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Laneways Around the World: Seattle



Image from: seattle.gov


In the third part of our series in exploring various Laneway Suites across the globe, we will be observing Seattle as a case study to better understand the differences in comparison to Toronto.


Seattle is another city in the United States to consider and legally pass the construction of backyard housing units. Back lane housing, also often referred to as granny flats, infill housing, coach houses, or accessory units, has been adopted as a new way of providing space in single-family areas that have the intention of renting the added space on their own property.


The purpose of backyard units and introducing a mix of housing types, especially in Seattle, is to address the issue of affordable housing. In 2016, the Seattle City Council published a proposal that would simplify the process for more homeowners to build backyard cottages and basement units, thus providing more housing options for Seattle renters.

The objective of Seattle's vision for ADUs was a way to address the pre-existing Land Use Code, which also included:

  • increase ADU production to grow the volume and variety of housing choices available in single-family zones;

  • support lower- and middle-income homeowners in developing ADUs; and

  • increase access to ADUs for lower-income renters.

Growing the number of Accessory Dwelling Units (ADUs) in single-family zones is part of addressing Seattle’s housing affordability crisis. ADUs comprise both backyard cottages or Detached Accessory Dwelling Units (DADUs), in-law or basement apartments or Attached Accessory Dwelling Units (AADUs). ADUs have the possibility to offer new housing opportunities in neighborhoods and regions where single-family homes are often too costly for many people; If just 5% of eligible lots in the city build ADUs, it would create approximately 4,000 housing units.


Later in 2016, based on a decision from the City’s Hearing Examiner, the Council was required to provide an Environmental Impact Statement (EIS) describing potential environmental impacts of proposed changes to the Land Use Code intended to remove barriers to building ADUs. In October of 2018, the Final EIS was published which identified potential environmental impacts of the proposed code changes and would be informed. The presented alternatives described in the EIS have become the basis for legislation moving forward.


As of July 2019, the current guidelines include:

  • Reduce the minimum lot size required to build a DADU on a single-family lot from 4,000 square feet to 3,200 square feet;

  • Increase the maximum size of DADUs from 800 square feet to 1,000 square feet, excluding any parking or storage areas;

  • Removes the owner-occupancy requirement for ADUs;

  • Removes the off-street parking requirement for ADUs;

  • Allows two ADUs on one lot (either one attached and one detached, or two attached) if the second ADU meets a green building standard or will be affordable to households at or below 80% of area median income;

  • Increases the maximum household size permitted on a single-family lot from 8 to 12 unrelated people only if the lot includes two ADUs;

  • Increases DADU height limits by 1-3 feet, with flexibility for green building strategies;

  • Allows design flexibility to preserve existing trees and to convert existing accessory structures to a DADU;

  • Require annual reporting on ADU production and require that the Office of Planning and Community Development and the Seattle Department of Construction and Inspections conduct a survey of ADU owners and occupants within 3 years.

  • Introduces a Floor Area Limit (FAR) for all new development in single-family zones with some exemptions (this regulation has a delayed effective date until March 1, 2020)


Additionally, the Office of Seattle conducted a Racial Equity Toolkit (RET) to evaluate the racial equity impacts of proposed policies, programs, and investments. The analysis completed for the RET emphasized that Land Use Code changes alone are inadequate to address racial disparities that have resulted from a history of race and class-based planning and housing policies. The office developed additional methods to address this issue, which include:

  • Support low-income homeowners and homeowners who are people of color to stay in their communities—with tools to help leverage the value of their property without selling, by creating additional living space or ADUs for family members, or to generate rental income.

  • Make rent and income-restricted ADUs so low-income households can benefit from new housing opportunities in single-family zones.

  • Pilot program to create more habitable space

  • Bring awareness about community outreach resources and programs that would help eligible homeowners with participating in the ADU initiative.

  • Urban Sustainability Accelerator, a year-long ‘cohort’ of city and county teams from across the country working to promote ADUs. The team's work will focus on programmatic ideas that align with addressing the challenges we hear from homeowners and will prioritize programs that further racial equity.


Seattle is a relevant example of how a new method of housing can allow easier access to living in single-family areas. Additionally, the city conducted in-depth research of the program’s impact on the environment, as well as accessibility to low-income and minority homeowners to participate within the new housing movement. The ADUs illustrates the high demand for providing more affordable housing and an efficient way of enriching neighbourhoods of all statuses.


If you are interested in Garden/Laneway Suites or have any further questions, please send us an email or book a meeting.


Sources: seattle.gov


Lawn Strip

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