You likely know them by several names – apartment over the garage, garage conversion, back yard cottage, granny flats or mother in law quarters.  In Portland, an Accessory Dwelling Unit is technically “any smaller, secondary dwelling unit which can be legally added either on the same lot or within a house, attached house or manufactured home in residential zones”.  Legally, an ADU is part of the same property as the main home.  It cannot (typically) be bought or sold separately.  What an ADU provides is a flexible living arrangement that can extend the value of a home.

Most people build an ADU on their property primarily to:
– expand living space for the family or extended family (ie. a place for mom to live so she can be nearby but not living in the room next door, or a place for the grown child to return to after college without having to be under the same roof).
– downsize to a smaller living space without giving up your property rights.
– have an office or studio workspace easily accessible and close to home.
– offset or pay for mortgage.  Some owners opt to remain in the house and use rental income from the ADU to help offset mortgage while others choose to move into the ADU and let the renter pay for most of or even the entire mortgage.

The true beauty is that an ADU can be all of these things at different times in its life span,  depending on the current needs of the homeowners.  We at zenbox design have been living/working in an ADU since 2013, and it has become the central point of our own “creative home use” plan.

zenbox design offers an onsite consultation for ADUs in Portland.
Contact us to set an appointment.




Note:  Portland ADU code changes (as of 12/2/15)
Portland City Council just approved several changes to the ADU zoning code, primarily making it easier to build small ADUs without some of the restrictions that previously applied.  See those changes updated/noted in bold below.



We are lucky enough to live in a city that has not only allowed for this type of flexible home use, but is actively supporting it as the type of growth encouraged in our communities.  The city of Portland is currently waiving System Development Charges (SDCs) on ADUs.  Meaning, if your ADU is built (application submitted before June 30, 2016 and occupied before June 30, 2017) all SDC charges can be waived.  For most homeowners this equates to a savings of somewhere between $10,000 and $15,000. 
EDIT:  City council just voted on a resolution that should extend the SDC fees waiver for another 2 years (through July 31, 2018)!  The resolution is set to be finalized before May 11, 2016.

The combined building coverage for all detached accessory structures may not exceed 15% of the total site area.  Detached ADUs must be set back 40 feet from a front lot line or directly behind the house.  ADUs must (typically) sit within the same side and rear setbacks as the primary home.  If the ADU is under 15′ in height it can sit within the typical side and rear setbacks.

ADUs under 15′ in height (and under 24′ in length) have no restrictions to match the house.  For those ADUs over 15′ in height some of the following apply:  
Exterior finish materials, roof pitch, trim, eaves, window orientation and dimension must be the same or visually match those of the house.

An ADU can be equal to 75% of the living area of the house or 800 sq. ft (whichever is smaller).

The maximum height for a detached ADU is 20 feet (on sloped roofs, maximum height is calculated to the midpoint of the slope).




2015 Portland ADU tour – If you are even considering an ADU project in the future, this event is a must!
Grandma Never had it so good – The NY Times article focused on 4 Portland ADUs including our own zenbox ADU
City of Portland – Bureau of Development Services ADUs Front Page
City of Portland – ADU Program Guide
AccessoryDwellings.org – A great all around resource for ADUs and examples ofexisting Portland ADUs


SDC Fees Waiver

The city of Portland is currently waiving the SDC (system development charges) Fees for ADUs built in Portland.  The waiver (which typically means a savings of $10-15k is currently set to expire in July of 2016 (being extended to July of 2018) .  If you are planning to build an ADU in Portland, we can help you figure out how to get approved before the deadline.

 Read More →

onsite consultation

zenbox design offers an onsite consultation for ADUs in Portland.  We will give you all the details related to the feasibility of your project; any limitations or hurdles you may face with the city because of your lot, location, existing structure or plans for the ADU and our recommendations for how to proceed.

Schedule an Appointment →