Is Your Seattle Property Eligible for an ADU or DADU? Here’s What You Need to Know

Jun 11, 20200 comments

In 2019, Mayor Jenny Durkan and Seattle City Council passed legislation that included some new rules that made it easier to build ADUs (Accessory Dwelling Units)/DADUs (Detached ADU. Backyard cottages, as people affectionately call them, provide more density for the Seattle housing market without tearing old houses down. Proponents of loosening these regulations believe that encouraging homeowners to build ADUs will help increase affordable housing and rental units within the city.

If you have a home in Seattle and want to know more about ADUs, including whether your property is eligible, read on.

Related Article: Seattle Aims to Ease Building of Backyard Cottages

What Is an ADU/DADU?

ADU/DADU sounds like a complicated term, but it’s actually quite simple. An ADU is like a tiny home for your back yard. That is why many people call them “backyard cottages.”

Most ADUs are entirely self-sufficient. These are separate and fully self-sufficient units. These units have a working kitchen, restroom, living space, and a bedroom (or, in the case of a studio floor plan, the bedroom is not distinct). They also have separate heating, cooling (if necessary), plumbing, and electricity.

An Attached Accessory Dwelling Unit (AADU) is attached to the main home, usually above or below. The most common are basement apartment units. These are often self-sufficient suites meant for relatives to stay and have privacy, but not have the structure detached. For example, some people use these to care for aging parents. A Detached Acessory Dwelling Unit (DADU), as you might guess, is disconnected, and it is a separate home located on the same lot. DADUs are only allowed in the backyard, not the front.

Why Build An ADU?

Homeowners may want to add an ADU/DADU to their property for a variety of reasons. If people put ADUs in their back yard and rent them out, it becomes an income stream for the homeowner, extra space for someone who wants to move to Seattle (and there are a lot of people who want to do that), and additional revenue for the city. Many jurisdictions, including California, have relaxed laws on ADUs for these same reasons.

How Have Seattle Laws Changed?

In July 2019, Seattle City Council, led by Mayor Jenny Durkan, passed reforms for ADU laws, which took effect on August 8, 2019. Specifically, these reforms include:

  • Allowing up to two ADUs on one lot (2 AADU’s or an AADU and a DADU)
  • Allowing ADUs on smaller lots
  • Not requiring owners to live in the primary residence to build and have an ADU
  • No longer requiring off-street parking for an ADU (as Seattleites know, having extra parking for an ADU is a challenging requirement to meet)
  • Increasing the size limit to 1,000 square feet for a detached ADU (note that if you build your ADU over your garage, the space over your garage does not count towards this limit)

Additionally, this legislation introduces the novel concept of a “pre-approved” ADU. Essentially, this designation provides homeowners with the ability to select plans and designs that the City Council has already vetted. By selecting one of these ADUs, you can have confidence that your project will receive streamlined approval.

The idea behind these reforms was to “remove regulatory barriers and make it easier for property owners to create accessory dwelling units (ADUs) in Seattle’s single-family zones.”

Is Your Property Eligible for an ADU?

Whether or not your property is eligible depends on a few factors. You’ll have to meet these essential criteria to have an ADU on your property:

  • 3,200 square foot minimum lot size
  • 25-foot lot width
  • 70-foot lot depth

ADU Lot size (1)

  • The number of residents in the ADU and primary house must not exceed eight (unless everyone is related to each other)
  • While you do not need to add parking for your ADU now, you also cannot build your ADU and remove existing required off-street parking, unless you replace it with some other parking spot on your property

ADU residents and parking

  • Your ADU cannot exceed 60% of your rear yard (if putting your ADU would remove trees, it cannot cover more than 40% of the yard)

ADU rear lot and size limits

As long as you meet those basic requirements, there’s a decent chance that you will be able to build some form of ADU. Like most bureaucratic endeavors, there are some other eligibility requirements, as well.

Unfortunately, there isn’t a way online to check if your property is eligible. You’d have to start with your lot size, including how wide and long it is. The next step would be to get in touch with a designer or choose from a pre-approved plan that would work for your particular lot.

Check your lot size and zoning on Seattle’s GIS Map.

Explore If an ADU Is Right for You!

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These changes make ADUs much more accessible for the average homeowner. Whether you want to rent it out or move aging family members close by, you should consider these changes that streamline the process. It’s a worthwhile investment that will undoubtedly pay off for years to come!

Further Resources:

City of Seattle ADU PDF
City of Seattle DADU PDF
New ADU rules drops barriers to building – CURBED

About Beachworks

Beachworks LLC local, family-owned company in north Seattle committed to improving the value of our community. For those who need to sell their homes quickly and privately, we we provide an all cash offer and close on your timeline.

Is Your Seattle Property Eligible for an ADU or DADU? Here’s What You Need to Know
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Is Your Seattle Property Eligible for an ADU or DADU? Here’s What You Need to Know
The building process for accessory dwelling units was recently streamlined in Seattle. Here's all you need to know about why you should build one and whether you are allowed to.
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