ADU Regulations in Washington: The Complete Guide

If you’re considering adding an accessory dwelling unit (ADU) to your property in Washington, you’ll be glad to know the state ranks among the top seven most ADU-friendly in the country. Nearly every county and most cities allow ADUs in some form. In fact, the state has issued a mandate under the Growth Management Act (GMA) requiring certain jurisdictions to permit them as a way to increase affordable housing.

Still, legal approval involves more than just a green light. Each area enforces specific development standards and permitting requirements that must be met before your project can move forward. To make the process easier, we’ve compiled a comprehensive list of ADU regulations for every county in Washington, along with details for major cities. Keep reading to find out what’s allowed in your area.

Are ADUs Allowed in Washington?

Yes, House Bill 1337 requires all cities and counties fully planning under the Growth Management Act (GMA) to allow up to two ADUs on any residential lot that permits single-family homes within an urban growth area (UGA). Each ADU must be allowed up to at least 1,000 square feet, and jurisdictions cannot require the property owner to live on-site. These units may also be sold as independent units. To learn more, visit the Washington State Department of Commerce’s ADU resource page.

However, not all counties and cities must fully plan under the GMA, so these requirements do not apply statewide. If your property is outside a UGA or in a jurisdiction that does not fully plan under the GMA, ADU regulations may differ. Check with your local building or planning department to confirm what’s allowed in your area.

Below, you’ll find ADU regulations for each county in Washington, along with guidance for many cities and towns.

ADUs That Are Allowed in Washington

Most ADUs in Washington must fall between 300 and 1,500 square feet, a range that all our models comfortably meet. Browse the options below to find the model that best fits your needs.

What Is Considered An ADU in Washington?

The definition of an ADU can vary depending on where you live. Some areas permit attached, detached, or conversion ADUs, while others allow only attached units. In certain jurisdictions, park model tiny homes may qualify as ADUs, but in others, they are not permitted at all. To learn what counts as an ADU in your area, keep reading.

Can Park Model Tiny Homes Be Used As ADUs?

It depends on where you reside, some counties and cities in Washington strictly prohibit them from being used as ADUs, while others may allow them. Keep reading below to find out what your city or county allows.

If you’re considering living in a tiny home in Washington, start with our guide to local regulations. You can also explore the key differences between park model tiny homes and ADUs in our comprehensive guide.

Can Cabins From Zook Cabins Be Used As An ADU?

Yes, we have a range of models, including our ADUs, that meet the sizing requirements common in Washington state. 

Our log cabins are an excellent option. Ranging from 660 to 2,000 square feet, these are the perfect range for ADUs in Washington, which have sizing requirements ranging from a minimum of 300 square feet up to 1,600 square feet.

For a more contemporary look, our modern cabins may be a better fit. With sizes ranging from 728 to 2,110 square feet, these also fall well within the range typical to Washington state.

If you’re interested in a manufactured option, our Sonoma Luxury Mobile Home is a total of 697, which fits comfortably in the range for nearly every county in Washington.

And of course, our ADUs are specifically designed for compliance, so no matter where you live, we have a model that can meet your local requirements. Because regulations vary by city and county, be sure to check with your local officials to confirm that your selected model qualifies.

What is the Difference Between a Prefab ADU & a Modular ADU?

The difference between prefab and modular ADUs is in how they are constructed. 

• Prefab ADUs: Built completely off-site and delivered fully built
• Modular ADUs: Built off-site in sections, but fully assembled on site

If you’re curious about how prefab and modular ADUs differ, we’ve created a comprehensive guide to help answer your questions.

Size & Placement Requirements

An ADU’s defining features typically include its size and placement requirements. Because it shares a lot with another dwelling, there are often restrictions on how large it can be, how far it must be from property lines, and how close it can be to the primary structure. These requirements often vary by zoning district, so contact your local zoning officials to confirm what’s allowed. Below, we’ll outline some general guidelines.

What is the Minimum Size for an Accessory Dwelling Unit?

Most areas in Washington require ADUs to meet minimum dwelling standards set by the state or by local building codes. These typically range from 190 to 300 square feet. Because requirements vary by location, check with your local officials to confirm the minimum size allowed.

