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, with 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. It is 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
Seattle ADU permit questions
- Do I need a permit to build an ADU in Seattle?
- Yes. An accessory dwelling unit (ADU) in Seattle requires a building permit. ArchPermit tracks 14 cited requirements for this jurisdiction (5 required, the rest conditional). Always confirm the exact forms, fees, and code edition with the local permitting authority that issues the permit.
- What does an ADU permit package require in Seattle?
- Core required items include: Building & Land Use Pre-Application (Seattle Services Portal); Energy Code Calculations / Forms; Floor Plans (main house + ADU/DADU); King County Residential Sewer Use Certification; Site Plan. Each requirement links to its authoritative source, and nothing is permit-ready until an independent licensed professional reviews and seals it.
- How are ADU permits submitted in Seattle?
- Seattle accepts permit submittals via Seattle Services Portal (Accela). ArchPermit prepares a draft package you can submit there after a licensed architect reviews and seals it.