Addition permits in City of Seattle: fees, timeline & requirements (2026)
Everything you need to know about pulling a home addition permit in City of Seattle, Washington — when one is required, what it costs, how long review takes, what documents are required, and which inspections you can expect. Cited to Seattle Department of Construction & Inspections (SDCI).
Free lookup, no account needed — your lot polygon, zoning, setbacks and overlays, cited to City of Seattle's source.
When does a home addition need a permit in City of Seattle?
Any additional floor area requires Construction Permit (Addition or Alteration). Plan review required. ECA + lot coverage + setback compliance verified at intake.
How City of Seattle adopted this rule
The threshold comes from the state code (WAC 51.51), which City of Seattle adopts by reference in the provision quoted below.
“Table A for 22.101.010 lists various adopted Seattle editions of construction codes. For each base code that has been adopted by reference, a copy is available in the City Clerk's Office under the listed Clerk File number. Each code consists of the listed portions of the base code, any additional chapters listed as adopted by ordinance, and amendments adopted by ordinance.”Source ↗verified 2026-04-26
Required submittals
- architectural plans
- structural calcs
- WSEC compliance form
- site plan w/ setbacks + lot coverage
- survey if near setback or in ECA
Inspection sequence
- footing
- foundation
- framing
- rough-in (electrical/plumbing/mechanical)
- insulation
- drywall
- final
Contractor specialties needed
general, electrical-01-or-02, plumbing, mechanical
Who can do this work in City of Seattle?
Kolmo Construction is a licensed Washington general contractor — KOLMOL*753JS, active through April 10, 2027, bonded and insured — working throughout City of Seattle and King County. Kolmo prepares the drawings and submittals, files the home addition permit with Seattle Department of Construction & Inspections (SDCI), carries the project through review and inspections, and performs the construction. Call (206) 410-5100 for a City of Seattle home addition quote.
Notes & caveats
Full structural plan review. Lot coverage in NR zones is limited to 50% (SMC 23.44.080.A). Energy code applies to new conditioned space.
Addition permit fee estimate in City of Seattle
Worked example for a $120,000 home addition project (building permit). Your actual fee scales with project valuation.
| Building permit fee | $1,976.5 |
| Plan review | $1,976.5 |
| Technology surcharge | $197.65 |
| WA state surcharge | $6.5 |
| Estimated total | $4,157.15 |
Construction Permit (Addition/Alteration). Pay 75% of plan-review + permit fees at application acceptance. See SDCI 2026 Fee Estimator. Computed from the City of Seattle fee bracket schedule · source ↗. Impact/utility fees may apply separately.
How to apply yourself
- 1. Confirm your parcel's zoning & overlays. Run an address lookup for your City of Seattle home addition — we'll pull your specific lot polygon, zoning, setbacks, and any shoreline/ECA/historic overlays.
- 2. Assemble submittals (5).
- 3. Submit through the city portal: Seattle Department of Construction & Inspections (SDCI) ↗
- 4. Track review. Respond to reviewer comments promptly.
- 5. Pay issuance fees (Construction Permit (Addition/Alteration). Pay 75% of plan-review + permit fees at application acceptance. See SDCI 2026 Fee Estimator.) and pick up the permit. Inspection card travels with the job.
Or have Kolmo do it
We pull home addition permits in City of Seattle every month. We prepare the drawings and submittals, file with Seattle Department of Construction & Inspections (SDCI), handle reviewer comments, and build the project.
Licensed WA general contractor KOLMOL*753JS · bonded & insured
Addition permits in City of Seattle — FAQ
When does a home addition need a permit in City of Seattle?
Any additional floor area requires Construction Permit (Addition or Alteration). Plan review required. ECA + lot coverage + setback compliance verified at intake.
How much does a home addition permit cost in City of Seattle?
For a $120,000 home addition project, the estimated City of Seattle permit fee is about $4,157.15 — building fee $1,976.5 + plan review $1,976.5 + surcharges. Fees scale with project valuation per the city schedule.