Can I Build Second Story Addition in Seattle, WA? (2026)
Find out if you can build a second story addition in Seattle, WA. Rules, permit requirements, costs, and next steps.
Adding a second story in Seattle, WA is possible in most zones, subject to height limits and structural permit requirements.
A second story addition is one of the most complex home improvement projects in Seattle, WA. It requires a full building permit, structural engineering review, and must comply with the height limits for your zoning district. Unlike a ground-floor addition, a second story changes the roofline and structural load path of your entire home, triggering stricter engineering requirements. In Seattle, zone height limits range from 30 feet in SF 5000 zones — verify your zone before planning.
Second Story Addition Rules in Seattle
Second Story Addition Rules in Seattle: Building permit required: Yes — all second story additions require a permit. Permit thresholds: All structural additions to existing dwellings require permit. Example height limit (SF 5000): 30 feet, max 2 stories. Structural engineering drawings required. Setbacks apply to the full structure height. All additions increasing gross floor area require Seattle SDCI building permit. Plans must comply with zone setbacks, lot coverage, and height limits. Structural drawings required. Seattle's design review may apply for larger additions in certain design review zones.
Costs & Fees
Second story addition permit fees in Seattle: $2,000–$10,000. Note: structural engineering fees ($2,000–$10,000+) are separate from permit fees.
Timeline
Plan check: 4-10 weeks. Construction typically 3-6 months for a full second story.
Next Steps
Next steps for adding a second story in Seattle: 1. Hire a structural engineer to assess your existing foundation and framing capacity. 2. Confirm your zone height limit and verify the addition meets all setback requirements. 3. Submit full structural plans and permit application to the Seattle Department of Construction and Inspections (SDCI). 4. Inspections required at foundation reinforcement, framing, shear panels, and final.
Seattle Department of Construction and Inspections (SDCI)
Phone: (206) 684-8850
Website: https://www.seattle.gov/sdci
Online Permits: https://cosaccela.seattle.gov/portal/welcome.aspx
Frequently Asked Questions
Can I build an ADU (backyard cottage) in Seattle?
Yes. Seattle is one of the most ADU-friendly cities in the US. You can build both a Detached ADU (backyard cottage/DADU, up to 1,000 sqft) and an Attached ADU (up to 1,000 sqft) on the same lot — 2 ADUs total per Washington HB 1337. No owner-occupancy requirement. No additional parking required. Building permit from Seattle SDCI required. Pre-approved standard DADU plans are available to speed up the permit process.
What changed in Seattle's ADU rules because of Washington HB 1337?
Washington HB 1337 (effective July 2023) codified what Seattle had already done in 2019: allows 2 ADUs per single-family lot, removes owner-occupancy requirements, and eliminates parking mandates near transit. Seattle was a national leader in ADU reform before HB 1337. The state law now ensures that other Washington cities must follow Seattle's example. Seattle's existing ADU ordinance continues to govern locally.
Do I need a permit for a home business in Seattle?
No city-issued permit is required to operate a qualifying home occupation in Seattle. You may work from home as long as you have no client visits, no non-resident employees working on-site, no external evidence of the business, and your business use is incidental to the residential use. You will need a Seattle business license and a Washington State business license regardless. Cottage food operations (baked goods, jams, etc.) require Washington Dept of Agriculture registration.
Can I do short-term rentals on Airbnb in Seattle?
Yes, with a Short-Term Rental Operator's License (approximately $75/year). If you live on-site (operator-occupied), you may rent your home for an unlimited number of nights annually. Airbnb automatically collects and remits Seattle and Washington lodging taxes (combined approximately 15.6%). Display your license number on your listing. Operating without a license carries fines of $500+ per violation.
What are the setbacks in Seattle's SF 5000 zone?
In Seattle's SF 5000 zone (most common single-family zone), the front setback is 20 feet, side setbacks are 5 feet on each side, and the rear setback is typically 25 feet (20% of lot depth, minimum 20 ft, maximum 25 ft). Maximum lot coverage is 35% (plus additional allowance for DADUs). Maximum building height is 30 feet. Verify your specific parcel using SDCI's parcel data tool — shoreline, environmental overlay, or historic designation may add requirements.
Is solar required on new homes in Seattle?
No. Washington does not have a statewide new-construction solar mandate. Seattle encourages solar through streamlined permitting and incentive programs, but it is not required. Seattle City Light offers net metering and the federal Investment Tax Credit (ITC) reduces solar installation cost by 30%. Standard residential solar permits are processed quickly through SDCI.
How do I look up the zoning for my Seattle property?
Use SDCI's Parcel Information tool at seattle.gov/sdci/permits/do-i-need-a-permit/parcel-information. Enter your address to find your zoning designation, ADU eligibility, lot size, and any overlays (environmental critical areas, shoreline, landmark, flood zone). You can also view Seattle's interactive zoning map at https://www.seattle.gov/opcd/ongoing-initiatives/seattle-2035.
Source: Seattle Department of Construction and Inspections (SDCI) — Building Regulations. Last verified April 5, 2026. View source