At least 36 cities in Oregon and Washington updated rules in 2017 and 2018 to make it easier for homeowners to build backyard cottages, basement apartments, and mother-in-law suites.
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Editor’s note, 1/11/19: We updated this article to add information about 2018 code changes in Anchorage, Alaska.

Cascadians are hungry for housing choices. One way they showed it in 2018 was by loosening restrictions on accessory dwelling units (ADUs) in cities across the region—from Bellingham to Yakima, Florence to Portland. In all, at least 37 Cascadian cities—across Alaska, Oregon, and Washington—updated rules in 2017 and 2018 to make it easier for homeowners to build backyard cottages, basement apartments, and mother-in-law suites. Twelve more Oregon cities have plans in the works to liberalize rules in 2019.

Most of these policy wins happened in Oregon, where 2017 ADU legislation required cities with populations of 2,500 or more to permit at least one ADU per single-family house. So far, the law has prompted at least 26 cities to remove legal barriers to these green, affordable homes. In fact, several cities pushed beyond what the law required by reducing off-street parking requirements and fees and even permitting two ADUs per lot.

Meanwhile, at least ten jurisdictions in Washington relaxed ADU rules in various ways in 2017 and 2018, including legalizing backyard cottages, reducing fees, and rolling back parking mandates. Seattle, however, spent the year battling legal appeals filed by anti-housing activists to stop proposed ADU liberalization.

In Alaska, Anchorage made big strides toward legalizing ADUs and making them easier, and less costly, to build.

The diversity of cities extending a welcome to ADUs this year—from urban centers to small towns—demonstrates a growing recognition that these modest homes work for people from many walks and stages of life: seniors who want to age in place, new families in need of rentals suitable for young kids, or homeowners who hope to provide a place to live for their adult children, disabled siblings, or aging parents.

Here’s our rundown of the region’s five biggest ADU policy wins of 2018.

Cascadia’s Five Biggest ADU Wins in 2018

5. Removing owner occupancy requirements

Requiring homeowners with ADUs to live onsite discriminates against renters, plain and simple. It also takes away owners’ future flexibility to move if circumstances change, which can dissuade them from taking the financial risk to build an ADU. And it outright eliminates ADUs from the nearly 20 percent of detached houses that are rentals across Oregon and Washington.


City councilors in Tigard, a suburb of Portland, removed the city’s owner occupancy requirement in 2018. Planners in Madras, a rural town with 6,800 residents, say the city may follow suit as it considers allowing ADUs in 2019. Salem preceded these cities when it legalized ADUs in 2017 without requiring owners to live on site. 


Two jurisdictions struck the owner occupancy barrier from their law books: Clark County and Olympia. Vancouver led the way, eliminating its requirement in 2017.

4. Slashing fees

Permitting, impact, and utility connection fees can heap tens of thousands of dollars on ADU development costs, a sticker shock that can deter homeowners from taking on an ADU construction project. Often the fees are equivalent to those placed on typical detached, “single-family” homes, and therefore disproportionate to the reduced impact of a smaller home. Portland’s surge of ADU permit applications following its 2010 decision to temporarily suspend system development charges (SDCs)—fees that previously could run as high as $16,000 per ADU in the city—suggests that cutting fees may be one of the most impactful policy changes for stimulating construction.


Portland’s city council voted in 2018 to indefinitely suspend SDCs for ADUs built by homeowners who commit to renting their new living space as a long-term rental. Three other cities—Florence, Hubbard, and Mt. Angel—also waived or reduced utility connection and impact fees on ADUs, allowing homeowners to save as much as $13,000 on ADU construction. Though Florence’s waiver is temporary, the city may eventually make the exemption permanent, just like Portland did.

Salem and Springfield preceded these cities by reducing their ADU SDCs in 2017. Salem charges ADUs based on multi-family, rather than single-family, rates, and exempts the small homes entirely from water and sewer charges. Springfield temporarily waived several SDCs in 2017, resulting in savings of about $5,000 in construction cost per ADU. 


Three jurisdictions—Bellingham, Clark County, and Renton—cut various ADU fees. Bellingham’s city council reduced park impact fees by about $1,000, and exempted ADUs that don’t add building square footage from all impact fees, saving homeowners as much as $3,000 on an ADU built inside an existing house.

Clark County lowered ADU transportation, park, and school impact fees to 25 percent of the county’s charges on multi-family residences, which are already less than the fees on detached, full-sized  homes.

Renton’s city councilors extended through 2020 their 2017 decision to halve permit and impact fees on all new ADUs, which together can cut as much as $11,000 from an ADU construction budget. Like Portland, Renton saw a surge in ADU permit applications: in the year following the fee reduction Renton’s ADU stock grew by 50 percent. If future renters in the city are lucky, this success story will convince Renton to follow in Portland’s footsteps and make the fee suspension permanent.

