ID: AXO-VASH-44 DATE: 2026-01-30 LOCATION: Vashon Heights (East Facing), Vashon Island, WA ZONING_ZONE: RA-5 (Rural Area, 5-acre density)
> QUERY: "Feasibility of a 400 sq ft tiny house on the east side of Vashon Island overlooking West Seattle/Puget Sound."
1. REGULATORY SCAN (THE MUNDANE)
Agent performed a deep-dive on the King County Code (KCC).
Constraint Identified: Under KCC 21A.24.310, "High Hazard" steep slopes (30%+) require a minimum top-of-slope setback of the height of the slope plus 1/3 of that height, or 25 feet, whichever is greater.
The Conflict: Client's desired "cliffside" view sits within the 200' Critical Area Buffer. Standard "Tiny House on Wheels" (THOW) are classified as RVs and cannot be used as permanent residences for more than 60 days under KCC Title 21A.
The Agentic Fix: Pivot to a Permanent Foundation Tiny House (modular/site-built) to qualify as a legal Accessory Dwelling Unit (ADU). Proposed a "Geotechnical Buffer Reduction" by utilizing a pin-pile foundation system to minimize site disturbance and satisfy the Shoreline Master Program (SMP) requirements for the Rural Conservancy designation.
2. PHYSICAL & ENVIRONMENTAL
> SOIL DATA: Vashon Glacial Till (Hard-packed, impermeable) over Recessional Outwash. > STRUCTURAL LOAD: Seismic Design Category D2. Structural design utilizes Helical Piers to bypass the loose weathered top layer and anchor directly into the till, preventing bluff-creep displacement.