Seattle, WA - ADU Regulations

Rules and regulations for building an ADU.

ADU info for

Seattle

  • ADU allowed?
    YES
  • Number of ADUs allowed?
    1 ADU and 1 JADU
  • Max ADU Size
    1,200 SQFT
  • Eligibility
    most single-family and multi-family zoned properties
  • Setbacks
    minimum 4-foot setback from the side and rear property lines
  • Parking Requirements
    limited requirements, especially if the property is near public transit
  • ADU allowed?
    YES
  • Number of ADUs allowed?
    1 ADU
  • Max ADU Size
    750 SQFT
  • Eligibility
    R-5, R-4, and R-4A-zoned lots
  • Setbacks
    minimum 7-foot setback from the side and 15-foot rear property lines
  • Parking Requirements
    limited requirements, especially if the property is near public transit
  • ADU allowed?
    YES
  • Number of ADUs allowed?
    2 ADU
  • Max ADU Size
    1,000 SQFT (typically)
  • Eligibility
    Most residential zones
  • Owner Occupancy
    not required*
  • ADU allowed?
    YES
  • Number of ADUs allowed?
    1 ADU
  • Max ADU Size
    800-900 SQFT (typically)
  • Eligibility
    Varies but typically cities with population over 2,500; Counties over 15,000
  • Owner Occupancy
    Not required for most cases
  • Key Note
    Urban Growth Boundaries (UGBs) affect development location
  • ADU allowed?
    YES
  • Number of ADUs allowed?
    1 ADU
  • Max ADU Size
    Read details below.
  • Eligibility
    Read details below.
  • Setbacks
    Read details below.
  • Parking Requirements
    limited requirements, especially if the property is near public transit

Understand ADU zoning rules for

Seattle

With Gather, designing your ideal ADU is a breeze. We manage all the planning and permitting paperwork, ensuring you enjoy a seamless experience and complete peace of mind.

Talk to a zoning expert
Schedule a free 30-minute call or call us now (323) 591-3717

Different types of ADUs allowed in

Seattle

Though backyard homes are typically the most familiar, ADU structures come in various types. The illustration below shows the four primary types of ADU structures.

ADUs can be built using a variety of construction methods, including pre-fabricated, modular, shed, container, panelized (in pieces), and stick-built. Each construction method has its own advantages and disadvantages in terms of cost, time, and customization.

detached adu
Detached ADU
garage conversion adu
Garage Conversion ADU
addition / attached adu
Addition / Attached ADU
detached adu
Detached ADU
garage conversion adu
Garage Conversion ADU
addition / attached adu
Addition / Attached ADU
detached adu
Detached ADU
garage conversion adu
Garage Conversion ADU
addition / attached adu
Addition / Attached ADU
detached adu
Detached ADU
garage conversion adu
Garage Conversion ADU
addition / attached adu
Addition / Attached ADU

ADU regulations for

Seattle

In a proactive effort to combat the ongoing housing crisis, the State of California has adopted specific regulations to promote the construction and utilization of Accessory Dwelling Units (ADUs). Here's an expanded and comprehensive breakdown of the key points:

1. Purpose and Prominence: California recognizes the potential of ADUs in providing affordable housing options. Given the state's dense urban centers and escalating property prices, ADUs present a viable solution to address the growing demand for residential spaces.

2. Eligibility for Establishment: Both single-family homes and multifamily properties can host an ADU.

3. Size Considerations: For detached ADUs, the maximum allowable size is up to 1,200 square feet.
The actual size of an ADU might vary depending on specific factors such as the total lot area and the size of the primary dwelling on the property.

4. Parking Norms: The state mandates limited parking requirements for ADUs.
If an ADU is situated near public transit, these parking stipulations may be even less stringent, facilitating easy construction and usage.

5. Owner-Occupancy: Historically, some jurisdictions required the property owner to live in either the primary home or the ADU. However, for ADUs permitted between 2020 and 2025, the state does not enforce such owner-occupancy requirements, allowing for greater flexibility in usage.

6. Setback Rules: For detached ADUs, there's a minimum setback requirement of 4 feet from both the rear and side yard boundaries.

7. Approval Process: Cities across the state are obligated to approve compliant ADU applications within a span of 60 days. This streamlined process ensures quick turnarounds and encourages homeowners to consider ADU development.

8. Fee Structure: To further incentivize ADU establishment, the state has reduced or completely waived fees for ADUs that are less than 750 square feet. This can translate to significant savings for property owners.

