Seattle ADU permit requirements
Last reviewed: June 22, 2026
Quick answer
Permitting an accessory dwelling unit (ADU) in Seattle, Washington means pulling a building permit from the local authority that issues it. ArchPermit tracks 14 source-cited requirements (5 required, the rest conditional) for this jurisdiction. Submittals go through Seattle Services Portal (Accela). These requirements were last reviewed June 22, 2026; confirm the exact forms and fees with the local permitting authority.
A source-cited checklist of what an ADU (accessory dwelling unit) permit package needs in City of Seattle. Every item links to its authoritative source; items that vary are flagged to confirm locally.
All ADU/DADU permits are applied for online via the Seattle Services Portal; AADUs and DADUs always require plan review (never a Subject-to-Field-Inspection permit). Review is ministerial — no public comment period and no appeal to the Hearing Examiner or City Council. The July 2019 ordinance removed the owner-occupancy and off-street-parking requirements and allows up to two ADUs per lot. An expedited pre-approved standard-plan track exists for DADUs in Neighborhood Residential zones (NR-1/-2/-3) with no critical areas and under 750 sf of ground disturbance.
- Building & Land Use Pre-Application (Seattle Services Portal)required
Initial online application that establishes the record number; you upload a PDF site plan to start.
source · reviewed 2026-06-22 - Energy Code Calculations / Formsrequired
Calculations demonstrating Seattle Energy Code compliance; conversions of existing structures must fully comply.
source · reviewed 2026-06-22 - Floor Plans (main house + ADU/DADU)required
Detailed floor plans for both the primary dwelling and the accessory unit; basic plans of the existing dwelling are required even when unaltered.
source · reviewed 2026-06-22 - King County Residential Sewer Use Certificationrequired
Form acknowledging the King County sewer capacity charge; SDCI reports all ADU permits to King County.
source · reviewed 2026-06-22 - Site Planrequired
Scaled drawing showing lot size/shape and the size, shape, and location of existing buildings, the proposed ADU/DADU, driveways, trees, and (for a DADU) a pedestrian path from the right-of-way.
source · reviewed 2026-06-22 - Approved Standard Plan Set (pre-approved DADU track)conditional
For the expedited track, the plan set must include the pre-approved standard plans plus a valid Standard Plan number. Limited to NR-1/-2/-3, no critical areas, under 750 sf of ground disturbance.
source · reviewed 2026-06-22 - Construction Stormwater Control & Soil Amendment Planconditional
Covers erosion/sediment control, pollution prevention, and construction vehicle access during construction.
source · reviewed 2026-06-22 - Environmentally Critical Areas (ECA) Exemptionconditional
Required when working within a steep-slope ECA or its 15-ft buffer; approved exemption plans/reports must be in the plan set.
source · reviewed 2026-06-22 - Exterior Elevation Drawingsconditional
Required when building a new structure or making changes to the building envelope.
source · reviewed 2026-06-22 - Geotechnical Reportconditional
Required for steep-slope, slide-prone, liquefaction, landfill, or peat-settlement-prone sites; waivable by modification request.
source · reviewed 2026-06-22 - Separate Electrical Permitconditional
Electrical work generally needs a separate permit, usually applied for by the electrical contractor — a parallel required permit, not part of the building submittal.
source · reviewed 2026-06-22 - Standard Drainage & Waste Control Planconditional
Required for projects creating less than 5,000 sf of new/replaced impervious surface; a standardized plan is available for the pre-approved DADU track.
source · reviewed 2026-06-22 - Structural Plans (framing, foundation, sections)conditional
Required when building a new structure or an addition.
source · reviewed 2026-06-22 - Topographic Surveyconditional
Required for sites with a steep slope or known/potential slide area (environmentally critical areas); waivable by modification request.
source · reviewed 2026-06-22