Fees
Estimated city fees
Baseline for a simple permitted addition: $800–$3,000+ estimated city fees for a permitted residential addition in Seattle. Fees vary by project valuation and scope, and trade permits are billed separately.
| Fee | Amount | Notes |
|---|---|---|
| Building permit (valuation-based) | $800–$3,000+ (estimated range for typical room addition) | Seattle permit fees are based on declared project valuation using a published fee schedule. A modest single-room addition typically falls in this range. Larger or more complex additions with structural work cost more. Check current amounts with SDCI's fee estimator at seattle.gov/sdci. |
| Plan review fee | 65% of permit fee (estimated, charged at submittal) | Seattle charges a plan review deposit at submittal. The balance is due when the permit is issued. Complex additions may need multiple review cycles. |
| Mechanical permit | $150–$500 (estimated) | Required for HVAC extensions, new ducts, or equipment. Fees vary by scope. |
| Electrical permit | $150–$600 (estimated) | Required for new circuits, panels, or service changes associated with the addition. Filed separately with SDCI's electrical division. |
| Plumbing permit | $150–$500 (estimated) | Required for any new bathroom, laundry connections, or wet areas in the addition. |
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Conditions
The rules that apply
- A building permit is required for any addition that increases the living area or gross floor area of a residential structure.
- The Seattle Department of Construction and Inspections (SDCI) requires a building permit for any structural alteration, including new exterior walls, roof expansion, or foundation extension for an addition.
- Additions that add a bathroom, kitchen, or wet bar require plumbing permits in addition to the building permit.
- Additions that extend or add HVAC, ductwork, or mechanical equipment require a mechanical permit.
- New electrical circuits, panels, or service upgrades associated with the addition require a separate electrical permit.
- Additions must meet Seattle's Residential Code zoning requirements for the specific zone, including setbacks, lot coverage, height limits, and floor area ratio (FAR).
- Properties in designated historic districts, landmarks, or special review zones may need review from the Seattle Landmarks Preservation Board before you can get permits.
- Additions in designated flood hazard areas (FEMA Special Flood Hazard Areas) require floodplain development review.
- Energy code compliance under the Washington State Energy Code (WSEC) is required for all conditioned additions.
Documents
What you'll need to file
- Building permit application submitted through SDCI's Seattle Services Portal.
- Site plan showing lot dimensions, property lines, setbacks, existing structures, impervious surface, and the proposed addition footprint.
- Floor plans for all affected levels showing existing and proposed layout, room dimensions, and window and door locations.
- Exterior elevations showing existing and proposed building height, wall materials, and roof profile.
- Foundation and framing plan with structural details appropriate to the scope of work.
- Energy code compliance worksheet or documentation under the Washington State Energy Code.
- Structural calculations or engineer-stamped drawings if the addition involves non-prescriptive spans, moment frames, or hillside conditions.
- Geotechnical report if the site is in a liquefaction-prone area or has steep slopes.
- Plumbing, mechanical, and electrical plans if trade work is included in the scope.
- Certificate of Insurance from contractor or owner-builder declaration if the homeowner is acting as general contractor.
Process
How the permit process works
Each step must finish before the next one starts.
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Check zoning to see what is allowed Use SDCI's Parcel Data portal to look up your zoning designation, setbacks, height limits, lot coverage, and floor area ratio. Before you spend money on drawings, check how large an addition Seattle zoning allows relative to the lot and existing structure.
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Hire a designer or architect Most Seattle room additions need architectural drawings prepared and stamped by a Washington-licensed architect or residential designer. Larger or more complex additions typically also need a structural engineer.
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Prepare a complete permit package Before submitting, assemble the site plan, floor plans, elevations, structural details, energy compliance documentation, and all trade permit applications (electrical, mechanical, plumbing). Incomplete packages slow review.
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Submit through the Seattle Services Portal Create or log into your account at seattle.gov/sdci, start a new building permit application for a residential addition, upload all documents, and pay the plan review deposit. SDCI then routes the submittal to the assigned reviewers.
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Respond to plan review corrections SDCI reviewers check zoning compliance, structural adequacy, energy code, and life safety. Correction notices come through the portal. Respond promptly with updated drawings and resubmit each cycle.
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Pay remaining permit fees and receive the permit Once all reviewers approve, SDCI calculates the final permit fee. Pay the balance and download the issued permit. Post the permit visibly on site before any construction begins.
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Schedule inspections at required milestones Request inspections through the Seattle Services Portal at each required stage: typically foundation/footings, framing, insulation, and final. Trade inspections (electrical, plumbing, mechanical) have their own milestone requirements. Do not cover work before inspection.
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Pass final inspection and close the permit After all final inspections pass, SDCI closes the permit. Keep the final inspection approval for your records. You will need it for insurance claims, refinancing, and resale.
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Tools & materials
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Provenance
Code basis & official sources
Last verified 2026-05-07.
2021 Seattle Residential Code (SRC) and Seattle Building Code (SBC) as adopted with local amendments. Washington State Energy Code (WSEC) 2021 edition. Seattle Land Use Code (SMC Title 23) for zoning compliance.
Residential permit page: https://cosaccela.seattle.gov/portal/welcome.aspx
If you skip the permit
- SDCI can issue a stop-work order and require removal of completed work built without a permit.
- Unpermitted additions may need to be fully opened up (walls, insulation, framing) for retroactive inspection, which makes after-the-fact permitting expensive.
- Seattle home inspectors and title reviewers routinely flag unpermitted additions, which can block financing or sale.
- Insurance carriers may deny claims involving unpermitted living space.
- An unpermitted addition may not be counted toward the home's livable square footage in an appraisal, reducing the property's appraised value.
- Structural failures in unpermitted work can expose the homeowner to personal liability if occupants or visitors are injured.
FAQ
Common Seattle addition permit questions
Do I need a permit to add a room to my house in Seattle?
Yes, always. Any addition that increases the living area or structural footprint of a Seattle residential building requires a building permit from SDCI. There is no size exemption for room additions.
How much does an addition permit cost in Seattle?
Seattle permit fees are valuation-based. For a modest room addition, estimate $800–$3,000+ in city permit and plan review fees. Complex or large additions cost more. Trade permits (electrical, plumbing, mechanical) are billed separately. Use SDCI's online fee estimator for a current estimate.
How long does Seattle plan review take for a room addition?
Standard residential addition review at SDCI typically takes 4–8 weeks per review cycle. Total project timing, including correction cycles, permit issuance, construction, and inspections, commonly runs 3–6 months. Projects in special review zones take longer.
Do I need an architect for a home addition in Seattle?
For most room additions, yes. Seattle requires plans prepared by a Washington-licensed architect or residential designer. For additions with non-prescriptive structural elements, you may also need an engineer. Owner-drawn plans are generally not accepted for permitted additions.
What zoning rules limit how large my addition can be?
Seattle zoning sets lot coverage, floor area ratio (FAR), setbacks, and height limits, which together cap how large an addition can be. Before designing, look up your parcel on SDCI's Parcel Data viewer to see the limits for your zone.
Do I need a separate electrical permit for the addition?
Yes. Any new circuits, subpanels, or service upgrades for the addition require a separate electrical permit from SDCI. Plumbing and mechanical work also require their own trade permits, filed alongside or after the main building permit.
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Disclaimer: Informational only, not legal advice. Rules change. verify with Seattle permitting staff before you build.