9. Rental Conditions: If an ADU meets the stipulated requirements laid out by the city, it must be available for rental. This regulation ensures that ADUs actively contribute to alleviating housing shortages.

10. Local Jurisdictional Variances: While the above guidelines provide a general framework, it's crucial to note that local jurisdictions might have their unique sets of regulations and requirements. Property owners should consult their respective city or county planning departments to get precise and localized information.

In conclusion, as California grapples with housing challenges, ADUs offer a promising avenue to augment living spaces without the need for expansive new developments. These guidelines, though comprehensive, serve as a starting point, and it's always recommended to liaise with local experts for tailored advice.

State laws (RCW 36.70A.680 and 36.70A.681) mandate that all local governments under the Growth Management Act (GMA), irrespective of size and including both cities and counties within unincorporated urban growth areas, update their regulations to align with specific criteria within six months following their scheduled update. The key directives include:

  1. ADUs per Lot: Urban areas within the GMA must allow at least two ADUs on any lot that qualifies by size, in addition to the main residence. These ADUs can be attached, detached, or a mix, and converting structures like garages into ADUs must be permitted.
  2. Size Requirements: ADUs cannot be restricted to under 1,000 square feet.
  3. Design and Location Standards: Restrictions on setbacks, lot coverage, tree preservation, or entrance placements cannot be stricter than those for the main home.
  4. Street Upgrades: ADUs cannot be subjected to demands for street improvements as a permit condition.
  5. Owner Occupancy: Requirements for the homeowner to live on-site are prohibited for both the main and accessory units.
  6. Condominium Sales: It’s not allowed to block the sale of a condominium developed as an ADU on the basis that it’s an ADU.
  7. Design Review: ADUs cannot face stricter aesthetic or design criteria than the primary residence.
  8. Parking: Parking requirements are limited, with specific conditions for smaller lots and exemptions for ADUs near major transit hubs.
  9. Impact Fees: Charges for ADUs are capped at 50% of those for the main house.
  10. Common Interest Communities: New developments with homeowners associations are barred from implementing rules against ADU construction. However, existing regulations can remain.

These regulations aim to encourage the development of ADUs, offering more housing options within urban growth areas.

Since July 1, 2018, most Oregon cities and counties allow homeowners to build Accessory Dwelling Units (ADUs) on residential properties. However, local rules on ADU size, placement, and design must be followed. Each area has its own rules for:

  1. How big the ADU can be;
  2. Where it can be located; and
  3. If it needs to look like the main house.

Local governments also have different processes for giving permits and may charge fees for building an ADU. These fees, including impact fees or system development charges, can vary a lot. Some places might not charge these fees at all, while others could charge $15,000 or more for each ADU.

In Oregon, the rules for creating Accessory Dwelling Units (ADUs) set standards to boost housing while keeping communities looking good. Understanding Oregon's ADU laws is crucial for compliance and making the most of ADU benefits. Cities must have over 2,500 people, and counties over 15,000, to fall under the ADU mandate. This supports urban housing needs. Urban Growth Boundaries (UGBs) define where ADUs can be built, promoting smart growth and land use without harming Oregon's landscapes.

Oregon's ADU laws aim to increase affordable housing. They require local governments to process ADU applications efficiently, especially in urban areas. State laws stop local rules from demanding owners live in ADUs or provide extra parking, except for vacation rentals. Setback requirements ensure ADUs are well-placed, respecting privacy and the environment. Oregon encourages updating local ADU rules to match state standards, making it easier to build ADUs and help with housing shortages.

Design and siting rules for Oregon ADUs ensure they fit well with urban settings and offer design flexibility. Oregon prefers less restrictive rules for ADUs compared to other buildings, aiming to increase housing options responsibly. The state simplifies ADU regulations, replacing complex zoning laws with clearer, state-wide standards. This helps reduce red tape and encourage ADU construction.

Oregon's approach to ADUs, including size restrictions and utility connection guidelines, is designed to integrate ADUs smoothly into neighborhoods, addressing housing needs. ADUs can't be too large compared to the main house, and shared utility connections are encouraged to keep costs down. This effort shows Oregon's commitment to innovative, affordable housing solutions.

