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9611 SE 36th Street
Mercer Island, WA 98040
Phone: 206.275.7605
Email: epermittech@mercer. . .

Open to the public:
8:30 AM - 4:00 PM
on Mon, Tue, Thu, & Fri

10:00 AM - 4:00 PM on Wed

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Zoning on the Island

Title 19 of the Mercer Island City Code is the City's Unified Land Development Code. This establishes allowed uses and development standards for each zoning district. This means that there is a list of allowed uses and development standards such as minimum lot size, dimensions, maximum gross floor areas, maximum impervious surface coverage and maximum height.
To See Zoning on a Specific Site: The location and boundaries of the various zones of the city are shown and delineated on the city of Mercer Island Zoning Map.

The City of Mercer Island has four single-family zones, three multi-family zones, four commercial or mixed-use zones, and one public zone, consisting of the following:

Zone Type Symbol Minimum Lot Size ULDC
Single Family R-8.4 Minimum 8,400 SF lots. 19.02
Single Family R-9.6 Minimum 9,600 SF lots. 19.02
Single Family R-12 Minimum 12,000 SF lots. 19.02
Single Family R-15 Minimum 15,000 SF lots. 19.02
Multi-Family, Limited MF-2L The maximum allowed density is 26 units per acre. 19.03
Multi-Family MF-2 The maximum allowed density is 38 units per acre. 19.03
Multi-Family MF-3 The maximum allowed density is 26 units per acre. 19.03
Business B No minimum lot size. 19.04.050
Planned Business PBZ No minimum lot size for non-residential uses; the average parcel size of residential lots shall be 7,200 SF. 19.04.010
Commercial Offices C-O No minimum lot size. 19.04.020
Public Institution P No minimum lot size. 19.05
Town Center TC No minimum lot size. 19.11

The single-family residential zoning districts allow specified uses and lot development. The minimum lot development standards for the single-family residential zoning districts are summarized in the following table:

Zoning Districts Minimum Lot Size1 Minimum Lot Width Minimum Lot Depth
R-8.4 8,400 SF 60 feet 80 feet
R-9.6 9,600 SF 75 feet 80 feet
R-12 12,000 SF 75 feet 80 feet
R-15 15,000 SF 90 feet 80 feet

(1 The shorelands part of any lot and any area of the lot that is part of a vehicular access easement shall be excluded in determining whether a lot complies with the lot's minimum area requirements.)

The following standards apply to all single family zoned property R-8.4, R-9.6, R-12, and R-15:

Minimum Front Yard Setbacks Minimum Rear Yard Setbacks Minimum Side Yard Setbacks Minimum Setback From Public Rights-of-ways and vehicular access easements Maximum Building Height2 Maximum Gross Floor Area3
20 feet 25 feet Lots with a width of 90 feet or less, the side yard setback must sum to 15 feet; provided that no side yard shall be less than 5 feet.  Lots with a width of more than 90 feet, the side yard setbacks must sum to 17% of the lot width; provided that no side yard shall be less than 33% of the required side yard width. 10 feet 30 feet 40% of net lot area.

(2 See Code for how height is calculated.)
(3 See Code for how Gross Floor Area is calculated.)

Examples of how these Codes are calculated can be found in the Site Development Worksheet.

The total amount of impervious surface permitted on a residential lot is governed by the lot slope.

Lot Slope1 Hardscape Lot Coverage
(Buildings & driving surfaces)
Less than 15% 9%
15 less than 30% 9%
30-50% 9%
Greater than 50% slope 9%
(1Lot Slope is calculated by subtracting the lowest elevation on a lot from the highest elevation, and dividing the resulting number by the shortest horizontal distance between these two elevation points.)


Important Note:
This information is summarized from Title 19 of the Mercer Island City Code, "Unified Land Development Code" and is provided for quick reference only. To determine exact requirements, and for other development regulations affecting a parcel or lot, Title 19 should be consulted.


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