By Erica C. Barnett

Maybe calling them “stacked flats,” rather than “apartments,” was a stroke of genius.

On Tuesday, the City Council adopted legislation that will allow eight-unit apartment buildings on every residential lot in the city—or up to ten units if the developer preserves trees or adds “green“ landscaping features, like bioswales and green roofs, to new housing construction. These apartments are known as “stacked flats” because they’re on top of each other, unlike multi-level townhouses that are generally offered for sale, not for rent, at prices far out of reach to most Seattle residents.

The legislation, part of the comprehensive plan package the city council adopted this week, doesn’t spell out eight units, but if you do the math, that’s what it works out to on a 5,000-square-foot lot with a standard 60 percent lot coverage.

Developers who go for the green bonuses will also get to build up to four stories, rather than the standard three. (Logically, four stories makes more sense for eight-unit buildings, allowing two per floor, but maybe some enterprising new councilmember will suggest revisiting that limit). That’s more density than the state required cities to allow under 2023’s HB 1110, which allows four units on all residential lots statewide, or six if two of the units are affordable. The council adopted interim rules to comply with HB 1110 earlier this year.

The changes were part of the council’s final vote of 2025 on the city’s comprehensive plan, the long-debated, much-delayed document that governs how and where Seattle can grow. The council’s comprehensive plan committee already adopted most of the changes that were finalized this week back in September, but had to put off a final vote while the city’s planning department completed environmental review on some new amendments and gave the public an opportunity to comment on the changes

Mayor Bruce Harrell’s comprehensive plan proposal came in a year behind schedule, a delay that has pushed some comprehensive plan legislation to next year, including legislation to enact new zoning in low-rise areas, establish new boundaries for dense “regional centers” and urban centers, and potentially add more “neighborhood centers” near transit stops where taller apartment buildings will be allowed.

Density opponents on the council will have another opportunity to argue that Seattle isn’t ready for more housing, and that the city hasn’t done sufficient outreach to “neighborhoods,” meaning single-family homeowners, before allowing renters to live in new parts of the city. But, thanks mostly to Harrell’s delays, they’ll be joined by two new council members who are fans of density, Eddie Lin and Dionne Foster, and a mayor who’s an unabashed urbanist.