3. Reducing off-street parking requirements

Off-street parking requirements make ADU construction more expensive, perhaps by as much as $10,000 per space. They also preclude ADUs on lots can’t that fit an extra parking space because they’re too small or do not have easy access to a street or alley. At least three Cascadian cities chose to reduce or eliminate off-street parking requirements in 2018.

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  • Alaska:
    Anchorage inserted a first-of-its-kind provision into its 2018 revamped ADU code, permitting property owners to forgo the city’s requirement of one off-street parking space per ADU if they sign no-car covenants. ADU owners who choose to take advantage of the covenant would commit to not allow any person who owns or leases a car to occupy their ADU. In selected other cases, city traffic engineers have the power to allow homeowners to use on-street parking to meet the city’s ADU parking requirement.

    Tigard exempted ADUs within 2,500 feet of transit service from providing off-street parking. And in its new ADU ordinance, Florence eliminated off-street parking for ADUs in neighborhoods that the city determines have enough on-street parking capacity to accommodate the additional residences. In its 2017 ADU code, Salem did not include any off-street parking requirement. 


    Bellingham reduced its parking requirement from one space per bedroom to one per ADU. Olympia removed its off-street parking requirement for ADUs on lots where 2 off-street spaces are already available.

    2. Welcoming backyard cottages

    Cities often permit attached accessory dwellings before they permit detached backyard cottages, because allowing an extra building on the lot tends to incite more controversy among neighbors. But because not all houses can accommodate an attached or internal ADU, this allowance gives owners a second option for adding another dwelling to their lot. Typically tucked away behind the main house, backyard cottages hardly change the appearance of a neighborhood and provide additional privacy to tenants.

    In 2018, Anchorage permitted backyard cottages in all residential zones except single-family zones. That’s a big win for smart growth in Anchorage. Extending the same flexibility to homeowners in single-family zones would amplify the benefits and provide more housing options in neighborhoods across the city.


    Florence, Gresham, Hubbard, Mt. Angel, Tigard, and Tualatin permitted backyard cottages in their detached home zones in 2018. Madras will likely follow their lead in 2019, having already proposed the same, according to the city’s planners. Salem preceded these cities, legalizing cottages in 2017.


    Bellingham, Tukwila, and Yakima all granted new allowances for backyard cottages in their single-family zones in 2018, right on the heels of Everett, which opened its backyards to these small homes in 2017. Since legalizing these small, detached homes, Bellingham has already seen nearly 30 permit applications from homeowners interested in building a cottage in their backyard.

    1. Permitting two ADUs per lot in zones restricted for detached houses

    Allowing two ADUs per lot instead of one doubles the potential benefits of ADUs. More ADU housing options means greater progress toward creating walkable neighborhoods, growing the region’s energy-efficient housing stock and supporting car-lite living. More ADUs per lot also multiplies their affordability benefits and their neutralizing effect on single-family zoning’s invisible walls of economic exclusion.

    In 2018, in Oregon, Tigard and Troutdale legalized two ADUs per single-family lot—an attached unit plus a backyard cottage. Madras may follow suit in January 2019 when the city council considers a proposal to allow two ADUs on large lots, those exceeding 7,500 square feet. The city may even go a step beyond by permitting up to four homes per lot. The city already permits duplexes on the majority of its single-family land and planners expect the city will allow each duplex unit to have its own backyard cottage.

    While Portland still does not permit two ADUs per detached house, Seattle is on track to finally make this code change in 2019. Meanwhile, Vancouver, British Columbia, has long permitted two ADUs per lot and has reaped the rewards of additional rental options in neighborhoods across the city.

    Next Steps for ADUs in Cascadia

    In 2018, numerous Cascadian cities have showed they are ready to start cutting the reams of restrictive regulations that have hamstrung ADU construction for decades. In 2019, this momentum may get a major boost at the state level: legislators in Oregon and Washington plan to introduce bills that would require local jurisdictions to reduce barriers to ADU construction.

    Oregon’s legislation would build on the ADU legalization the state passed in 2017. Washington’s would be the first state-level update to ADU rules since the 1993 passage of the state’s Housing Policy Act, which requires cities with populations above 20,000 to permit ADUs in single-family zones.

    Leadership on ADU policy at the state level has huge potential to help the region respond to the growing need for flexible housing choices for all our neighbors. The year 2018 was a big one for ADUs in Cascadia, but 2019 could be even bigger.

    Note: Oregon’s SB 1051, which successfully passed during the state’s 2017 legislative session, requires cities with populations of 2,500 or more to allow at least one ADU per single-family home in areas reserved for detached houses, affecting 103 cities in total. Sightline reviewed ADU regulations in 55 of these cities with a range of populations. We found 26 that changed or implemented new ADU regulations since the legislation passed; these are the cities we included in our count in this article. In addition, we found 19 cities that have not passed an ADU ordinance yet in response to SB 1051 but may do so in the future, and 10 that will not update their regulations because their codes are already in compliance with SB 1051. Sightline has not yet reviewed ADU regulations in the other 48 cities in Oregon that fell under the purview of SB 1051.