Before You Build in Seattle, WA: Permit & Rule Checklist (2026)

Under SMC 23.44.014, fences in single-family zones may be up to 6 ft solid in side/rear yards. Above 6 ft, fences must be predominantly open (50%+ open); total max is 8 ft. Front yard fences: max 4 ft in required setbacks. Fence + retaining wall combined max: 9.5 ft.

Seattle enforces the Seattle Residential Code (SRC) Appendix G, which adopts International Residential Code Section AG105 for private residential pool barriers. Pools and spas with water deeper than 24 inches must be enclosed by a barrier at least 48 inches high. Public, semi-public, and apartment/condo pools are regulated separately by Washington WAC 246-260, requiring 60- to 72-inch barriers.

Garage conversions to ADUs are allowed in Seattle under SMC 23.42.022 as part of HB 1337 compliance. Conversion provisions apply in all residential zones. Building permits required from SDCI. Must meet Seattle Building Code and accessibility standards.

Seattle adopted Ordinance 127211 (June 2025) to comply with HB 1337. Up to 2 ADUs allowed per lot by right in all residential zones (SMC 23.42.022). No owner-occupancy requirement. Max ADU size 1,000 sq ft. ADUs cannot be used as STRs. DADUs allowed up to 32 ft in most NR zones.

Carports in Seattle's Neighborhood Residential zones are regulated as parking/garage accessory structures under SMC 23.44.016, with placement controlled by SMC 23.44.014 (yards). They cannot occupy the front 20 feet of a lot or side yards within 5 feet, and the combined footprint counts toward the 35% lot-coverage limit on lots 5,000 sq ft or larger.

Seattle allows tiny houses on permanent foundations as Detached Accessory Dwelling Units (DADUs) under SMC 23.42.022 and SMC 23.44.041, subject to the same code as any DADU. Tiny houses on wheels (THOWs) are treated as recreational vehicles and may not be used as residences in city residential zones. Sanctioned tiny house villages exist only as transitional encampments under SMC 23.42.054.

One-story detached accessory structures (sheds, playhouses) under 200 sq ft do not require a building permit under Washington State Building Code (IRC). Structures in Environmentally Critical Areas require additional ECA review regardless of size. Setback and zoning requirements apply.

Outdoor fire pits and open flames are heavily restricted in Seattle due to the city's general prohibition on open burning. PSCAA burn bans also apply. Chimineas and enclosed fire pits may be subject to city and state air quality rules.

Open burning in Seattle is prohibited except during approved ceremonial events. Puget Sound Clean Air Agency (PSCAA) issues burn bans for King County. Residential outdoor burning is not permitted in Seattle city limits.

Seattle's Tree Protection Code (SMC 25.11, effective July 30, 2023) classifies trees by tier. Tier 2 trees generally cannot be removed except for hazard. Tree removal typically requires SDCI approval. All tree work must be done by a Registered Tree Service Provider (RTSP) since August 2024. Violations: up to 3x tree appraised value.