Can My ADU be Bigger Than My House?

No, in most cases an ADU cannot be larger than the primary dwelling on your property. In fact, many areas set the maximum size as a percentage of your main home’s total square footage.

Do You Need A Permit For An ADU in Washington?

Yes, in most cases, you will need a building permit, a zoning permit, or both. Some areas may also require a permit specific to ADUs. Check with your local officials to confirm which permits apply. Once you know what’s required, complete the application and ensure your ADU meets all relevant standards so your permit is approved and you’re authorized to begin construction.

Are There Any Incentives or Grants for ADUs in Washington?

While Washington does not offer statewide ADU grant programs like those in California or New York, there may be local financing options or incentives available. Check with your local officials to learn what resources might apply to your property.

Can an ADU Have Multiple Bedrooms and Bathrooms?

Yes, although Washington does place some restrictions on the number of bedrooms allowed in an ADU. If you’re considering a multi-bedroom or multi-bathroom layout, our Grove, Luna, and A-frame models all offer 1–2 bedrooms and bathrooms. Be sure to check with your local officials to confirm what’s allowed in your area.

Are ADUs A Good Investment?

Absolutely! ADUs are often a great option for rental income and, in some cases, can even be sold separately. Washington tends to have more flexible owner-occupancy rules than many other states. In some jurisdictions, both the primary residence and the ADU can be rented without the owner living on-site. Certain areas may also allow the ADU to be sold independently, although this depends on local zoning and subdivision laws. Be sure to check with your local planning department to understand what’s permitted in your area.

What Are the Requirements for ADUs in Each County in Washington?

Below are all 39 counties and whether or not they allow ADUs. It’s important to note that cities and towns within each county can enforce their own ADU regulations, so feel free to skip this list to find out what they allow.

County	Department	ADUs Allowed	Minimum Size	Maximum Size
Adams County	Building & Planning Department	Yes	1,000 sq ft	1,000 sq ft
Asotin County	Building & Planning Department	Yes	1,000 sq ft	1,000 sq ft
Benton County	Development Services	Yes	Not stated	800 sq ft or 40% of primary home
Chelan County	Community Development Department	Yes	Not stated	1,200 sq ft
Clallam County	Community Development Department	Yes	Not stated	Attached: 35% / Detached: 50% or 1,250 sq ft
Clark County	Community Development Department	Yes	Not stated	800 sq ft or 40% of primary dwelling
Columbia County	Planning & Building Department	Yes	Not stated	1,100 sq ft or 50% of primary
Cowlitz County	Building & Planning Department	Yes	Not stated	1,200 sq ft
Douglas County	Building & Construction Services	Appears permitted	Not stated	Unclear
Ferry County	Planning & Building Department	Yes	Not stated	Unclear
Franklin County	Planning and Building Department	Yes	Attached: N/A, Detached: 720 sq ft	Attached: 800 sq ft / Detached: 1,600 sq ft
Garfield County	Building & Planning Department	Yes	Unclear	Unclear
Grant County	Development Services	Yes	Unclear	Unclear
Grays Harbor County	Planning & Building Division	Yes	Not stated	Not stated
Island County	Planning & Community Development	Yes	Not stated	1,200 sq ft
Jefferson County	Community Development Department	Yes	Not stated	1,250 sq ft
King County	Permits	Yes	Not stated	1,000 sq ft
Kitsap County	Community Development Department	Yes	Inside UGA: Not stated, Outside UGA: Not stated	Inside UGA: 1,000 sq ft / Outside: 900 sq ft
Kittitas County	Community Development Services	Yes	Not stated	1,500 sq ft
Klickitat County	Code Compliance	Yes	Not stated	924 sq ft
Lewis County	Community Development Department	Yes	Not stated	1,296 sq ft
Lincoln County	Building, Planning, & Land Services	Appears permitted	Not stated	Unclear
Mason County	Community Development Department	Yes	Not stated	Attached: 1,500 sq ft / Detached: 1,200 sq ft
Okanogan County	Planning & Development Department	Yes	RS-6: Not stated	1,500 sq ft
Pacific County	Community Development Department	Yes	Unclear	RS-6: 800 sq ft / RS-11: 1,000 sq ft
Pend Oreille County	Community Development Department	Appears permitted	Not stated	Unclear
Pierce County	Planning & Public Works Department	Yes	Not stated	UGA: 1,000 / Outside: 1,250 sq ft
San Juan County	Community Development Department	Yes	As permitted by building code	1,000 sq ft
Skagit County	Planning & Development Department	Yes	Not stated	1,200 sq ft
Skamania County	Community Development Department	Yes	Not stated	1,000 sq ft
Snohomish County	Planning & Development Services	Yes	Not stated	1,200 sq ft
Spokane County	Building & Planning Services	Yes	Not stated	800 sq ft
Stevens County	Land Services	Yes	Not stated	1,000 sq ft
Thurston County	Community Planning Department	Yes	None (if within footprint)	Attached: 1,500 sq ft / Detached: 1,200 sq ft
Wahkiakum County	Building & Planning Department	Unclear	Unclear	Unclear
Walla Walla County	Community Development Department	Yes	800 sq ft (primary must meet min)	1,100 sq ft or 50% of primary
Whatcom County	Planning & Development Services	Yes	Not stated	1,248 sq ft
Whitman County	Planning Division	Yes	Not stated	1,200 sq ft or 50% of primary
Yakima County	Planning Division	Yes	Not stated	1,000 sq ft