  • Oregon ADU laws establish criteria to support housing while maintaining community aesthetics.
  • Cities over 2,500 people, and counties over 15,000, need to allow ADU construction per state mandates.
  • Urban Growth Boundaries (UGBs) are key to ADU development, limiting expansion within set geographic areas.
  • The state prohibits local ordinances from requiring owner occupancy or off-street parking for ADUs, except for vacation rentals.
  • Oregon mandates setback requirements for ADUs to ensure privacy and environmental standards.
  • Local governments in Oregon must update regulations to align with state ADU codes, promoting consistent and simplified ADU development.
  • Oregon ADU laws facilitate affordable housing by removing barriers to ADU construction and simplifying the application process.
  • Design standards for ADUs in Oregon are clear and objective, not requiring ADUs to mimic the primary residence's architecture.
  • Oregon's policies allow ADUs more flexibility in development compared to other accessory structures, avoiding strict lot size or coverage constraints.
  • ADUs in Oregon are subject to size limitations, generally not exceeding 75-85% of the primary dwelling's floor area, with specific square footage caps.
  • The state encourages the use of shared utility connections for ADUs to lower construction and development costs.
  • Oregon's comprehensive ADU regulations aim to expand housing options, reduce bureaucracy, and accommodate the state's diverse housing needs.
  • Why Homeowners Choose Gather

    Your one-stop ADU platform

    With Gather, you're not just building an ADU — you're cultivating peace of mind. Our end-to-end guidance and ongoing support mean every decision is informed, every step is intentional, and every outcome exceeds expectations. With us, your dream ADU is within reach. Here is what we do:

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    Design your perfect ADU

    With Gather, designing your ideal ADU is a breeze. We manage all the planning and permitting paperwork, ensuring you enjoy a seamless experience and complete peace of mind.

    Schedule a free ADU consultation
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    City Snapshot

    Seattle

    779,200
    Population
    Median Household Income

    Seattle, known as the "Emerald City," is the largest city in the Pacific Northwest. Nestled between Puget Sound and Lake Washington, Seattle is renowned for its stunning natural beauty, thriving tech scene, and vibrant cultural landscape. The city's unique blend of urban sophistication and outdoor adventure makes it a distinctive destination in the United States.

    Population: Seattle has a population of approximately 779,200 residents. The greater Seattle metropolitan area, including nearby cities like Bellevue and Tacoma, is home to about 4 million people, making it a significant urban center in the region.

    Local Economy: Seattle's economy is diverse and robust, driven by several key sectors:

    1. Technology: Home to tech giants like Amazon and Microsoft (in nearby Redmond), Seattle is a major tech hub.
    2. Aerospace: Boeing, though headquartered in Chicago, still has a significant presence in the area.
    3. Retail: Nordstrom and Costco are headquartered in the region.
    4. Coffee: Starbucks and numerous independent roasters contribute to Seattle's coffee culture.
    5. Biotechnology and Healthcare: The city has a growing biotech sector and several major healthcare institutions.
    6. Maritime Industry: Seattle's port is one of the largest in North America.

    Popular Neighborhoods:

    1. Capitol Hill: Known for its vibrant nightlife, LGBTQ+ community, and eclectic atmosphere.
    2. Ballard: A former Scandinavian fishing village, now popular for its trendy restaurants and microbreweries.
    3. Fremont: An artsy area known for its quirky public art, including the famous Fremont Troll.
    4. Queen Anne: An affluent area offering stunning views of the city skyline.
    5. West Seattle: A more relaxed area with beautiful beaches and a small-town feel.
    6. Belltown: A dense urban neighborhood known for its high-rise condos and bustling nightlife.

    Real Estate Overview: Seattle's real estate market is one of the most competitive in the nation. The median home price is around $825,000, reflecting the city's desirability and strong job market. The rental market is equally robust, with high average rents compared to national standards. The city has seen significant development in recent years, particularly in high-rise apartments and condos in the urban core.

    Landmarks and Attractions:

    1. Space Needle: The iconic 605-foot-tall observation tower, symbol of the 1962 World's Fair.
    2. Pike Place Market: One of the oldest continuously operated public farmers' markets in the U.S.
    3. Chihuly Garden and Glass: A museum showcasing the studio glass of Dale Chihuly.
    4. Museum of Pop Culture (MoPOP): A museum dedicated to contemporary popular culture.
    5. Seattle Center: An arts and entertainment center that hosts numerous festivals and events.
    6. Olympic Sculpture Park: A nine-acre outdoor sculpture museum and beach.

