Backyard Cottages

Zoning Changes for Backyard Cottages & Mother-in-Law Apartments

The City of Seattle has allowed backyard cottages (Detached Accessory Dwelling Units or DADUs) since 2010, and mother-in-law apartments (Attached Dwelling Units or ADUs) for more than a decade in all single-family residential zones.  In September 2014, the City Council adopted Resolution 31547 to explore policy changes for increasing the number of these units.  In July 2015, the Housing Affordability and Livability (HALA) Report made a similar recommendation.  The Seattle Planning Commission (SPC) submitted their recommendations to the City Council in a letter dated March 31, 2016, and legislation is expected to move forward soon in the City Council.

The WallHALA committee of the Wallingford Community Council encourages backyard cottages associated with owner-occupied homes in ways that increase affordable housing and contribute to the stability and well-being of the neighborhood. It is better we buy houses atlanta as it sounds a good option for settling down in a new environment.

The present law governing backyard cottages was carefully designed to mitigate impacts to neighborhoods and adjacent lots.  Since the program began as a pilot program in 2009, about 30 cottages have been built each year, with an average lot size of 6770 square feet.  Forty-two percent of these units are on alleys, which mitigates the impacts on neighboring lots. Only a portion of backyard cottages are rentals.

After reviewing the City’s proposals, the WallHALA committee has identified the following concerns with these proposed changes to the current regulations.

Owner Occupancy

Proposed Change: Remove the Owner-occupancy Requirement

Currently:  The owner must live on the premises six months of the year (allowances can be made for longer absences.)

The City’s proposal to remove the owner-occupancy requirement increases the likelihood of potential livability issues typically associated with absentee landlords, such excessive noise, trash, and lack of maintenance.  Removing the owner-occupancy requirement could also lead to speculation.  If developers are encouraged to speculate based on the ability to develop two or more dwellings on one lot, then the price of single family properties will rise.

Backyard Cottages and Mother-in-Law Apartments (DADU and ADU)

Proposed Change: Allow Both a Backyard Cottage and a Mother-in-Law Apartment

Currently: Either type of accessory unit may be built, but not both on the same lot.

Proposed change would allow both a backyard cottage and a mother-in-law apartment, on the same lot as the principal dwelling.  This would be three separate dwelling units on a single family lot.  There has been much debate as to whether or not this is a backdoor to rezoning of single family zones.  Most of the backyard cottage proposals are conceived as ways to remove barriers to construction, but this proposal is geared towards commercial development of multi-unit rental properties that would be very different in purpose from the backyard cottages on owner-occupied lots being built today.


Proposed Change: Remove the Requirement for an Off-Street Parking Space

Currently: One off-street parking space is required for an accessory unit in addition to one off-street parking space for the principal dwelling unit in single family zones.  There is no parking required for new construction in any zone inside urban villages or centers, including in the Wallingford Residential Urban Village. You can also read about Wapiti Pacific Contractors as they can help in matters related to construction.

Proposed change is to remove the requirement for an additional off-street parking space for an accessory unit or backyard cottage.  Seattle lacks an alternative for easily and cheaply getting around without cars.  Many single family houses in older neighborhoods were built without off-street parking.  Many neighborhoods already have more cars than there is available on-street parking.

The working poor, who rely on personal vehicles to reach multiple jobs, will suffer most from a lack of parking.  Additionally, locally-owned small businesses rely on on-street parking for their customers.  A lack of on-street parking also creates difficulty for the handicapped, the elderly, people with children, and more.

Alternative proposal: Require one off-street parking place for each unit, including in urban villages.

Maximum Unrelated Persons

Proposed Change: Increase Density of Unrelated Persons (Household Size)

Currently:  A maximum of eight unrelated persons may reside on a single family lot.

Proposed change would allow up to 12 unrelated persons on a single family lot.  This makes it possible to turn a single family home with an ADU or a DADU into the equivalent of a dormitory or “apodment” with up to 12 separately rented units. This is more likely to occur in neighborhoods like Wallingford near major institutions, especially if the owner occupancy requirement is removed.  The neighborhood could be impacted by large numbers of cars competing for limited on-street parking.

Minimum Lot Size and Lot Coverage

Proposed Changes: Reduce Minimum Lot Size and Increase Maximum Coverage Limit

Currently: The minimum lot size for building a backyard cottage is 4000 square feet.  Lots under this size are found primarily in neighborhoods with some of the earliest platting, such as Wallingford, Queen Anne, and the Central Area.

Lots of 5000 square feet and larger are allowed 35% lot coverage (by buildings).  Lots less than 5000 square feet are allowed 40% lot coverage.

The proposal to reduce minimum lot size to 3500 square feet could result in lots with buildings crowded together and the loss of privacy for neighboring lots.

The Seattle Planning Commission (SPC) has proposed to allow a garage or storage area not to be counted in the total square footage allowance for the accessory dwelling unit.  Additionally, the SPC recommends increasing the maximum square footage of a DADU from 800 square feet to 1000 square feet and allow “for a DADU, combined with other accessory structures such as a garage or shed, to cover slightly more than 40% of a rear yard.”  The combination will result in greater lot coverage and larger footprints for backyard cottages – and works against affordability, since smaller dwellings cost less.

