Proposed DADU/ ADU Code changes create new possibilities for your home!

If you are thinking of constructing an attached accessory dwelling unit (ADU) or a detached accessory dwelling unit (DADU), you will find the proposed land use code changes explained in the Seattle City Council report “Removing Barriers to Backyard Cottages & Accessory Dwelling Units” useful.  By the way, DADUs are also known as backyard cottages, mother-in-law units or carriage houses.

Here are a few of the proposed changes that may increase feasibility for adding another dwelling to your property.  One is to expand the allowed DADU size so that it matches the allowed ADU size, which is 1000 square feet of gross floor area.  Another is to let backyard cottages be slightly taller and also to not count interior parking and storage as part of the allowed gross floor area.  These changes will have a big impact on your ability to convert existing structures, such as garages, to DADUs.


Another change is to allow the minimum lot size for a DADU to be slightly smaller–3200 square feet instead of 4000 square feet, which will open up this possibility for more people.  The new changes remove the additional parking space requirement.  Often adding a parking space to the property is challenging, and simply privatizes a street parking space by adding a curb cut.

We are looking forward to the next steps for implementing these code changes.  We’re tracking the legislative process and will add updates to this blog!

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