What is the Seattle Critical Areas Ordinance, and does it affect my lot?

SMC Title 25, Chapter 25.09 (Environmentally Critical Areas) governs development on Seattle parcels that contain or sit adjacent to steep slopes, landslide-prone soils, liquefaction-prone soils, peat-settlement-prone soils, wetlands, riparian corridors, fish-and-wildlife habitat conservation areas, and abandoned-coal-mine zones. The ordinance was first adopted under Washington's Growth Management Act in 1990 and last comprehensively updated in 2017, with an ongoing periodic review under RCW 36.70A.130.

Magnolia, Queen Anne, West Seattle (especially the Admiral and Genesee districts), the Madrona-Leschi corridor along Lake Washington, and the Phinney-Greenwood ridge carry significant exposure. The mapped categories that matter most for residential remodels are steep slopes (over 40-percent grade), landslide-prone areas (Class 1 to 4 with Class 4 being highest hazard), and liquefaction zones (concentrated near Sodo, the Duwamish floodplain, and reclaimed Lake Union shoreline).

When a Critical Areas review is triggered, the typical SDCI requirement stack includes a geotechnical report sealed by a licensed Washington PE specializing in slope stability, an arborist report identifying exceptional trees and root protection zones, a wetland delineation if any flagged hydric soil is within 100 feet, and a buffer-and-setback site plan reflecting the underlying overlay. For steep-slope and landslide hazard areas, SMC 25.09.180 imposes development setbacks measured from the top, toe, and side of any slope feature, often 50 feet or 1.5 times slope height, whichever is greater, and limits impervious surface to 35 percent of the developable area.

Schedule impact runs 4 to 16 weeks of additional review on top of the standard SDCI clock. The high end attaches when the project requires a Reasonable Use Exception (SMC 25.09.280), the safety valve that allows otherwise non-conforming development if no economic use is otherwise possible. RUE adjudication adds 12 to 24 weeks and typically requires Council notification.

The pre-design move that pays back five-fold: pull the SDCI Property Report and the GIS Critical Areas overlay before lot purchase or design kickoff. A West Seattle lot that mapped clean in 2000 may now sit inside an updated landslide hazard polygon, and discovery at framing-permit stage is the single most common cause of six-figure scope cuts.