WA Senate passes bill allowing duplexes, fourplexes in single-family zones

The Washington state Senate passed legislation Tuesday that would allow duplexes or fourplexes in most neighborhoods in most cities throughout the state, regardless of local zoning rules that have long limited huge swaths of cities to only single-family homes.

House Bill 1110, which passed on a bipartisan 35-14 vote, aims to increase housing supply and density by allowing more homes on plots of land that have traditionally allowed only one. Increasing housing supply, supporters say, is critical to combating a housing crisis that’s brought escalating home prices and homelessness numbers throughout the state.

“We simply don’t have enough housing in this state,” said Sen. Yasmin Trudeau, D-Tacoma. “This problem affects every city in every county across the state and it’s a bigger problem than any city or county has been able to tackle so far.”

Opponents argue that planning and land use decisions should be handled locally and that the bill would be a gift to developers while doing little to increase the supply of affordable housing.

“I support the local communities being able to determine what their community looks like without the state of Washington coming down with a hammer telling them they must do this,” said Sen. Phil Fortunato, R-Auburn.

The bill must now return to the House, where it passed in a different form last month. Among other changes, the Senate version is more lenient in the requirements it places on small cities in Seattle’s suburbs. The House could either approve changes made by the Senate or the two bodies could attempt to work out their differences.

The bill’s House co-sponsors, Rep. Jessica Bateman, D-Olympia, and Rep. Andrew Barkis, R-Olympia, stood in the wings of the Senate chamber to watch the vote.

The proposal is the flagship piece of a broader legislative push to increase the production of “middle housing” in Washington, dwellings like duplexes, town homes and backyard cottages that provide more housing units than single-family homes but are smaller than traditional apartment buildings.

“Hard to overstate what a sea change this is for the state of Washington taking proactive action on zoning reform to create more housing choices,” wrote Dan Bertolet, director of housing and urbanism for the Sightline Institute, which support upzones.

It would not ban the construction of single family homes, but it would stop cities from requiring neighborhoods to be made up of exclusively single-family homes.

Sen. John Braun, the Republican minority leader, touted the bill as a protector of private property rights.

“When the cities say you can only build one house on your half-acre lot,” Braun, R-Centralia, said, “that restricts your right to use your property as you would like.”

The state Department of Commerce estimates Washington needs to build an additional 1 million homes over the next two-plus decades to keep pace with population growth. 

The Senate passed a slightly scaled back version of the bill.

Cities with more than 75,000 people must allow fourplexes throughout the city. They must allow sixplexes if they’re within a quarter-mile of a major transit stop or if two of the six units are affordable housing.

Cities with between 25,000 and 75,000 people must allow duplexes almost everywhere. They must allow fourplexes if they’re within a quarter-mile of a major transit stop or if one of the four units is affordable.

Seattle’s smallest suburbs — cities with fewer than 25,000 people like Woodinville, Kenmore and Tukwila — would have to allow duplexes. In the House version of the bill, these cities would have been required to allow fourplexes and sixplexes.

The requirements would not apply to environmentally critical areas or threatened watersheds around drinking water reservoirs.

Similar legislation has failed in recent years, as cities have lobbied to maintain their traditional, local grip on zoning regulations. But supporters this year worked extensively on the legislation with the Association of Washington Cities, which started the legislative session neutral on the bill, before giving its muted support last week.

“Cities around the state are reaching to the middle to work on and eventually support many creative policy changes such as this middle housing bill — because our housing challenge requires an all-hands-on-deck approach,” Carl Schroeder, the group’s deputy director of government relations, said last week.

“What I saw from the cities was a willingness to get to yes,” said Sen. Mark Mullet, D-Issaquah.

States have increasingly stepped in to override municipal rules as populations grow and housing stocks fail to keep pace. Oregon eliminated single-family zoning in 2019 and California largely did the same in 2021.

In its first year of existence, California’s law, which allows property owners to build up to four homes on a single-family parcel, was used sparingly, a study from the University of California, Berkeley, found.

Staff reporter Claire Withycombe contributed to this report.

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