It took a minute, but America is finally warming up to a revolutionary construction paradigm that could shorten commutes, lower housing costs, and ease the way to racial and socioeconomic integration in cities and suburbs: the apartment.

A week after Minneapolis moved to become the first U.S. city to end single-family zoning, Rachel Monahan of Willamette Week reports that the speaker of the House of the Oregon Legislature, Rep. Tina Kotek, is drafting a bill that would require Oregon cities to allow apartments in all residential neighborhoods.

Kotek’s proposal would compel cities to permit duplexes triplexes, fourplexes, and cottage clusters as-of-right in all urban areas zoned for detached single-family housing (with an allowance for reasonable design and siting regulations). Jurisdictions with over 10,000 residents would have 16 months to revise their zoning codes accordingly, or else be governed by a state code enabling the construction of “missing middle” housing.

“The state’s housing crisis requires a combination of bolder strategies,” Kotek, who represents Portland, said in a statement provided to Slate. “Oregon needs to build more units, and we must do so in a way that increases housing opportunity for more people. Allowing more diverse housing types in single family neighborhoods will increase housing choice and affordability, and that’s a fight that I’m willing to take on.”

When it convenes in January, the Oregon statehouse will become the latest forum for an escalating national debate on the wisdom of single-family zoning. Driven by high rents, long commutes, and a growing awareness of the racist history of American city planning, lawmakers are questioning the codes that have long kept apartments out of wealthy, white neighborhoods.

In California, the state legislature permitted accessory dwelling units statewide last year, spurring a granny-flat boom in the state’s expensive coastal areas. This session, State Sen. Scott Wiener has proposed SB 50, a revised version of his bill to force the state’s municipalities to permit denser housing near transit—effectively legalizing apartment buildings in all of San Francisco and much of Los Angeles.

Seattle will vote to allow larger buildings in two-dozen neighborhoods in March.

And in Portland, activists and homeowners have sparred over a plan to build more, as the city government has dawdled and delayed.

Could the state beat them to it? Homelessness in metro Portland, where almost half of Oregon’s population lives, was a major issue in the 2018 gubernatorial race. Housing affordability is also a problem in the state’s smaller cities and rural areas. Democrats have a big majority in both houses of the legislature, though the sanctity of the single-family home neighborhood has traditionally cut across party lines.

One encouraging precedent is SB 1051, a 2017 law that legalized accessory dwelling units statewide, including in single-family home neighborhoods. That law initially was written to permit duplexes statewide, but was pared down to gain support. Ultimately, it passed unanimously in the Oregon House, drawing support from deregulation-friendly Republicans.

Infill building types such as townhouses, duplexes, and small apartment buildings—known as the “missing middle”—are increasingly seen as the most equitable and sustainable way to promote population growth in U.S. cities. In places where infill housing is all but forbidden, like Los Angeles, homelessness has skyrocketed, traffic has worsened, and development has been pushed to natural land on the urban fringe. Transportation is now the nation’s largest source of greenhouse gas emissions.

In Portland, as in many cities, neighborhoods that forbid attached housing tend to be considerably wealthier than the city at large. Their restrictions are also holding down the city’s collective housing stock growth. In a November analysis, consultants concluded that Portland’s plan to allow bigger buildings would over 20 years approximately triple the number of new units, to 38,000, and lower the average rent of a new unit by 56 percent. Approximately 45 Oregon cities would have their local zoning preempted by Kotek’s proposal.