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Get ADU QuoteOr call: (323) 591-3717On March 19, 2025, the Snohomish County Council unanimously passed Ordinance 25-014, a landmark decision to revise accessory dwelling unit (ADU) regulations, opening the door for more property owners to build these versatile housing units. Sponsored by Council Vice Chair Megan Dunn, the ordinance aligns with Washington State’s ongoing efforts to address the housing affordability crisis by expanding opportunities for ADU construction in urban zones. This move not only supports the state’s Growth Management Act (GMA) but also promotes diverse housing options for families, seniors, and individuals across economic segments. Below, we explore the details of this ordinance, its implications for Snohomish County residents, and how it fits into broader housing trends.
Accessory dwelling units, commonly known as ADUs, are secondary housing units located on the same lot as a primary residence, such as a single-family home, duplex, or attached single-family dwelling. These units can be attached (sharing a wall with the principal unit) or detached (a separate structure) and must include facilities for living, sleeping, cooking, and sanitation. ADUs are often referred to as "granny flats," "in-law suites," or "backyard cottages" and serve as a flexible housing solution for multigenerational families, renters, or homeowners seeking additional income.
In Snohomish County, ADUs have been permitted since 1992, initially as attached units, with detached ADUs allowed in 1994. However, prior regulations limited ADUs to lots with single-family dwellings. Ordinance 25-014 expands these permissions, allowing ADUs on lots with duplexes and single-family attached dwellings in urban zones, removing restrictive architectural standards, and aligning county codes with state mandates.
Ordinance 25-014 introduces several significant updates to the Snohomish County Code (SCC) to facilitate ADU construction. Here’s a breakdown of the key amendments:
The ordinance revises SCC Section 30.28.010 to allow ADUs on lots with single-family dwellings, single-family attached dwellings, and duplexes in urban zones. The configurations permitted include:
This expansion significantly increases housing density options in urban areas, supporting infill development and reducing pressure on rural lands.
Previous regulations required ADUs to match the architectural style of the primary dwelling, including exterior materials, roof form, and window proportions. Ordinance 25-014 removes these aesthetic requirements (SCC 30.28.010(1)(f) and (g)) to comply with RCW 36.70A.681(1)(h), which prohibits imposing stricter aesthetic standards on ADUs than on principal units. This change reduces barriers to ADU construction, making it easier and more cost-effective for property owners.
To incentivize ADU development, the ordinance increases the maximum lot coverage to 55% and reduces setback requirements:
These changes make it easier to fit ADUs on smaller lots, particularly in urban areas with limited space.
The ordinance aligns SCC definitions with state law (RCW 36.70A.696) by updating terms like "Accessory Dwelling Unit," "Attached Accessory Dwelling Unit," and "Detached Accessory Dwelling Unit." It also introduces a new definition for "Principal Unit" in SCC 30.91P.307, clarifying the relationship between primary residences and ADUs. Additionally, SCC 30.28.070 now allows nonconforming structures to be converted into ADUs, further expanding opportunities for utilizing existing buildings.
By removing the owner-occupancy requirement (RCW 36.70A.681(1)(b)) and allowing more flexible ADU configurations, the ordinance supports affordable housing. ADUs often provide below-market-rate rentals, serving seniors, individuals with disabilities, and young adults. They also allow homeowners to generate rental income or sell ADUs as condominiums, enhancing financial flexibility.
Ordinance 25-014 responds to Washington State’s legislative push to address the housing affordability crisis, particularly through bills like Engrossed Substitute Senate Bill 6617 (2020), Engrossed Substitute Senate Bill 5235 (2021), and House Bill 1337 (2023). These laws mandate counties to update ADU regulations, remove owner-occupancy requirements, and allow new ADU configurations in urban zones. The ordinance also aligns with the Puget Sound Regional Council’s Multicounty Planning Policies (MPPs) and Snohomish County’s Countywide Planning Policies (CPPs), which emphasize diverse, affordable, and accessible housing.
The ordinance supports GMA Goal 2 (reducing sprawl) by promoting infill development in urban growth areas (UGAs), thus preserving rural and resource lands. It also advances GMA Goal 4 (housing) by diversifying housing types and encouraging affordability for all economic segments. Additionally, it implements the 2020 Housing Affordability Regional Taskforce (HART) recommendation to revise zoning for ADUs, reinforcing Snohomish County’s commitment to equitable housing solutions.
The ordinance received strong community and professional support. During the March 19, 2025, public hearing, Council Chair Nate Nehring noted significant community interest, calling it “a great policy.” Natalie Reber from the Master Builders Association of King and Snohomish Counties praised the ordinance for aligning with the GMA and supporting housing affordability. The Snohomish County Planning Commission, after a public hearing on September 24, 2024, recommended adoption with additional amendments to increase lot coverage and reduce setbacks, which were incorporated into the final ordinance.
Council Vice Chair Megan Dunn emphasized the ordinance’s role in protecting open spaces through infill housing. “These regulations will allow more flexibility for infill housing in our urban areas to protect our open spaces,” Dunn said. “These small changes and code updates will have a big impact on our housing crisis and promoting all housing types for all types of families.”
Snohomish County, like much of Washington State, faces a severe housing affordability crisis and a shortage of housing stock. The median home price in the county has soared in recent years, making homeownership unattainable for many residents. ADUs offer a practical solution by providing smaller, more affordable housing options without requiring new land development. They are particularly valuable for seniors seeking to age in place, young adults entering the housing market, and families needing space for multigenerational living.
The ordinance’s focus on urban zones aligns with the county’s 2024 GMA Comprehensive Plan, which prioritizes compact, well-designed UGAs to accommodate population growth. By increasing residential capacity within existing urban areas, the ordinance reduces the need to expand UGA boundaries, preserving rural landscapes and supporting sustainable development.
For property owners, Ordinance 25-014 offers significant opportunities:
For renters, ADUs provide access to affordable, well-located housing near jobs and transportation. Their smaller size and lower construction costs often translate to below-market rents, making them an attractive option for low- and moderate-income households.
While the ordinance is a significant step forward, implementing ADU expansion comes with challenges. Property owners must ensure compliance with water and septic system requirements, as outlined in SCC 30.28.010, which may involve costly upgrades. Additionally, while setbacks and lot coverage rules have been relaxed, navigating zoning and permitting processes can still be complex. The county’s Planning and Development Services Department will play a critical role in streamlining approvals and providing guidance to homeowners.
Community concerns about increased density, parking, and neighborhood aesthetics may also arise. However, the ordinance’s alignment with state laws and its focus on urban infill helps address these concerns by concentrating development in areas already designed for higher density.
For homeowners interested in building an ADU, here are key steps to consider:
Snohomish County’s Ordinance 25-014 marks a pivotal moment in addressing the region’s housing affordability crisis. By expanding ADU permissions, removing restrictive regulations, and aligning with state and regional housing goals, the county is paving the way for more diverse, accessible, and sustainable housing options. Whether you’re a homeowner looking to add value to your property or a renter seeking affordable housing, this ordinance opens new doors in Snohomish County. As Council Vice Chair Megan Dunn noted, these changes are a small but impactful step toward solving the housing crisis and fostering inclusive communities.
For more information on ADU regulations or to start the permitting process, visit the Snohomish County Planning and Development Services website or contact their office directly.
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