Affordability in housing is one of the biggest issues we face in Seattle today. The City of Seattle has identified the need for more housing at prices accessible to people at all levels of income, both for homeowners and renters.
Backyard cottages, or Detached Accessory Dwelling Units (DADUs,) have the potential to provide a significant amount of affordable housing.
If just 5% of eligible lots in the city build DADUs it would create about 4,000 housing units.
Backyard cottage owners love the extra space for personal use as well as the added financial boost.
In a recent survey of backyard cottage owners conducted by DPD, backyard cottage owners extol the additional space, which is ideal for family members, hosting guests, to use as a working space, and/or create long-term rental income.
There are relatively few backyard cottages in Seattle right now. The Seattle City Council is exploring a menu of options to make it easier for homeowners to build more of them.
DADUs have been allowed citywide since 2010. Since then, about 221 have been built. There are a menu of options that would make it easier to create more of them, such as changing regulations, creating preapproved permits and plans and implementing a waiver for permitting fees.
Proposal Encouraging Backyard Cottages and Mother-in-Law Units
Councilmember Mike O'Brien (District 6, Northwest Seattle) released a proposal on May 19, 2016 that would make it easier for more homeowners to build backyard cottages and mother-in-law units in Seattle. As the city faces an affordable housing crisis, Councilmember O'Brien developed the legislation to increase the housing supply by encouraging low-impact housing options that fit within the scale and character of Seattle's single-family neighborhoods.
Councilmember O'Brien's bill makes a series of changes to the existing backyard cottage and mother-in-law unit building code, including:
- Allowing both a backyard cottage and mother-in-law unit on the same property, which maintains the character and appearance of the property while providing an additional housing option.
- Increasing the height limit for backyard cottages by 1-2 feet, depending on lot width, which would create enough livable space to make two-bedroom units more feasible. Setback requirements from property edges would not change.
- Removing the requirement for owners to include an off-street parking space for backyard cottages or mother-in-law units, which prevents removal of green space on the property. Feedback found the parking requirement was prohibitive in creating new backyard cottages, as additional parking spaces were either unnecessary or unable to fit on the lot. For single-family lots outside urban villages or urban centers, the one parking space per house requirement will still apply.
- If a backyard cottage is only one-story, its floor area may cover up to 60% of the rear yard (currently 40%), creating a large enough livable space for those unable to use stairs. Existing setback requirements from the lot edge would not change.
- Requiring that the property owner live on-site for at least one year after a backyard cottage or mother-in-law unit is created, rather than the current requirement that the owner live on-site at least 6 months out of every year in perpetuity. The requirement prevents speculative developers from acquiring property and building backyard cottages that don't fit the character of the neighborhood, while allowing the owner future flexibility for those who don't want, or are unable to, continue living on-site.
- Allowing backyard cottages on lots 3,200 square feet or greater (currently 4,000 square feet), which would make approximately 7,300 additional parcels eligible to provide this additional housing option.
- Increasing the maximum gross floor area of a backyard cottage to 1,000 square feet (currently 800 square feet), which would provide more livable area and increase the likelihood of two-bedroom backyard cottages to better serve families with children.
- If a backyard cottage is built above a garage, the garage square footage will no longer count toward the maximum floor area, as it might result in an unreasonably small living space.
"With these amendments to the existing code, we could see thousands of new housing units that simultaneously fit into the context of a neighborhood and serve property owners," said Councilmember O'Brien. "By expanding the availability of backyard cottages and mother-in-laws, someone might be able move to a neighborhood they otherwise couldn't afford while helping a homeowner who needs an extra source of income to afford to stay where they are. It's a win-win."
The legislation was developed utilizing feedback from neighborhood community meetings, from architects, and from current backyard cottage owners. A summary of the public feedback is available here. The former Seattle Department of Planning & Development also conducted an analysis of current backyard cottages in Seattle and a review of peer cities' backyard cottage model.
Backyard cottages, also called detached accessory dwelling units (DADUs), are separate living spaces on the same property as an existing single-family house. Mother-in-law units, also referred to as accessory dwelling units (ADUs), are separate living units generally located within a single-family house.
Personal Stories from Backyard Cottage Owners
"My backyard cottage is for my Mom, who at 80 years old needs to be close but is not ready for assisted living."
"Our original intent was a glorified garage with electrical and plumbing, as a short-term place for friends to stay,. The permitting process forced us to expand the project into a more traditional living space. Now that it is a full blown space (kitchen with range, washer / dryer, loft, etc.) we love the rental income (from a long-term tenant)."
"My neighbors really like the cottage and often stop by to say so, or ask how they might build one.. One reason it worked well for me is that I already have a very small house (650 sq ft) and adding the cottage doesn't overwhelm the space."
"I was looking for two houses on one lot when I bought this house. I needed the second income as a single woman."
Summary of Proposed Changes
|#||Policy Area||How It Is Today||Proposed Change|
|1||Attached Accessory Dwelling Unit (ADU) and Detached ADU (DADU) on the same lot||A lot with or proposed for a single-family dwelling may have no more than one accessory dwelling unit.||Allow a property to have both an ADU and DADU within the existing building envelope
|2||Off-street parking requirement||One off-street parking space is required for the accessory dwelling unit, unless located in an urban center or urban village.||Remove requirement for off-street parking
|3||Owner-occupancy requirement||An owner must occupy either the principal dwelling unit or the accessory dwelling unit.||Require owner-occupancy for 1 year, then requirement expires
|4||Minimum lot size for DADUs||The current minimum lot size for a site with a DADU is 4,000 square feet.||Reduce the minimum lot size for a site with a DADU to 3,200 sq. ft.
|5||Maximum square footage of a DADU||The maximum gross floor area of a DADU is 800 square feet including any garage and storage areas. The maximum gross floor area of an ADU is 1,000 square feet.||Increase the maximum gross floor area of a DADU to 1,000 square feet; exclude garage and storage areas
|6||Rear yard coverage limit||A maximum of 40% of a rear yard may be covered by accessory structures and any portion of the main house. This limit is in addition to the overall lot coverage limit for a single-family lot||Increase rear yard coverage to 60% for one-story DADUs
|7||Location of entries||DADU entrances cannot face the nearest side or rear lot line unless that lot line abuts an alley or other public right-of-way.||Allow DADU entrances on any façade, provided it is 10 feet from the lot line if located on the façades facing nearest side or rear lot line (unless abutting right-of-way)
|8||Height limit||The maximum height limit depends on the width of the lot; on wider lots, a taller DADU is permitted (see Table A below)||Increase maximum height by 1-2 feet and simplify code (See Table B below)
|9||Roof features||Exceptions for roof features for a accessory units are not permitted.||Allow exceptions from height limit for projections (e.g., dormers) that add interior space.
Height Limits for DADUs
Table A - Current
|Lot width (ft)||<30||30-35||35-40||40-50||>50|
|Base height (ft)||12||14||15||16||16|
|Additional height for pitched roof (ft)||3||7||7||6||7|
|Additional height for shed/butterfly roof (ft)||3||4||4||4||4|
Table B - Proposed
|Lot width (ft)||<30||30-50||>50|
|Base height (ft)||14||16||18|
|Additional height for pitched roof (ft)||3||7||7|
|Additional height for shed/butterfly roof (ft)||3||4||4|
- Update on Backyard Cottage Legislation & Next Steps
- More information from the Office of Planning and Community Development
- Read the proposed legislation
- Removing Barriers to Backyard Cottages - DPD Report and Analysis (October 2015)
- Seattle DPD Presentation
- City of Portland Presentation
- State of Oregon Presentation
- CAST Architecture Presentation