Case Study: DADU as a Primary Dwelling

Seattle is in the middle of a long running debate on DADUs. For those who are not up on your land use acronyms, DADU stands for ‘detached accessory dwelling unit’, often called backyard cottages, granny flats or in some cases, alley flats. While we think the benefits of DADUs are self-evident, not everyone agrees with us. So, in the interest of adding some information to the debate, we are going to present a couple of case studies of different ways a DADU can be designed and used to hopefully illustrate how useful DADUs are as a tool for adding density while preserving ‘character’ and ‘livability’. The quotes on those last two words are there for a reason but I am going to save that for another post.

The project we are showing here is a DADU designed to be a primary dwelling which is not how many people think of them. With the word ‘accessory’ in the name, DADUs are primarily thought of as the secondary structure on the lot. In this case, the clients will be using the new DADU as their home and renting out the existing single-family house on the lot for rental income, reversing that idea.

The clients are a middle age couple with no kids, although they do have a child sized dog. Their previous homes in Seattle have been a 900 sqft townhome and a 3,000 sqft single family home so they have explored the size ranges thoroughly. They purchased a home in the Central District with an eye toward building a DADU in the rear of the lot to serve as their home. The challenge was how to design a home that was no larger than 800 sqft that would feel ample enough to truly be a forever home.

The DADU is a L shaped plan that creates a courtyard accessible from both the living area and the bedroom. Large sliding glass doors allow the living area to ‘steal’ the outside and appear much larger than it actually is. We designed the home to be on one level, both for aging in place needs as well as to allow us to have higher ceilings which create a more spacious feel. As the entry is from the alley, we created an entry courtyard to extend and soften the entry sequence. The garage serves as object implying the edge of the courtyard and creating an outdoor room as well as providing space for outdoor gear and the other parts of life that don’t fit into 800 sqft.

Seattle Backyard Cottage

So what are the benefits of this approach?

  • It adds much needed density to Seattle single family zones. This lot now has two families on it as opposed to one. Lot efficiency doubled.
  • By placing a second structure on the site, we prevent the existing house being torn down and replaced with a lot maximizing Mcmansion. A small blow for affordability.
  • The new structure will activate the alley.

What were the challenges:

  • Funding: Banks are reluctant to lend on an asset they cannot sell. Seattle prohibits selling off a DADU independent of the main house due to ownership restrictions which makes obtaining a traditional construction loan on DADU's almost impossible. If the clients had not been selling a much larger house, they would not have been able to make this work. Removing the owner occupancy restriction would help with this.
  • Size: 800 sqft is tight. It worked for this couple but it would be challenging for a family with kids. A couple hundred more square feet would help.

For our next round, we are going to look at a more traditional setup where a DADU allows an extended family to live together yet maintain separate homes. Stay tuned.

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