Does Adams County Allow ADUs?

Yes, the county is fully planning, meaning it complies with the state requirements for ADUs, including allowing up to 2, at least 1,000 square feet. Contact the Building and Planning Department if you have any questions about what is permitted.

Does Asotin County Allow ADUs?

Yes, Asotin County falls under the GMA and therefore must allow:

• Up to 2 ADUs on a single-family residential lot in an Urban Growth Area
• Each ADU is to be up to 1,000 square feet
• No owner occupancy
• The ADU is to be sold as a separate unit

If you have any questions about their requirements, contact the Building & Planning Department.

Does Benton County Allow ADUs?

Yes, Benton County allows accessory dwelling units, provided that they meet the following sizing requirements:

• Maximum Square Footage: 40% of the total square footage of the single-family home or 800 square feet in size, whichever is smaller
• No more than one bedroom is permitted
• RVs or park model tiny homes are not allowed for use as an ADU
• Minimum Square Footage: Not stated

To certify compliance with all applicable ADU regulations, contact Development Services.

Does Chelan County Allow ADUs?

Yes, the county permits ADUs so long as they:

• Are no larger than 1,200 square feet
• Are not an RV or park model tiny home

To ensure your ADU will be approved, please contact the Community Development Department to learn more about all applicable requirements for your ADU.

Does Clallam County Allow ADUs?

Yes, but you must follow these guidelines when adding an ADU to your property in Callam County:

• Maximum Size:
  • Attached ADU: 35% of the gross floor area of the primary dwelling unit
  • Detached ADU: 50% of the gross floor area of the primary dwelling unit or 1,250 square feet 

Whether or not you can add an ADU to your property depends on its zoning designation. Be sure to reach out to the Community Development Department to determine if you can add an ADU to your property.

Does Clark County Allow ADUs?

Yes, but your ADU cannot exceed 800 square feet or 40% of the area of the primary dwelling’s living area, whichever is less. It can be larger depending on the zoning of your property. Contact the Community Development Department to learn more about the 

requirements specific to your zoning district.

Does Columbia County Allow ADUs?

Yes, but your ADU must comply with the following standards:

• Maximum Size: 1,100 square feet or 50% of the total square footage of the primary residence, whichever is less
• RVs/park model tiny homes are not permitted as ADUs
• Maximum Number of Bedrooms: 3
• Distance From Primary Residence: 100 feet

To certify compliance with all applicable regulations, contact the Planning & Building Department.

Does Cowlitz County Allow ADUs?

Yes, Cowlitz County is fully planning under the GMA, so ADUs within the UGA must comply with state requirements. However, the county also allows ADUs outside of these areas, though you are limited to one unit with a maximum size of 1,200 square feet.

