Commission legalizes ADUs in unincorporated Thurston County
Thurston County Board of Commissioners voted unanimously on Tuesday to legalize Accessory Dwelling Units (ADUs) in unincorporated areas of Thurston County, a change the commission has been eyeing since 2018.
Alternately known as “backyard cottages” or “mother-in-law-units,” ADUs are small, separate living units built on the same lot as a single-family home.
Although ADUs are already legal within the urban growth areas of Olympia, Lacey, Tumwater, and Grand Mound, the county controls zoning codes in unincorporated areas.
The county had already allowed something called a Family Member Unit in unincorporated areas, defined as a “temporary mobile/manufactured or modular home” that can only be occupied by a family member of the homeowner, and must be removed when that family member leaves.
Those rules have been difficult to enforce in practice, according to a staff report on the county’s website.
The new rule specifies that ADUs shall “visually match in type, size, trim, and materials” the primary house, and can be no larger than 40% of its square footage or 1,500 square feet, whichever is less. The exception is that the ADU can be 50% of the square footage if the ADU is attached to the home.
For a conversion, such as when a homeowner who wants to convert a garage into an ADU, the “footprint” cannot be expanded, which would imply that you could put a second floor on it but not expand its dimensions.
The ordinance limits ADUs to one per lot, and they cannot be built on lots that already have an Family Member Unit.
Not every lot will be eligible to build a cottage-style ADU, because density controls in the county’s zoning code still limit the number of residences on a given acreage of land. For example, in one the county’s most ubiquitous zoning districts, RRR 1-5 (Rural Residential Resource 1 unit per 5 acres), a lot must be at least ten acres large to build a detached ADU, because it counts as a second residence. (Attached ADUs or garage conversions are not bound by the same density controls).
There are no off-street parking requirements for ADUs, unless an existing parking space is removed by a garage conversion. That decision, which the county Planning Commission debated at a public hearing in August, puts the county in line with the city of Olympia, which recently voted to remove the off-street parking requirement for ADUs are part of the Housing Options Code Amendments.
The Board of County Commissioners held a public hearing on the change on Nov. 10, and about a dozen people testified in support of the change. One person was upset that the presumably city-dwelling commissioners would make rules affecting residents of unincorporated areas, but did not address the ordinance specifically.
Roland Kouhsen, who lives in an unincorporated area near Hawks Prairie and wants to convert his garage into a room for his father, supports the policy and said he found the current rules about Family Member Units to be strange.
“It struck me as kind of odd and a little bit crazy that it would be okay for us to buy an RV, park it on our property, and have my dad live in there, but not inside of an existing detached garage,” Kouhsen said at the hearing.
Other commenters welcomed the additional options for families to live together, with one person saying she’d like to have a close friend live in an ADU on her property to help her as she ages, which was not allowed before.
Written comments received by county staff were overwhelmingly supportive of the change as well, according to Associate Planner Andrew Boughan.
Boughan said the county received 104 public comments about the plan: 75% were in support of making ADUs legal; 21% asked questions, expressed concerns, or provided feedback; and 4% were against it.
The change puts Thurston County in line with many other counties across Washington that allow ADUs, including King, Pierce, Snohomish, Clark, and Whatcom.
This story was originally published December 16, 2020 at 5:45 AM.
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