East Seattle and First Hill as well as neighborhoods immediately north and south of the I-90 corridor and areas along the entire length of Island Crest Way.

The least densely populated neighborhoods are ones with the largest minimum lot size and are designated as Zone R-15 (15,000 sq. ft. minimum lot size). These neighborhoods, generally located along East and West Mercer Way, contain the greatest amount of undeveloped residential land and often contain extremely steep slopes, deep and narrow ravines and small watercourses. Because environmentally sensitive areas often require careful development and engineering techniques, many of these undeveloped lands are difficult and expensive to develop.

Generally, Mercer Island’s oldest neighborhoods are situated on a fairly regular street grid with homes built on comparatively small lots 40 to 60 years ago. Interspersed among the older homes are renovated homes and new homes that are often noticeably larger. Newer developments tend to consist of large homes on steeply pitched, irregular lots, with winding narrow private roads and driveways. Many residential areas of Mercer Island are characterized by large mature tree cover. Preservation of this greenery is an important community value.

Most Mercer Island multi-family housing is located in or on the borders of the Town Center. However, two very large complexes straddle I-90 and are adjacent to single family areas. Shorewood Apartments is an older, stable development of 646 apartment units. It was extensively remodeled in 2000. North of Shorewood and across I-90 is the retirement community of Covenant Shores. This development has a total of 237 living units, ranging from independent living to fully assisted living.

There is one Commercial/Office (CO) zone outside the Town Center. It is located along the south side of the I-90 corridor at East Mercer Way and contains several office buildings, including the Mercer Island City Hall. In the summer of 2004, the regulations in the CO zone were amended to add retirement homes as a permitted use with conditions.

For land use and transportation planning purposes, Mercer Island has not been designated as an Urban Center in the Puget Sound Regional Council’s Vision 2020. As such, Mercer Island will not share in the major growth of the region, but will continue to see new employment and residential development, most of which will be concentrated in the Town Center. Employment will continue to grow slowly and will be significantly oriented towards serving the local residential community. Transit service will focus on connecting the Island to other metropolitan and sub-regional centers via Interstate 90 and the region’s high capacity transit system.