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Book a callIn the vibrant city of Seattle, homeowners are looking at innovative ways to leverage their property to meet personal and community housing needs. Accessory Dwelling Units (ADUs) and Backyard Homes, also known as Detached Accessory Dwelling Units (DADUs), offer a compelling solution. But what does the legal landscape look like for these potential additions? Here’s the ultimate guide to understanding ADUs and Backyard Homes in Seattle.
ADUs and DADUs represent a modern approach to urban living, providing homeowners the opportunity to maximize their property's potential. Whether it’s converting a basement into an in-law apartment (an ADU) or building a cottage in your backyard (a DADU), these units can add value in multiple ways. Contact Our Experts
Seattle's Accessory Dwelling Unit (ADU) Regulations for Neighborhood Residential Zones
Seattle allows accessory dwelling units (ADUs) in its Neighborhood Residential 3 (NR3), Neighborhood Residential 2 (NR2), and Neighborhood Residential 1 (NR1) zones. These zones were formerly known as Single Family zones before being renamed in 2022. The key standards for ADUs in these zones are as follows:
- Lots in NR3, NR2, and NR1 zones can have up to two ADUs.
- The city distinguishes between attached ADUs (AADUs, such as basement suites or in-law apartments) and detached ADUs (DADUs, often called backyard cottages).
- If a lot has two ADUs, only one can be a DADU.
- Both AADUs and DADUs have a maximum size limit of 1,000 square feet of gross floor area.
- Certain areas like garage space, storage, underground levels, and small porches/decks are excluded from this calculation.
- To construct a new DADU, the lot must be at least 3,200 square feet in area.
- DADUs require a minimum lot width of 25 feet and depth of 70 feet.
- There are limits on the percentage of the lot that can be covered by structures (lot coverage) and the percentage of the rear yard that can be occupied by accessory structures like DADUs (rear yard coverage).
- ADUs must generally be located outside the required front yard and side yards.
- Minimum yard setbacks are specified for the front, rear, and sides.
- Maximum height for DADUs depends on the lot width, with a base height limit and additional allowance for different roof types.
- Floor area in ADUs is exempt from FAR calculations in these zones.
- Off-street parking is not required for ADUs.
This covers the key ADU standards for NR3, NR2, and NR1 zones in Seattle. Regulations differ for Residential Small Lot (RSL) and Low rise Multifamily (LR) zones, which are discussed separately.
The 2019 legislation marked a turning point, significantly easing restrictions and actively encouraging the development of ADUs and DADUs. This legislation has led to a spike in permit applications, reflecting growing homeowner interest in exploring these options.
Accessory Dwelling Units (ADUs) offer several advantages for communities and homeowners in Seattle. By permitting the construction of additional small living units on existing single-family lots, ADUs can help address housing needs while maintaining neighborhood character. Some key benefits include:
ADUs increase the diversity of housing choices within residential neighborhoods. Backyard cottages (detached ADUs or DADUs) in particular provide an affordable alternative to traditional single-family homes, thanks to their smaller footprints and reduced land costs. This allows for more economic integration in areas that may otherwise be out of reach for moderate-income renters or buyers.
Both attached and detached ADUs accommodate a range of living situations. They can meet the needs of multi-generational households, allowing extended families to live together while maintaining some independence. ADUs also work well for families looking to create supplementary living space as their needs evolve over time.
With an ADU, homeowners can generate rental income by housing tenants in the additional unit. This income stream can help owners better afford their mortgage, cover home maintenance costs, or simply provide supplemental revenue to remain in their neighborhood as housing costs rise.
By enabling modest density increases within established neighborhoods, ADUs represent a form of sustainable infill development. They make use of existing infrastructure and services rather than promoting suburban sprawl. The incremental densification from scattered ADUs can reduce development pressures on undeveloped lands.
When properly regulated for aesthetics and scale, DADUs blend well into single-family communities by mimicking traditional accessory structures like garage apartments or carriage houses. This allows neighborhoods to gently increase housing capacity while retaining their fundamental character and low-rise nature.
These units promote denser living within existing neighborhoods, reducing urban sprawl and its associated environmental impact. They also foster a sense of community by integrating diverse living spaces.
In summary, allowing ADUs provides homeowners flexibility, creates more affordable rental options, supports sustainable land use patterns, and facilitates a mix of housing types attuned to diverse household needs and demographic trends.
- In Neighborhood Residential (NR) and Residential Small Lot (RSL) zones: Up to 1,000 sqft
- In Lowrise Multifamily (LR) zones: Up to 650 sqft
- Must meet all Seattle residential construction codes for things like structure, electrical, mechanical systems, land use, environmentally critical areas, and shoreline regulations - just like a regular house.
- In NR zones, minimum lot size of 3,200 sqft is required to build a new DADU
- In NR and RSL zones: Up to 1,000 sqft
- In LR zones: Up to 650 sqft
- Must follow the same construction codes and regulations that apply to single-family homes in Seattle, covering structural, mechanical, electrical, energy efficiency, land use, critical areas, etc.
Seattle allows a range of manufactured/prefab home options for building DADUs from various approved builders.
The key things to remember are the maximum size limits based on the zoning, the minimum lot size for new detached units in residential areas, and that all ADUs must fully comply with the city's residential construction standards. Contact Our Experts if you need any clarification or have additional questions!
Navigating the permitting process can be complex. Homeowners must comply with current Seattle codes covering residential, building, mechanical, electrical, energy, land use, and more.
Designing an ADU or DADU requires thoughtful planning to maximize space and efficiency while adhering to zoning and code requirements. Costs can vary widely based on size, materials, and labor.
Success stories abound in Seattle, with homeowners transforming their properties in creative ways to accommodate ADUs and DADUs, proving the feasibility and benefits of these units.
For Seattle homeowners curious about ADUs and DADUs, there’s never been a better time to explore your options. With supportive regulations and a clear demand for more diverse housing options, adding an ADU or DADU could be a smart investment in your property and community.
Are you considering an ADU or DADU? Start by researching specific requirements for your property and Contact Our Experts so they can guide you through the design and permitting process. For further resources and related articles, Seattle’s official websites and housing resources offer a wealth of information to get you started on this exciting journey.
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