The City Council has just voted to update the Seattle Land Use Code, making it even easier to build ADUs in the city. Changes include: allowing bigger cottages (1000 s.f., up from 800 s.f.), removing the owner-occupancy requirement, removing the parking requirement, and even allowing more than one ADU on a lot.

With Backyard Cottages / ADUs in the news, I thought I’d explain a little what ADUs etc. are, and show examples of different configurations.

ADU stands for Accessory Dwelling Unit, and can refer generally to any additional living unit, or more specifically to an attached unit within an existing main residence (for example a basement apartment). An ADU can also be called a Mother-in-Law Apartment.

DADU stands for Detached Accessory Dwelling Unit, and refers to a stand-alone structure, usually in the back yard, separate from the main residence. A DADU can also be called a Backyard Cottage.

A Carriage House is a DADU that contains a garage within the same structure.

We have done many ADUs, both attached and detached. Here are some examples:


West Seattle Backyard Cottage
built 2012, 315 s.f.
This very small cottage serves as a backyard office for the homeowners and a guest cottage for visitors. It’s a studio configuration, with a pull-out couch in the living space, and a small kitchenette.














Phinney Ridge Carriage House
built 2014, area: upper living unit 298 s.f., garage 375 s.f.
This is a new office/guest studio built over an existing garage. The garage was structurally upgraded to support the new second story, which is accessed by new exterior stairs. The carriage house was designed to match the traditional main house.
















Green Lake Backyard Cottage
built 2012, area: 792 s.f. (main floor 540 s.f., upper 252 s.f.)
This is a story-and-a-half, 2 bedroom, 2 bath backyard cottage in the Green Lake neighborhood. The owners wanted a detached accessory dwelling unit that, in the short term, will provide a place for the in-laws to stay during extended visits. In the long term, it will act as a residence for the in-laws when they re-locate here. The ground floor bedroom can be accessed separately from the DADU, to act as a guest bedroom for the main residence. This DADU was just under the former size limit (800 s.f.)















Northgate Backyard Cottage
built 2018, area: 499 s.f.
This one-bedroom DADU was designed as a separate residence for an Au Pair, to take care of the owners’ children.















View Ridge ADU
built 2010, area: 1044 s.f.
This basement ADU was part of a whole-house remodel that completely re-configured the house inside and out, including a new roof deck and solar array. The ADU contains several interesting features, including in-wall radiant heat, and a glass floor that allows the ADU to borrow natural light from the main residence’s well-lit atrium space above. Incidentally, this was over the nominal limit of 1000 s.f., but the code allowed an exception in older houses under certain conditions.