Addition permits in Seattle: fees, timeline & requirements (2026)

When does a home addition need a permit in Seattle?

Any additional floor area requires Construction Permit (Addition or Alteration). Plan review required. ECA + lot coverage + setback compliance verified at intake.

How long a home addition permit actually takes in Seattle

349 permits with plan review issued in the last 12 months: half were issued within 83 days of application and 80% within 154. At the median, 49 days were with the City and 29 with the applicant answering corrections. Typical review cycles: 3; 2% were issued on the first review. 110 permits over the counter (subject-to-field-inspection) issued in the last 12 months: half were issued within 2 days of application and 80% within 13. At the median, 2 days were with the City and 0 with the applicant answering corrections.

Days from application to issue, measured by Kolmo from City of Seattle issued building permits, data.seattle.gov dataset 76t5-zqzr.

How Seattle adopted this rule

The threshold comes from the state code (WAC 51.51), which 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

1. Footing
2. Foundation
3. Framing
4. Rough-in (electrical/plumbing/mechanical)
5. Insulation
6. Drywall
7. Final

Contractor specialties needed

General contractor · Electrician (journey-level 01 or residential 02) · Plumber · Mechanical contractor

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 Seattle

Worked example for a $120,000 home addition project (building permit). Your actual fee scales with project valuation.

Where an addition needs an SDCI permit, it is a construction permit with full plan review. SDCI prices the building permit on the value of the work through its Development Fee Index: $1,821.50 for the first $100,000, plus $7.75 for each $1,000 more to $250,000 and $7.50 per $1,000 to $500,000 ($2,984 at $250,000). With full plan review, the permit fee and the plan review fee are each 100% of the index, minimum $292; half the permit fee and all of the plan review fee are due at application. A 5% technology fee is added to every SDCI fee, and the state building code fee is $6.50 on a residential permit (SMC 22.900; RCW 19.27.085). A $150,000 addition comes to about $4,645 before trade permits. SDCI, not L&I, issues the electrical permit: $26.28 for each new or altered branch circuit up to 25 amps and $43.80 for 30 to 50 amps, plus a $55.48 administrative fee, minimum $105.12. Plumbing and gas piping permits come from Public Health – Seattle & King County, which sets and collects their fees. Computed from Seattle's adopted fee schedule · source ↗. Land use, fire and engineering review, intake, impact and utility fees, where they apply, are charged separately.