Seattle ADU Permit Guide
Seattle ADU permitting should be treated as a project-planning step, not a paperwork afterthought. The permit path depends on the property, design, scope, and official review.
Start With Official Guidance
Seattle homeowners should begin with SDCI accessory dwelling unit guidance and current permit information. Requirements can change, and a property-specific review may uncover constraints that are not obvious from general online reading.
Official guidance is the source of truth for permits, submittal requirements, and review process details.
Information Often Needed Early
Early ADU planning may involve a site plan, existing conditions, proposed floor plan, exterior scope, utilities, structural information, and details about life-safety, ventilation, plumbing, electrical, and mechanical systems.
Seattle SDCI Tip 103 and ADU guidance can help homeowners understand the type of site-plan information that may be relevant.
Permit Path Depends on Scope
A detached new structure is different from an interior conversion. Structural work, additions, plumbing, electrical, mechanical, and site changes can each affect the review path. Do not assume one neighbor’s permit experience applies to your property.
Contractor and Professional Verification
Washington State L&I provides contractor-registration resources homeowners can use when evaluating contractors. For ADU work, homeowners should be careful about qualification, insurance, communication, and project coordination.
Inspections and Closeout
Permitted work may require inspections at appropriate stages. Inspection timing and requirements depend on the permits and scope. Homeowners should plan for inspection coordination as part of the schedule, not as an afterthought.
Homeowner Checklist
- Review Seattle SDCI ADU guidance before design decisions are finalized.
- Collect existing drawings, surveys, or property documents if available.
- Ask what permits and trade permits may apply to the proposed scope.
- Verify contractor-registration information through Washington L&I resources.
- Do not begin permit-sensitive work based only on assumptions.
Frequently Asked Questions
Do Seattle ADUs require permits?
ADU projects generally involve official review and permits, but the exact requirements depend on scope and property conditions. Use current SDCI guidance for the specific project.
Can I design first and permit later?
Design and permitting should inform each other. A design that ignores site and code requirements may need revisions.
Does SDCI approve every ADU idea?
No approval should be assumed. Official review depends on the property, proposal, completeness of submittals, and applicable requirements.
Should homeowners verify a contractor?
Yes. Washington L&I provides contractor-registration resources. Verification is one part of evaluating a contractor, along with references, communication, scope clarity, and insurance.
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Planning an ADU?
Titan Build Group can help you think through scope, priorities, site conditions, and the information needed before a project-specific conversation.