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Backyard Cottage Illustrations | City of SeattleIllustrations: City of Seattle

Who is this guide for?

Hello there, and welcome to this info page about all things related to backyard cottages and in-law apartments in Seattle. We put this guide together for you, the Seattle homeowner interested in learning more about building a cottage in your backyard or an apartment in your basement. Perhaps you want some rental income or just have some extra space. If so, a backyard cottage or ADU can be a great choice, but the regulations can be a bit confusing, and Seattle is in the midst of changing them. There's probably more information here than you can take in, but we hope you can use it to get ideas and get started on your backyard cottage project. If there's anything you think should be included in this guide, we'd love to hear about it. You can email eric@crddesignbuild.com. Be sure to check back frequently or sign up for updates because we'll be adding new information as it becomes available.

What is an in-law apartment?

Sometimes called “mother-in-law apartments,” accessory dwelling units, or ADUs, these are self-contained living spaces built into your home. To create these apartments, you can convert your basement by adding an outside entrance, egress windows, and a small kitchen, or you can add on to the back or side of your home.  To be official, an ADU must have its own private entrance and meet certain other requirements.

Backyard Cottage | City of SeattleWhat is a backyard cottage?

Detached accessory dwelling units, or DADUs,  are small, standalone houses built behind your main home. They allow you to maintain your privacy and all the square footage in your main house while creating   extra living space. DADUs are  also known as "backyard cottages." Homeowners often opt to build these over a garage.

What are the benefits of backyard cottages?

There are many benefits to building these units alongside an existing single-family home or townhome. 

  • Backyard cottages provide many of the benefits of single-family homes, with no shared walls and a lower-density-neighborhood lifestyle.
  • They can promote economic diversity in neighborhoods that might be out of range for average-income renters.
  • ADUs and DADUs can provide passive rental income for the homeowner. This can help homeowners of modest means stay in their homes or simply put extra cash in your pocket to help pay the mortgage or pay for home improvements.
  • DADUs are an example of infill development, which slowly increases density and taking advantage of existing infrastructure. Both ADUs and DADUs can help reduce sprawl.
  • Seattle's population is growing due to the economic opportunity here, and we must increase our housing stock to keep pace. When compared to highrise developments, ADUs and DADUs are a solution that helps preserve the character of our beloved neighborhoods while empowering homeowners instead of large developers.

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Seattle Regulations

So you want to build a backyard cottage or ADU? Great! The first step is to make sure you know all the rules.   There are some major changes to the regulations in the works, but let's take a look at  the current regs. 

In-Law Apartments

Attached ADUs (in-law apartments) have been allowed in  all single-family homes in Seattle since 1994.  As of 2016, there are just over 1,000 units. Here is a rundown of the current ADU regulations:

  • Size limit: ADUs must be 1,000 square feet or under in a single-family home or 650 square feet and under in a rowhouse or townhouse.
  • Meet codes:   The ADU must meet current standards of the Seattle residential, building, mechanical, electrical, energy, land use, environmentally critical areas, and shorelines codes.
  • Parking: The homeowner must provide one off-street parking space for the ADU,   except for a rowhouse or townhouse in designated urban villages and urban centers and in lowrise zones.

Backyard Cottages

Backyard cottage regulations are more hotly contested and a bit more complicated than those for in-law apartments. The city started a pilot program in 2006, allowing DADUs to be built in Southeast Seattle. It was considered a success, and  the city expanded the program to include all of Seattle in 2009. However, as of 2016, only 221 backyard cottages have been built  out of the roughly 75,000 single-family lots that are eligible.

 

221 Existing DADUs in Seattle as of 2016                             75,000 Seattle Lots Are Currently Eligible for DADU Construction

Images:   www.seattle.gov/Documents/.../DADUCommunityMeetingboardsFeb2016.pdf

 

Current Backyard Cottage Requirements

If you're thinking about investing in a backyard cottage, you may want to check with a knowledgeable builder or architect about your eligibility or refer directly to  Seattle Municipal Code   23.44.016.D.8. Here is a summary of the current regulations:

  • Lot size: Your lot must be 4,000 square feet in a single-family zone. The city is not currently accepting variances for this requirement.
  • Cottage size: Only 800 square feet is allowed for DADUs in single-family zones and 650 square feet for units  in a lowrise zone. If your DADU incorporates a garage or storage area, that square footage counts toward your total.
  • Codes: As with any construction project, your backyard cottage must meet current  land use and building standards. No surprise here.
  • Parking: Just like for an ADU, you must be able  to create one off-street parking space for your new backyard cottage.

 Examples of site configurations for backyard cottagesSeattle City Council

Proposed Changes in Seattle Backyard Cottage Regulations

Back in  May of 2016, Councilmember Mike O'Brien proposed new regulations that would make it easier to build backyard cottages and in-law units in Seattle. Here is a rundown of the proposed changes:

  • Doubling up: Both an ADU and a DADU would be allowed on the same property. Currently, you can only have one or the other.
  • Height limit:   You could build a cottage up to 2 feet taller than current regs, depending on your lot width. Basically, this would make it more feasible for you to build a DADU with a second bedroom.
  • Parking:  The requirement for an off-street parking space would be removed for houses in many areas.
  • Lot coverage:  If your backyard cottage is only one story, it could cover 60% of the rear yard (up from 40%).
  • Owner occupancy: You would no longer be required to live on site in perpetuity, just for a year after the unit is created.
  • Lot size:  The required minimum lot size would drop  from 4,000 square feet to 3,200 square feet.
  • Floor area:  The max square footage of your cottage would increase from 800 to 1,000 square feet.
  • Garages exempt: If you build your DADU above a garage, the garage square footage would no longer count toward your total.

Current and Proposed Max Height Limits of Backyard Cottages in SeattleSeattle City Council

 

Current Status and Environmental Impact Statement Process

[From Seattle City Councilmember Mike O'Brien]

The Office of Planning and Community Development issued a State Environmental Policy Act (SEPA) Determination of Non-Significance (DNS) in May of 2016 on my proposal. Following the release, the Queen Anne Community Council appealed the DNS to the hearing examiner. This past December we received the response from the Hearing Examiner that reversed the DNS. After thorough examination of the Hearing Examiner’s response, we have decided to pursue a full environmental impact statement (EIS). This process will likely take a year to complete. The full EIS will enable us to look deeply into the potential environmental impacts of the proposed code changes and inform our proposal before we bring it to the Planning, Land Use and Zoning Committee.

There will be multiple opportunities for input during the EIS process. We will keep you informed of these opportunities for public comment and encourage you to engage. When the EIS is complete, we hope to bring legislation to committee by mid-2018.

I believe lowering the barriers to creating backyard cottages and in-law apartments is an important part of addressing affordability across the city, and am looking forward to continuing to pursue this legislation.

If you have further questions, please reach out to Susie Levy – susie.levy@seattle.gov or call our office at 206-684-8800.

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