King County, WA Building Setbacks & Zoning: Lot Coverage Limits (2026)
Key Facts
- Governing section
- K.C.C. § 21A.09H.030
- R-4 zone max impervious
- 55% of lot
- R-48 zone max impervious
- 90% of lot
- Scope
- Unincorporated urban area only
- Exceeding the cap
- Requires conditional use permit
Summary
Unincorporated King County caps impervious surface, pavement, roofs, decks, by zone under Code § 21A.09H.030: 55% in R-4, 70% in R-6, 75% in R-8, and up to 90% in R-48, measured per lot.
The impervious surface maximum applies to each individual lot. Impervious surface does not include access easements serving neighboring property and driveways to the extent that they extend beyond the street setback due to location within an access panhandle or due to the application of King County Code requirements to locate features over which the applicant does not have control.
Full Breakdown
King County Code § 21A.09H.030 sets the maximum impervious surface percentage, the share of a lot covered by roofs, driveways, patios and other hard surfaces, for residential zones in unincorporated King County outside Seattle, Bellevue, Kent, Renton, and the county's other incorporated cities, which enforce their own codes. The cap ranges from 55% in the R-4 zone to 90% in R-48; North Highline and Skyway-West Hill use nearly identical figures under their own subarea sections. Turf, natural vegetation and stormwater facilities don't count toward the limit, and a lot can only exceed its cap with an approved conditional use permit.
Violations & Fines
Impervious surface is verified during King County building and grading permit review; exceeding the zone's cap without an approved conditional use permit blocks permit issuance and can trigger a code-compliance enforcement case for unpermitted hard surface.
Frequently Asked Questions
Does this apply inside Seattle or Bellevue?
What counts as impervious surface?
Can I exceed my zone's impervious cap?
Sources & Official References
Other rules in King County
Compare King County to another location·View the Washington building setbacks & zoning overview
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