SeaTac grading and drainage rules
SeaTac’s clearing and grading permit page lists 7,000 square feet or more of land-disturbing activity as a trigger, along with 50 cubic yards or more of cut or fill, 2,000 square feet of new or replaced impervious surface, and cutting more than 4 feet in vertical depth while filling 3 feet. Other triggers include a project next to a flood hazard area, erosion hazard area, steep slope, landslide, or seismic hazard area, or one in a critical drainage area under the King County manual. Single-family homes, additions, duplexes, and accessory dwelling units skip a separate clearing and grading permit when equivalent plans go in with a building permit.
Stormwater runs on the King County manual. SMC 12.10.010 adopts the 2021 King County Surface Water Design Manual with the City of SeaTac addendum, in compliance with the 2019 Western Washington NPDES Phase II Municipal Stormwater Permit. Sensitive areas and their buffers are regulated under SMC Title 15, where Chapter 15.700 covers critical areas, so a project in a sensitive area or its buffer triggers the clearing and grading permit.
Nearby, we also build in Burien, Tukwila, Des Moines, and Kent, and we serve the rest of western Washington.