Seattle Zoning Code & Building Rules
Data version: Q2 2026 · Last updated 2026-05-13
TL;DR. Seattle uses a land use code with Single-Family (SF), Lowrise (LR), Midrise (MR), Highrise (HR), Neighborhood Commercial (NC), and Seattle Mixed (SM) designations managed by SDCI. Washington HB 1110 (2024) now requires middle housing (duplexes, triplexes, fourplexes) in all residential zones. Mandatory Housing Affordability (MHA) requirements apply in upzoned areas. Buildability™ checks your exact zone, HB 1110 eligibility, and MHA obligations.
Seattle zoning districts
SF 5000 (Single-Family): one dwelling per 5,000 sq ft lot, plus ADUs and middle housing under HB 1110. LR1-LR3 (Lowrise): townhomes and small apartments, 30-40 ft height, 0.75-1.0+ FAR. MR (Midrise): mid-rise apartments up to 60-75 ft. HR (Highrise): towers of 240+ ft in urban centers. NC1-NC3 (Neighborhood Commercial): mixed-use with height varying 30-85 ft. SM (Seattle Mixed): highest-density mixed-use in urban villages.
HB 1110 middle housing mandate
Washington HB 1110 (effective 2024) requires Seattle to allow: duplexes on ALL residential lots, fourplexes on lots within 0.25 miles of major transit stops, and sixplexes in some areas. This eliminates single-family-only zoning statewide. For Seattle property owners, this means every SF-zoned lot now has development potential beyond a single house. Buildability™ identifies your HB 1110 eligibility and maximum unit count.
Mandatory Housing Affordability (MHA)
MHA requires developers in upzoned areas to include affordable housing units (5-11% of total units) or pay a fee ($5-$32.75 per sq ft) into the affordable housing fund. MHA applies in urban villages and areas that received height increases. There are 28 urban villages in Seattle — properties inside them typically have higher density allowances but face MHA obligations that affect project economics.
Permit process
Seattle Department of Construction and Inspections (SDCI) handles all permits and land use reviews. Simple residential: 6-12 weeks. Projects requiring design review: 3-6 months. Master Use Permit needed for discretionary decisions. Design Review Board approval required for projects over certain size thresholds in urban villages. Permit fees increased 12% in 2025. SEPA environmental review may apply to larger projects.
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