Contact the Building & Planning Department to ensure your ADU complies with all applicable requirements.

Does Douglas County Allow ADUs?

It appears that they are allowed, but the specific guidelines are not clearly stated. Contact Building and Construction Services to find out what they allow.

Does Ferry County Allow ADUs?

Yes, Ferry County is apart of the GMA, therefore they follow the state requirements for ADUs in UGAs. However, it is unclear if they are allowed countywide. For clarity on ADU regulations in Ferry County, contact the Planning & Building Department.

Does Franklin County Allow ADUs?

Yes, Franklin County permits both accessory apartments and detached accessory dwelling units. These units must meet the following standards:

• Maximum Size: 
  • Attached: Shall not exceed 40% of the principal dwelling’s floor area or 800 square feet
  • Detached:1,600 square feet
• Minimum Size:
  • Attached: N/A
  • Detached: 720 square feet

To certify compliance with all applicable regulations, contact the Planning and Building Department.

Does Garfield County Allow ADUs?

Yes, but the requirements for adding one to your property are unclear. Contact the Building & Planning Department to find out exactly what they allow.

Does Grant County Allow ADUs?

Yes, but the sizing requirements for ADUs in unincorporated parts of the county are unclear. For clarification on what is allowed, contact Development Services.

Does Grays Harbor County Allow ADUs?

Grays Harbor County is a part of the Growth Management Act (GMA), so it permits ADUs in accordance with the Washington Department of Commerce’s requirements. To find out if ADUs are allowed outside the urban growth area (UGA), contact the county’s  Planning & Building Division.

Does Island County Allow ADUs?

Yes, but ADUs in the county are subject to the following requirements:

• No RVs or park model tiny homes are permitted as ADUs
• Maximum Size: 1,200 square feet

Additional requirements apply. Please contact the Planning & Community Development to ensure compliance with all applicable ADU regulations.

Does Jefferson County Allow ADUs?

Yes, provided that they meet the following requirements:

• Maximum Size: 1,250 square feet
• RVs/park model tiny homes are not permitted as ADUs

Additional requirements regarding owner-occupancy, permitting, and disposal services are in place. Contact the Community Development Department  to ensure compliance with all these requirements.

Does King County Allow ADUs?

Yes, but it must not exceed 1,000 square feet. Additional requirements do apply, so be sure to contact the Permits department.

Does Kitsap County Allow ADUs?

Kitsap County does permit ADUs, but has different requirements depending on if your property is inside or outside an UGA. Theses requirements are as follows:

• Inside a UGA:
  • Maximum Size: 1,000 square feet or 60% of the primary residence’s habitable area
• Outside a UGA:
  • Maximum Size: 900 square feet or not greater than 50% of the primary residence habitable area, whichever is smaller

Additional requirements are in place for location, size, design, and more, so be sure to certify compliance with the Community Development Department.

Does Kittitas County Allow ADUs?

Yes, but the ADU must be no larger than 1,500 square feet. You’ll also need to meet specific lot size, setback, and permitting requirements. Because these vary by zoning district, contact Community Development Services for details.

Does Klickitat County Allow ADUs?

Yes, ADUs in Klickitat County must meet the following requirements:

• Maximum Size: 924 square feet
• Maximum Number of Bedrooms: 2

Additional requirements may apply, so contact Code Compliance to ensure your ADU is approved.

Does Lewis County Allow ADUs?

Yes, in effort to increase housing in rural areas, Lewis County permits ADUs. However, they must comply with the following requirements:

• Maximum Size: 1,296 square feet
• Maximum Number of Bedrooms: 2

To certify compliance with all applicable regulations and gain approval for your ADU, contact the Community Development Department.

Does Lincoln County Allow ADUs?

They do appear to be permitted, but specific guidelines for adding one to your property are unclear. Contact Building, Planning, and Land Use Services for clarification on what they allow.

Does Mason County Allow ADUs?

Yes, ADUs are permitted in Mason County, provided that they meet the following requirements:

• Maximum Size:
  • Attached: 80% of the primary residence or 1,500 square feet
  • Detached: 80% of the area of the primary residence or 1,200 square feet, whichever is smaller
• No RVs or park model tiny homes may be permitted for use as ADUs

Requirements regarding setbacks, owner-occupancy, and permitting can vary by zoning district. Contact the Community Development Department to certify compliance. 

