What does the new ADU legislation mean for you? / by Atelier Drome

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On July 1, the Seattle City Council voted to pass new code legislation regarding accessory dwelling units (ADUs.)  ADUs are a great way to increase density into single family zones (SF zones) in a manner that respects the scale of the neighborhood.  There are two types of accessory units, detached and attached.  Detached units are those that are separated from the main house.  It could be in an unit above a garage or a small cottage in a backyard.  Attached units are part of the main home and are most commonly found as a basement apartment.  Many homeowners use these units as a way to provide housing for extended family members or to create extra income by renting out the unit. 

The goal of the legislation was to make it easier for homeowners to add ADUs to their homes in SF zones.  Homeowners can now have (2) units, either (2) attached or (1) attached and (1) detached, and are no longer required to provide parking for the units.  With these changes, in addition to removing the owner occupancy requirement and adjusting several of the development standards, the legislation does succeed.  

Homeowners can now have (2) units, either (2) attached or (1) attached and (1) detached, and are no longer required to provide parking for the units.

However, the changes also introduce a new challenge for homeowners who are looking to build a new home or make changes to their current one. The amount you are allowed to build will now also depend on the size of your lot, in addition to the required setbacks and lot coverage already in the current code.  The legislation incorporates square footage restrictions to single family zoning by adding a floor area ratio (FAR) limit.  FAR is already used in multi-family zones and is essentially the interior square footage of your home. 

For example, if your lot is 5,000 sf, you can only build up to 2,500 sf of FAR or roughly 2,700 sf in real estate terms.  There is an one-time exemption for homeowners whose current home exceeds the allowable FAR but would like to add onto their home.  In these cases, you can add up to 20% of the area of your current home. 

The majority of the changes will be in effect 30 days after the Mayor signs the bill, likely early August, but the size limitations won’t go into effect until March 1, 2020.  As many of our projects focus on home additions, remodels, and accessory units, our team has been following these changes closely.  If you are thinking of adding an accessory unit or make changes to your current home and have questions, please feel free to reach out to us with any questions!  


Written by Molly O’Donnell, ATELIER DROME architecture + interior design