Seattle ADU Construction Inspections + CO
Inspections is the on-site construction phase. Seattle inspectors check the work at defined milestones (foundation, framing, mechanical/electrical/plumbing, insulation, final) before the next phase can be covered up. The Certificate of Occupancy (or equivalent final approval) closes out the permit.
Last verified 2026-05-15
| Typical timeline | 16–28 weeks |
|---|---|
| Direct city fees | Included in adjacent phase |
| Reviewing department | SDCI |
| Submittal portal | https://cosaccela.seattle.gov/portal/ |
Timeline and fee ranges are project-level averages aggregated from public data and Golden State ADU project history. Authoritative current numbers live in the Seattle published fee schedule and the city's permit portal — verify before budgeting.
What construction inspections + co actually means in Seattle
Inspections run on the city's schedule, not the contractor's. Most ADU projects need foundation, under-slab plumbing, framing, sheathing/shear, rough mechanical/electrical/plumbing, insulation, drywall, and final inspections — plus separate inspections from the local water/sewer utility for side sewer and water service.
Each milestone is a hard gate. If framing does not pass, drywall cannot go up. Some cities also require special inspections (geotech, structural, fire-rated assemblies) performed by a third party at the owner's cost.
When all inspections pass, the city issues a final / Certificate of Occupancy. The ADU is not legal to rent or occupy until that document is in hand.
SEATTLE NOTE
SDCI inspections are scheduled through the Seattle Services Portal as part of the same permit record used for application and review.
Why Seattle construction inspections + co hits the high end
- 01Construction speed and weather (concrete, framing, exterior trades)
- 02Inspector availability — most cities require 24 hours notice via the inspection portal
- 03Number of re-inspections triggered by failed inspections
- 04Coordination with separate utility inspections (side sewer, water service)
- 05Owner-driven scope changes mid-construction (each one typically needs a revision permit)
Where the dollars actually come from
- 01Most inspection fees are collected at issuance
- 02Re-inspection fees apply when an inspection fails or the contractor cancels too late — see the city's fee schedule
- 03Third-party special-inspection fees (geotech, structural, fire-rated) are paid directly to the consultant
Exact dollar amounts vary by project. Use the Seattle fee schedule linked below for the current numbers.
Common homeowner mistakes
Calling a framing inspection before sheathing nail patterns are visible (or after insulation is in) almost always fails.
Separate utility inspections live outside the building permit portal and are easy to forget until they block a milestone.
Renting an ADU before final / CO is a legal and insurance liability and will surface at sale or refinance.
Construction Inspections + CO checklist
These are typical artifacts for an ADU project at this phase in Washington cities. Exact requirements depend on the project and the current Seattle submittal checklist — verify with the city before submitting.
- Approved plans on site, marked-up with field changes
- Inspection card posted, signed off as inspections pass
- Special-inspection reports filed before the related inspection is called
- Side-sewer and water-service inspections coordinated with the utility
- Address number visible from the street before final
- Certificate of Occupancy / final approval in writing before move-in or rental
When to call a pro
Use a contractor who already understands the Seattle inspection sequence — most failed inspections trace back to scheduling order, not to bad construction.
Seattle Construction Inspections + CO questions
How long does Seattle ADU construction inspections + co take?
For an ADU project in Seattle, WA this phase typically runs 16–28 weeks. Complex sites, missing reports, first-time submittals, or busy permit seasons trend toward the upper end. Resubmittals reset the clock for that round. These ranges are project-level averages — verify the current published timeline with Seattle for your specific project.
Go deeper: Read the King County side sewer permits for ADUs: cost & timeline (2026) guide
What does construction inspections + co cost in Seattle?
There is no separate direct city fee for construction inspections + co in Seattle; costs are absorbed in the adjacent application, review, or issuance fees.
Go deeper: Read the King County side sewer permits for ADUs: cost & timeline (2026) guide
Which Seattle department handles construction inspections + co?
SDCI handles this phase; submittals and status live in https://cosaccela.seattle.gov/portal/. See Seattle Department of Construction & Inspections (SDCI): https://www.seattle.gov/sdci/permits/common-projects/accessory-dwelling-units.
Go deeper: Read the Seattle Design Review for ADUs: when it applies (2026) guide
What's the most common reason construction inspections + co stalls in Seattle?
Out-of-sequence inspection calls and missing third-party special-inspection reports are the usual stall causes in Seattle. We pre-screen every submittal against the current Seattle checklist before it goes to the city.
Go deeper: Read the Seattle Design Review for ADUs: when it applies (2026) guide
Do I need a contractor or designer for Seattle construction inspections + co?
Not legally required for owner-applicants, but in Seattle every ADU permit eventually touches building, land use, fire, and public works review tracks. Contractor coordination is what keeps the schedule honest once the permit is in motion.
Go deeper: Read the Seattle Design Review for ADUs: when it applies (2026) guide
How do I check Seattle permit status during construction inspections + co?
Seattle publishes live status inside https://cosaccela.seattle.gov/portal/. The same record carries application data, review comments, fee balances, and (after issuance) inspection results.
Go deeper: Read the Seattle Design Review for ADUs: when it applies (2026) guide
Seattle permit sources we used
Every claim on this page about Seattle permits, fees, portals, or departments traces to an official city or zoning-code source. Numbers in the at-a-glance table come from our project history and public data; verify current values with the city before budgeting.
- Seattle Department of Construction & Inspections (SDCI) · city pageAccessory Dwelling Unit — SDCI
Defines AADU vs DADU in Seattle, lists the permit types required, and links to current standards.
Accessed 2026-06-03
- SDCI · help articleHow Do You Get a Permit?
Seattle's general permit pipeline: research, pre-app, application, intake, review, issuance, inspections.
Accessed 2026-06-03
- City of Seattle · portalSeattle Services Portal
Official submittal portal for SDCI permits, document uploads, and corrections.
Accessed 2026-06-03