Does Okanogan County Allow ADUs?

Yes, but the ADU must be no larger than 1,500 square feet. Setback requirements and permitting vary by zoning district, so be sure to certify compliance with the Planning & Development Department.

Does Pacific County Allow ADUs?

Yes, but ADUs must adhere to specific sizing requirements based on zoning district, which are as follows:

Zoning District	Maximum Size
RS-6	800 square feet
RS-11	1,000 square feet
Attached	45% of the floor area of the primary dwelling or 800 square feet, whichever is smaller

Since requirements can vary by zoning district, it’s always recommended that you contact the Community Development Department to ensure compliance with all applicable regulations.

Does Pend Oreille County Allow ADUs?

It appears that they are permitted, but the specific requirements for placing one on your property are unclear. For clarification on what they allow, contact the Community Development Department.

Does Pierce County Allow ADUs?

Yes, Pierce County falls under the GMA and allows ADUs outside the UGA as well. However, ADU size requirements vary depending on your property’s location. 

• Maximum Size
  • In the UGA: 1,000 square feet
  • Outside the UGA: 1,250 square feet

Additional requirements apply, so be sure to contact the Planning & Public Works Department to ensure compliance with all applicable regulations.

Does San Juan County Allow ADUs?

Yes, San Juan County permits them both inside and outside of UGAs. The requirements are as follows:

• Maximum Size: 1,000 square feet

A permit is required to construct a detached ADU. Contact the Community Development Department to confirm compliance and obtain the necessary permits.

Does Skagit County Allow ADUs?

Yes, Skagit County does permit ADUs, but they must meet these development standards:

• Minimum Size: As spermitted by the building code
• Maximum Size: 1,200 square feet
• Park model tiny homes are not permitted as ADUs

Other standards are in place for ADUs within unincorporated parts of the county. Contact the Planning & Development Department to ensure that all standards are met. 

Does Skamania County Allow ADUs?

Yes, but there are certain requirements your ADU must meet:

• Maximum Size: 1,000 square feet
• Maximum Number of Bedrooms: 2

ADUs must meet all applicable building code requirements and design standards. Be sure to contact the Community Development Department to ensure your ADU meets all these standards.

Does Snohomish County Allow ADUs?

ADUs are permitted in certain urban zones within Snohomish County and must be no larger than 1,200 square feet. Other requirements regarding setbacks, number of ADUs, and more are in place, so be sure to contact the Planning & Development Services.

Does Spokane County Allow ADUs?

Yes, but there are certain requirements that you must meet:

• Maximum Size: 800 square feet
• Maximum Number of Bedrooms: 2

You must also comply with all relevant regulations in the International Residential Code and Spokane County Zone Code. To certify compliance with these requirements, contact Building & Planning Services.

Does Stevens County Allow ADUs?

Yes, you may have one ADU up to 1,000 square feet on your property in Stevens County, but it must meet all applicable zoning, setback, water, and sewage disposal requirements. In addition, park model tiny homes are not permitted as ADUs. To ensure compliance, contact Land Services.

Does Thurston County Allow ADUs?

Yes, but ADUs in Thurston County are subject to the following size limitations:

• Attached: 50% of the gross floor area of the principal residential structure
• Detached: 1,500 square feet or 40% of the principle structure, whichever is less
• Conversion: None so long as it does not exceed the footprint of the structure

Other limitations and standards are in place. Contact the Community Planning Department to ensure compliance with all applicable requirements for your ADU project.

Does Wahkiakum County Allow ADUs?

It is unclear if they are permitted in Wahkiakum County, please contact the Building & Planning Department for clarification on what is allowed.

Does Walla Walla County Allow ADUs?

Yes, ADUs are permitted in Walla Walla, but only if they meet the following requirements:

• Maximum Size: 1,100 square feet or 50% of the total square footage of the primary residence, whichever is less
• Primary residence must be at least 800 square feet to allow an ADU

To get approval for your ADU, contact the Walla Walla County Community Development Department.