    ADU Regulations in Seattle:

    Seattle has been a pioneer in promoting ADUs, with some of the most permissive regulations in the country:

    1. Zoning: ADUs are permitted in all single-family zones.
    2. Number of ADUs: As of 2019, up to two ADUs are allowed on a single-family lot - either two attached ADUs or one attached and one detached.
    3. Size Limits: Detached ADUs can be up to 1,000 square feet in size, or 800 square feet if there's a second ADU on the property. Attached ADUs can be up to 1,000 square feet, not to exceed 75% of the main house's footprint.
    4. Parking: No additional parking is required for ADUs.
    5. Owner Occupancy: As of 2019, there is no owner-occupancy requirement.
    6. Streamlined Process: The city offers pre-approved plans to expedite the permitting process.
    7. Incentives: Impact fees are waived for ADUs, and the city provides resources to help homeowners navigate the development process.

    These progressive regulations have led to a significant increase in ADU construction in Seattle, helping to address the city's housing shortage.

    Unique Aspects of Seattle:

    Seattle's identity is strongly tied to its natural surroundings. The city is flanked by water on two sides and surrounded by mountains, offering easy access to outdoor activities like hiking, kayaking, and skiing. This proximity to nature influences the city's culture, with a strong emphasis on environmental conservation and outdoor recreation.

    The city's infamous rainy weather, while often exaggerated, has shaped its culture. Seattle's coffee culture, grunge music scene, and numerous indoor attractions have all been influenced by its climate.

    Seattle is known for its progressive politics and activism. The city has been at the forefront of movements for social justice, environmental protection, and labor rights. It was one of the first major cities to implement a $15 minimum wage.

    The influence of Native American cultures is more prominent in Seattle than in many other U.S. cities. This is reflected in public art, place names, and cultural institutions like the Burke Museum.

    Seattle's food scene is diverse and innovative, with a strong emphasis on fresh, local ingredients. The city is famous for its seafood, particularly salmon and oysters, as well as its craft beer and wine industries.

    Despite its rapid growth and tech-driven economy, Seattle maintains a strong sense of neighborhood identity. Each area of the city has its own distinct character, from the bohemian vibe of Fremont to the historic charm of Pioneer Square.

    In conclusion, Seattle offers a unique blend of natural beauty, technological innovation, and progressive urban living. Its forward-thinking ADU regulations reflect the city's commitment to addressing housing challenges creatively. While it faces challenges related to growth and affordability, Seattle continues to be a dynamic and influential city, shaping trends in technology, culture, and urban development in the Pacific Northwest and beyond.

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    Frequently Asked Questions

    What is an ADU and how can you help me build one?

    An ADU, or Accessory Dwelling Unit, is also known as a tiny home, granny flat, in-law unit, or garage apartment. We help homeowners by providing expert guidance and tools to navigate the process of building an ADU, from zoning and permitting, to design and size considerations, to cost estimation, and through the construction process itself.

    How can I determine if my local area allows for ADU construction?

    Our services include assistance with zoning and permitting. We help you identify your property's specific zoning requirements and the necessary permits for ADU construction, ensuring your project stays compliant with local regulations.

    What does the construction process for building an ADU look like?

    We offer information and resources on the construction process, timelines, and best practices for building an ADU. Additionally, we have a network of trusted builders you can partner with to ensure a seamless, efficient, and high-quality build for your ADU.

    What is included in your feasibility report for building an ADU?

    With the Gather Feasibility Report, you can confidently embark on your ADU journey, knowing you've got a solid foundation and a clear roadmap to success. Let us help you transform your space into a functional, comfortable, and profitable asset today.

    We
       
    1) Thoroughly analyze your property records for a tailored assessment,        
    2) Work with city and county authorities on your behalf for a hassle-free experience,        
    3) Secure a preliminary "pre-approval" from city/county for your peace of mind,        
    4) Deliver a comprehensive report document detailing your property's ADU possibilities.            

    Embark on your ADU adventure with Gather ADU, and make the most of your property's potential without the stress or hassle.

    Do I have to commit to the entire ADU construction project right away?

    No, it isn't required. GatherADU offers support at every step of the ADU process, allowing you to proceed without making an immediate full commitment. You have the flexibility to progress at your own pace and opt for pay-as-you-go.

    Where does GatherADU operate?

    GatherADU provides ADU design and planning services nationwide with focus on California, Washington, Oregon, and Georgia.