Seattle-Area ADU Service and Permit Jurisdictions

A mailing address, school district or builder’s service area does not prove the permit office. First check whether the property is in Seattle, another city or unincorporated King County. That answer controls the code, forms, fees and utility planning.

This hub links to detailed local guides. It does not claim that one company covers every city or county. A city page also does not prove that an ADU is allowed on a lot.

City of Seattle

Seattle SDCI maintains the City’s ADU guidance. It explains permit paths, current code topics and the ADUniverse DADU program. Projects may also involve Seattle City Light, Seattle Public Utilities and King County sewer charges.

Use the Seattle ADU building page for the City’s lot, plan, permit and utility sequence.

King County cities and counties

King County includes Seattle, other cities and areas outside city limits. King County Local Services handles permits only for unincorporated property. Its March 2026 ADU handout separates urban-growth and rural rules, including unit numbers and possible size limits.

The King County ADU guide explains how to find the permit office before relying on County material.

Eastside cities and counties

Bellevue, Kirkland and Redmond use different ADU resources. Bellevue changed its housing and ADU rules in 2025 and is developing a ready-plan program. Kirkland already offers DADU plans. Redmond publishes its own home permit and ADU guidance.

Use the Eastside ADU guide before choosing a city page:

• Bellevue ADU building
• Kirkland ADU building
• Redmond ADU building

North and south King County cities

Shoreline

Shoreline says its zoning code allows two ADUs on a lot and requires a building permit to construct one or convert space. Its permit checklist and tree rules are different from Seattle’s. Read the Shoreline ADU guide.

Renton

Renton offers eight permit-ready ADU base plans from about 415 to 1,000 square feet and a pre-screening path. The plan still needs site-specific work and City review. Read the Renton ADU guide.

Burien

Burien’s current code allows up to two ADUs per lot and generally limits attached and detached ADUs to 1,000 square feet, subject to the live code and property. Read the Burien ADU guide.

Bothell

Bothell straddles King and Snohomish Counties but uses a City permit path for property inside City limits. The City publishes a residential ADU filing and housing details. Read the Bothell ADU guide.

Mercer Island

Mercer Island requires an ADU permit and publishes current 2026 submittal rules. Critical-area review and site conditions can affect the route. Read the Mercer Island ADU guide.

What changes between cities and counties?

The unit may look similar while the local rules change. Confirm:

• number and type of ADUs allowed.
• size, height, setbacks and lot coverage.
• tree, slope, shoreline or critical-area review.
• parking and access rules.
• title, owner-occupancy or rental provisions.
• pre-approved or permit-ready plan status.
• plan-review and trade-permit process.
• water, sewer, power and stormwater permit offices.
• local fees and external-work conditions.

Rules can change after a new state or local law. Link the project brief to the live official page and record the date checked.

How should company coverage be confirmed?

Ask for the legal business name, Washington registration number and recent work under the same permit office. “Serving Greater Seattle” does not prove local experience or that the company will take the project.

Confirm service area before sharing personal project details. Then use the builder comparison guide to review work, registration, project proof, design duty, utilities, allowances, payment terms and written warranty documents.

What should a local guide help you do?

A useful local guide should do more than repeat the city name. It should help you find the permit office, current official sources and major site limits. It should also explain plan options, utility questions, cost, timing and proof to request from a builder.

The common site check, cost and timeline guides remain part of every location choice. A city page adds local facts. It does not replace the complete list of work.

Build a dated city or county record

Local ADU pages and forms change. Save the permit office, zoning source, official ADU page, permit portal and utility companies. Add the date checked. If staff answers a key question, save the email or meeting note and the exact question.

This record matters when a company works in several cities. It separates a current local rule from a habit used elsewhere. It also gives the designer and estimator one source list.

When is a city-specific guide useful?

A city guide is useful when the local choices are truly different. The city may have its own ready-plan program, unit limits or size rules. It may also have important utility, tree, slope or shoreline issues. A city name alone does not change the building process.

If your city does not have a full guide here, start with the permit office and its current official sources. Use the King County or Eastside hub to find the right path. Do not reuse a nearby city’s checklist without checking the local rules.