Does Whatcom County Allow ADUs?

Yes, provided that it is no larger than 1,248 square feet. Additional requirements may apply, contact Planning & Development Services to ensure compliance with all applicable standards for development.

Does Whitman County Allow ADUs?

Yes, but there are certain development standards that you must meet:

• Maximum Size: 1,200 square feet or 50% of the total gross floor area of the primary residence, whichever is less
• Maximum Number of Bedrooms: 2

There are additional standards for development, so be sure to consult with the Planning Division to ensure compliance.

Does Yakima County Allow ADUs?

Yes, but the ADU can be no larger than 1,000 square feet. Setbacks and other requirements typically vary by zoning district. To certify compliance, contact the Planning Division.

Find Your Accessory Dwelling Units Requirements in Washington By Municipality

County	Department	ADUs Allowed	Minimum Size	Maximum Size
Seattle	Planning & Community Development	Yes	N/A	650–1,000 sq ft
Spokane	Building & Planning Department	Yes	250 sq ft (internal)	600–800 sq ft
Tacoma	Planning & Development Services	Yes	N/A	Up to 1,000 sq ft or 85% of primary dwelling or 15% of lot
Vancouver	Community Development Department	Yes	State minimums	800 sq ft or 50% of primary dwelling
Bellevue	Community Development Department	Yes	N/A	1,200 sq ft or 40% of combined area
Kent	City Planning	Yes	N/A	1,000 sq ft
Everett	Community, Planning, & Economic Development	Yes	N/A	1,000 sq ft
Renton	Housing Department	Yes	N/A	600–1,000 sq ft depending on lot size
Spokane Valley	Land Use and Planning Division	Yes	300 sq ft	Up to 1,000 sq ft or 10% of lot
Federal Way	Community Development Department	Yes	N/A	1,000 sq ft
Yakima	Planning Division	Yes	N/A	Up to 1,000 sq ft or size of primary structure
Kirkland	Planning & Building Department	Yes	N/A	1,200 sq ft
Bellingham	Planning & Community Development	Yes	N/A	1,000 sq ft
Auburn	Zoning & Land Use Department	Yes	300 sq ft	1,000 sq ft
Kennewick	Community Planning Department	Yes	N/A	1,100 sq ft

Does Seattle allow ADUs?

Yes, the city does permit ADUs. However, they are subject to the following requirements:

• Maximum Size: 1,000 square feet in a neighborhood residential zone or 650 square feet in a lowrise zone

Additionally, all ADUs must meet the Seattle residential, building, mechanical, electrical, energy, land use, and other applicable requirements. Contact the Planning & Community Development to certify compliance. 

Does Spokane allow ADUs?

Yes, but they outline certain development standards, including:

• Minimum Lot Size: 5,000 square feet
• Minimum Size:
  • Internal: 250 square feet
  • Detached: N/A
• Maximum Size:
  • Internal: 800 square feet
  • Detached: 600 square feet

Setbacks are often determined by zoning district. Additionally, a permit likely needs to be obtained. Contact the Building & Planning Department to certify compliance and obtain the required permits.

Does Tacoma allow ADUs?

Yes, the city does permit ADUs, provided that:

• Maximum Size Does Not Exceed:
  • 15% of the lot area
  • 85% of the living area of the primary dwelling
  • 1,000 square feet

There are additional requirements for setbacks, design, and more, so be sure to contact Planning & Development Services to ensure you meet all applicable development standards.

Does Vancouver allow ADUs?

Yes, but they are only legal with an established building permit. In addition, there are certain requirements your ADU must meet to receive approval on your permit application. These are as follows:

• Minimum Size: No less than the requirements set forth in the Washinton State Building Code
• Maximum Size: 800 square feet or 50% of the primary single-family residence, whichever is less

Additional requirements regarding setbacks, placement, and design are in place, so be sure to consult with the Community Development Department to ensure your building permit application is approved.

Does Bellevue allow ADUs?

Yes, ADUs are allowed with a building permit, so long as they meet the following requirements:

• Maximum Size: 1,200 square feet or 40% of the combined area of the ADU and primary residence, whichever is larger
• Detached ADUs are not permitted

The type of permit required depends on the scope of the work, so be sure to consult with the Community Development Department.

