Mercer Island residential zoning
Mercer Island residential zoning and setbacks by zone
Mercer Island's base residential zones share several standards, but side yards depend on lot width and lot coverage depends on slope. Shoreline, critical areas, access easements, and net-lot-area exclusions can materially reduce the initial screen.
On this page4 sections
Official starting point: Mercer Island zoning overview. Verify the parcel zone, current code, and every applicable footnote before fixing the design.
Mercer Island residential base-zone table
| Zone | Minimum lot | Width / depth | Front | Rear | Side yards | Height | Gross floor area |
|---|---|---|---|---|---|---|---|
| R-8.4 | 8,400 sq ft | 60 ft / 80 ft | 20 ft | 25 ft | 15 ft combined up to 90 ft wide; width and façade-height formulas can require more | 30 ft | Lesser of 40% of net lot or 5,000 sq ft |
| R-9.6 | 9,600 sq ft | 75 ft / 80 ft | 20 ft | 25 ft | 15 ft combined up to 90 ft wide; width and façade-height formulas can require more | 30 ft | Lesser of 40% of net lot or 8,000 sq ft |
| R-12 | 12,000 sq ft | 75 ft / 80 ft | 20 ft | 25 ft | 15 ft combined up to 90 ft wide; width and façade-height formulas can require more | 30 ft | Lesser of 40% of net lot or 10,000 sq ft |
| R-15 | 15,000 sq ft | 90 ft / 80 ft | 20 ft | 25 ft | 15 ft combined up to 90 ft wide; width and façade-height formulas can require more | 30 ft | Lesser of 40% of net lot or 12,000 sq ft |
Other rules to check
Other rules that can change the answer
These items link to the city rules behind the guide. They are useful starting points, but they do not replace a property-specific review or a search for private covenants and easements.
| Topic | What it means | Official source |
|---|---|---|
| FAR / GFA | Residential GFA is the lesser of 40% of net lot area or the zone cap: 5,000 sq ft in R-8.4, 8,000 in R-9.6, 10,000 in R-12, and 12,000 in R-15. Garages and covered parking count; qualifying below-grade area can be excluded only with a surveyed design. | Mercer Island residential standards ↗ |
| Setbacks | Front 20 ft, rear 25 ft. Side yards are 15 ft combined with a 5-ft minimum through 90-ft lot width, then 17% combined with each side at least 33% of that total. A side also increases to 7.5 or 10 ft when the adjoining façade crosses the code's height thresholds. | MICC 19.02 ↗ |
| Lot coverage | Maximum lot coverage steps down with average slope: 40% below 15%, 35% from 15% to under 30%, 30% from 30% to 50%, and 20% above 50%. | Mercer Island residential standards ↗ |
| Impervious / hardscape | The residential table separately limits hardscape to 9% of net lot area. Stormwater, shoreline, and critical-area rules can add further constraints. | Mercer Island residential standards ↗ |
| Height | A house must satisfy both the 30-ft average-building-elevation roof limit and the 30-ft downhill exterior-wall/façade limit. | MICC 19.02 ↗ |
| Trees | A tree permit is almost always required. Development review under MICC 19.10 includes at least 30% large-tree retention and priority protection for qualifying exceptional trees. | Mercer Island tree permits ↗ |
| Existing private views | No general citywide private-building-view right was identified in the reviewed residential code. Check recorded view easements, covenants, and shoreline-specific standards. | Mercer Island residential standards ↗ |
| Wetlands, slopes, and critical areas | Mercer Island publishes residential gross-floor-area, hardscape, and lot-coverage limits using net lot area. A public tax-parcel area is not a reliable final denominator when access, critical-area, or other code deductions need to be resolved on a survey. Wetlands, watercourses, erosion hazards, steep slopes, potential-slide areas, and their regulated areas can require critical-area review and professional reports. The slope-based coverage percentage does not establish that the resulting square footage can be safely placed on the site. | Mercer Island environmental review ↗ |
Property-specific checks
What can change the table
- For a lot over 90 feet wide, combined side yards equal 17% of lot width. Each side must be at least 33% of the combined requirement. A side also increases to 7.5 or 10 feet when the adjoining façade crosses the code's height thresholds.
- Maximum lot coverage generally steps down with average slope: 40% below 15%, 35% from 15% to under 30%, 30% from 30% to 50%, and 20% over 50%.
- Mercer Island includes garages and covered parking in residential gross floor area. The feasibility study counts the full assumed garage; a surveyed design may establish that a qualifying below-grade portion is excluded.
- Hardscape is a separate 9% net-lot-area allowance. Gross floor area is the lesser of 40% of net lot area or the zone cap shown in the table.
- A structure generally must stay 10 feet from a public right of way or vehicular access easement. Shoreline and critical-area rules can require more.
How to use this guide
How to use the zoning table for a real property
- 1
Find the parcel on the city's current zoning map and copy the complete zone name.
- 2
Read the full row, table footnotes, and definitions. Do not use only the front setback.
- 3
Check corner-lot yards, access easements, critical areas, shorelines, trees, overlays, and recorded restrictions.
- 4
Use a boundary and topographic survey to place the setbacks against the actual lot.
- 5
Have the city or project team confirm any uncertainty before the design is fixed.
Official resources