Island County, WA Building Setbacks & Zoning: Lot Coverage Limits (2026)
Key Facts
- R Zone impervious cap, 5 ac or less
- 25% of site area
- R Zone impervious cap, over 5 ac
- 10% of site area
- R Zone max building coverage
- 5% (parcels 5+ acres)
- Rural Center max building coverage
- 80%
- CGV Zone max building coverage
- 50%, plus green roof bonus
Summary
In the Rural (R) Zone across unincorporated Island County, impervious surface is capped at 25 percent of a parcel five acres or smaller, dropping to 10 percent above that, and total building coverage tops out at 5 percent of gross site area, under Island County Code section 17.03.180.S.1.
S.Site coverage and setbacks.1.Site coverage. Lot or parcel site coverage is established by a ratio percentage based on the gross site area of the property. Specific coverage ratios are as follows: ... All Residential uses in the R Zone including Accessory Residential Uses Rural PRD Rural Center Uses Rural Village Uses Camano Gateway Village Uses All NR or Institutional Uses in the R, RA, RF, CA Zones
a. Maximum Impervious Surface Ratio (% of Gross Site Area) 25-50%* 80% 70% 20% above total Building Coverage 25% for parcels 5 acres or less in size. 10% for parcels greater than 5 acres in size ... ... c. Maximum Building Coverage of Gross Site Area 5% for parcels 5 acres or larger in size N/A 80% 50% 50% 10%
Full Breakdown
Island County's dimensional standards tie lot coverage to a Site Coverage Ratios table in section 17.03.180.S.1, applied by zone and use category. For a residential use in the Rural (R) Zone, including its accessory residential uses, the maximum impervious surface ratio is 25 percent of gross site area on a parcel of five acres or less, dropping to 10 percent for parcels larger than five acres, reflecting the zone's five-acre minimum lot size and one-dwelling-per-five-acres base density. The same table caps total building coverage on R-Zone residential parcels at just 5 percent of gross site area on parcels five acres or larger.
Non-residential and institutional uses on land zoned R, RA, RF, or CA get a different, more generous allowance: up to 10 percent maximum building coverage. Denser designations fare differently still. A Planned Residential Development using density bonuses is capped at 25 to 50 percent impervious surface and 30 to 75 percent minimum open space, while the Rural Center and Rural Village zones allow up to 80 percent and 70 percent maximum building coverage, respectively, and the Camano Gateway Village (CGV) Zone caps building coverage at 50 percent, though CGV projects that install a green roof can add a matching percentage increase in coverage tied to the size of the green roof, calculated square foot for square foot at a 25 percent multiplier under section 17.03.180.S.1.2.a.
Violations & Fines
Exceeding the maximum impervious surface or building coverage ratio for the applicable zone in section 17.03.180.S.1 is a zoning code violation, handled through the county's standard citizen complaint and enforcement process under sections 17.03.250 through .260, and can block issuance or final approval of the building or land use permit until the site plan is revised to comply.
Frequently Asked Questions
How much of my Rural Zone lot can I cover with impervious surface?
What is the total building coverage limit in the Rural Zone?
Do commercial or institutional properties get a bigger coverage allowance?
Sources & Official References
Other rules in Island County
Compare Island County to another location·View the Washington building setbacks & zoning overview
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