Does Kent allow ADUs?

Yes, so long as they are no larger 1,000 square feet. Additional standards are in place, so be sure to confirm compliance with City Planning.

Does Everett allow ADUs?

Yes, as long as the ADU is no larger than 1,000 square feet. Additional requirements may apply depending on your zoning district, and a permit is likely required. Contact the Community, Planning & Economic Development Department to verify that all applicable regulations are met.

Does Renton allow ADUs?

The city of Renton does allow ADUs, but the maximum size depends on the lot area of your property. The requirements based on lot size are as follows:

Lot Area	Maximum ADU Size
3,000 square feet or less	600 square feet
3,001-4,999 square feet	700 square feet
5,000-6,999 square feet	900 square feet
7,000-8,999 square feet	800 square feet
Greater than 9,000 square feet	1,000 square feet

Additional requirements vary depending on your zoning district. Contact the Housing Department to get approval for your ADU plans before you begin building.

Does Spokane Valley allow ADUs?

Yes, so long as your ADU follows these sizing guidelines:

• Maximum Size: 50% of the habitable square footage
• Minimum Size: 300 square feet
• ADU Footprint: 10% of the lot area or 1,000 square feet, whichever is greater
• Maximum Number of Bedrooms: 2

Additional setback and design requirements apply to ADUs, so consult the Land Use & Planning Department to ensure compliance with all applicable regulations.

Does Federal Way allow ADUs?

Yes, but Federal Way has certain requirements regarding size, including:

• Maximum Size:
  • Detached: 1,000 square feet
  • Attached: 1,000 square feet or the maximum of the largest floor area of the primary dwelling unit
• Maximum Number of Bedrooms: 2

Additional requirements are likely in place regarding permitting, setbacks, and design. Contact the Community Development Department to learn more about the requirements for your ADU project.

Does Yakima allow ADUs?

Yes, Yakima does allow ADUs, provided that they are no larger than 1,000 square feet or does not exceed the size of the primary structure.

Does Kirkland allow ADUs?

Yes, both attached and detached ADUs are permitted, as long as they are no larger than 1,200 square feet. Additional development standards apply and vary by zoning district. Contact the Planning & Building Department to find out what requirements apply to your property.

Does Bellingham allow ADUs?

Yes, so long as the ADU is no larger than 1,000 square feet. To learn more about ADU requirements in Bellingham, contact the Planning & Community Development Department.

Does Auburn allow ADUs?

Yes, provided that they adhere to the following size requirements:

• Maximum Size: 1,000 square feet
• Minimum Size: 300 square feet

Additional standards apply to design, placement, and setbacks. To confirm compliance with all applicable regulations, contact the Zoning & Land Use Department.

Does Kennewick allow ADUs?

ADUs are permitted in Kennewick so long as they are not more than 1,100 square feet. To learn more about applicable requirements, contact the Community Panning Department.

Searching For An ADU Builder Serving Washington?

If you’re looking for an ADU builder that makes the process seamless—from ensuring code compliance to final placement on your property—you’re in the right place. At Zook Cabins, our ADU models range from 571 to 848 square feet, well within Washington’s permitted size limits. As a modular builder, we construct each unit off-site in sections, then assemble it on your property for a faster, more efficient setup.

Every ADU comes fully furnished and includes customizable features, making flexible, independent living more accessible than ever. Browse our ADU models or contact our sales team to get started today.

If our ADUs aren’t quite your style, many of our luxury mobile homes and select modern or log cabins also meet Washington state requirements.

Getting the home of your dreams has never been easier.

Tiny Home & ADU Rules By State: See How They Compare?

In Washington, rules for ADUs and park model tiny homes differ greatly. While some areas allow park model tiny homes, ADUs, and park model tiny homes as ADUs, there are some areas in Washington that prohibit park model tiny homes altogether. To see how tiny home laws in Washington compare to the state’s rules for ADUs, check out our comprehensive guide linked in the chart below.

If you’re not sure which state is right for you, see how the regulations for tiny homes vary across the U.S.