Auburn, WA Building Setbacks & Zoning: Lot Coverage Limits (2026)
Key Facts
- RC zone cap
- 25% impervious area
- R-1 zone cap
- 50% impervious area
- R-4 / R-NM cap
- 90% impervious area (highest)
- R-F zone cap
- 75% impervious area
- Variance limit
- Max 25% deviation, ACC 18.31.070
Summary
Auburn caps how much of a residential lot can be covered by buildings, driveways and other hard surfaces through a maximum impervious area percentage that varies by zone. The limit runs from a strict 25 percent in the Residential Conservancy zone up to 90 percent in the densest R-4 and R-NM zones.
18.07.030 Development standards. Standard: RC | R-1 | R-2 | R-3 | R-4 | R-NM | R-F... F | Maximum impervious area (%) | 25 | 50 | 75 | 80 | 90 | 90 | 75
Official source re-checked September 8, 2026: no newer edition of the code had been published (publisher’s edition: current through Ordinance 7023, passed July 6, 2026).
Full Breakdown
030's development standards table sets a row F "Maximum impervious area (%)" that applies across Auburn's seven residential zoning designations. The Residential Conservancy (RC) zone, intended for the lowest-density and most environmentally sensitive land, carries the tightest cap at 25 percent impervious coverage. The R-1 zone allows 50 percent, R-2 allows 75 percent, R-3 allows 80 percent, and the higher-density R-4 and R-NM zones each allow up to 90 percent impervious coverage, the highest ratio in the table. The R-F zone is capped at 75 percent.
497 is defined as any hard surface that prevents or retards water infiltration into the soil or increases runoff compared to pre-development conditions, so the cap sweeps in rooftops, driveways, patios, and parking areas, not just building footprints. 50 ACC. 070 caps any such dimensional variance at no more than 25 percent deviation from the quantifiable standard. 31 sets a formula-based lot coverage cap and states that in no case shall lot coverage exceed 60 percent unless otherwise allowed by the title.
Violations & Fines
Exceeding the maximum impervious area percentage for a residential zone without an approved variance is a zoning code violation enforceable by Auburn's Community Development & Public Works Department; the city can withhold or revoke building permits, red-tag work in progress, and require removal or reduction of hard-surface coverage until the parcel conforms to ACC 18.07.030.
Frequently Asked Questions
What is the maximum impervious surface allowed on an R-1 lot in Auburn?
Which Auburn residential zone has the strictest coverage limit?
Can I get a variance to exceed my zone's impervious area cap?
Sources & Official References
Other rules in Auburn
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Lot Coverage Limits in Nearby Cities
How other cities in King County handle lot coverage limits.