Due to the adoption of the “Green Factor” requirements in commercial (mixed use) and multi-family zones, new development is no longer required to plant new trees or to maintain existing trees when lots are redeveloped.  As a result, Seattle’s tree canopy is now decreasing.  The Mayor’s proposed Comprehensive Plan predicts a further loss of tree canopy.  A significant portion of Seattle’s tree canopy exists on single family lots, and the majority of large trees are located in backyards.  With the proposed changes, the amount of lot coverage by buildings increases and the allowable lot sizes for backyard cottages decreases.  The result will be a significant loss of tree canopy throughout the city.

Note: Minimum lot sizes for backyard cottages in other cities are 5000 square feet in Santa Cruz CA, 6000 square feet in Boulder CO, 6000 to 8500 square feet in Denver CO, and 10000 square feet in Lexington MA.

Alternate Solution: A preferred solution would allow backyard cottages on lots of less than 5000 square feet only on corner lots or on lots with alleys.

Heights and Setbacks

Proposed Changes: Increase Height Limits and Reduce Setbacks

Currently:  Building heights are based on the width of the lot, a nuanced approach that recognizes the potential of height to impact adjacent neighbors.

Proposed changes to the height limits are shown in the table below as bold:

Lot Width Base Height Pitched Roof Height Shed/Butterfly Roof Height
< 30 feet 12 feet 15 feet 15 feet
30 to 35 feet 14 feet 21 feet 18 feet
35 to 40 feet 15 feet 22 feet 19 feet
40 to 50 feet (present) 16 feet 22 feet 20 feet
40 to 50 feet (proposed)
(with rear lot line on alley)
18 feet
20 feet
24 feet
27 feet*
22 feet
24 feet
> 50 feet (present) 16 feet 23 feet 20 feet
> 50 feet (proposed) 20 feet 27 feet* 24 feet

*27 feet would allow for a three-story structure, assuming the third floor had sloped ceilings.

The proposed height increases could create a “looming effect” with additional shading and loss of privacy on neighboring lots.

Currently: The current setbacks are 5 feet from the property line, except for entrances, which require a 10 foot setback.

The proposal is to decrease the setback for entrances from 10 feet to 5 feet, when the entrance faces a neighboring lot.  This will reduce privacy on neighboring lots.

Alternate Solution: A preferred solution would limit Base Height depending on lot line setbacks (in addition to the above limits).  For a 40-50 foot wide lot, the Base Height would be 16 feet with a 5 foot setback. Portions of the building above 16 feet would be required to be setback an additional 2 feet for each additional one foot in height.  (Example: Adding an additional 2 feet in height for a total of 18 feet would require a 9 foot setback.)

Cumulative Impacts

General concerns regarding the combination of proposed changes

The 2010 Multi-family code revisions created what the author, former Councilmember Sally Clark, called “unanticipated problems” when developers combined multiple new exceptions written into the code.  The cumulative effects of combining the proposed changes to backyard cottages could create an entirely new housing form in single family zones.

The HALA Strategy SF.2 proposes allowing more variety of housing types in single family zones, including duplexes and triplexes.  By allowing a principal dwelling and an ADU and a DADU on a single family lot, this proposal moves towards the HALA goal of allowing multi-family dwellings on single family lots.

If the owner occupancy requirement is removed, and both an ADU and a DADU are allowed on the same lot, there is a strong potential for three-unit rental properties in single family zones.

Allowing a principal dwelling and an ADU and a DADU, plus non-owner occupancy, plus up to 12 unrelated occupants, plus no parking, would make it possible to create 12-unit rental compounds with no parking.  This result in no way resembles the current backyard cottage legislation, and increases the likelihood of investor speculation that will raise the purchase price for single family homes.


The case for affordability has not been made.  Only a fraction of cottages are actually rented.  Eliminating owner occupancy may lead to short term rental compounds, which reduce the supply of long term rental housing.  The comments by the researcher who wrote the report for the City concluded that those building DADUs were not motivated by a return on investment.  The City’s claim that the presence of backyard cottages will make it possible for people to afford to buy a home are not supported by any economic model.  Adding a backyard cottage would only increase the down payment and purchase price of a house.

Short Term “Hospitality” Rentals

Short-term rentals (like Airbnb and VRBO) work against the goals of housing availability and affordability.  This is a particular concern with proposals that support having dedicated rentals, such as removing the owner occupancy requirement and allowing both an ADU and a DADU.

Points of Agreement

Opinions vary in our community about the concerns listed above, but we think most would agree with the following Seattle Planning Commission’s recommendations to provide:

  • A step-by-step guide to the permitting process for a backyard cottage.
  • A database or clearinghouse of other mother-in-law/ backyard cottage owners, architects, and builders with previous experience with backyard cottages.
  • Pre-approved designs and plans for a variety of backyard cottages and different lot sizes that would help to speed up the permitting process.

Please contact the City Council with your concerns:

Lisa Herbold
Bruce Harrell
Kshama Sawant
Rob Johnson
Debora Juarez
Mike O’Brien
Sally Bagshaw
Tim Burgess
Lorena González


The Backyard Cottages page of Seattle City Councilmember Mike O’Brien, accessed 2016-04-25:

“Removing Barriers to Backyard Cottages” Report and Analysis by the Department of Planning and Development (DPD) of the City of Seattle, 2015-10:

“Seattle Housing Affordability and Livability Agenda”; Final Advisory Committee Recommendations, 2015-07-13:

“Removing Barriers to Backyard Cottages” letter by Seattle Planning Commission of the City of Seattle, 2016-03-31:

Share Button