Tara Siegel and her partner love living in Arlington, Va., just outside Washington, D.C., but they'd really like more space than the two-bedroom apartment they rent. Recently they started browsing on Zillow for a place to buy.

"We saw a lot of homes," Siegel says, "but when we brought it back down to what we could afford, what our price range was, suddenly all the homes disappeared."

It was a rude surprise. The couple makes above the local median household income, which is more than $120,000. They knew houses can approach a million dollars, but it turned out that even tw0- or three-bedroom condos are too pricey.

"It was sad for me and made me feel, just, discouraged ... for our community," says Siegel, who is 35 and a State Department contractor.

Arlington is among a growing number of places debating an end to the single-family zoning mandates that have defined the iconic American suburb. The hope is to create housing that more people like Siegel can afford, but the changes are controversial.

Three states — Oregon, California and Maine — and a handful of cities have already opened up their zoning. Housing experts say this is key to eventually ending the severe housing shortage — a deficit of millions of homes — that has been a main driver of sky-high prices. These new laws legalize all kinds of housing that were banned for generations, including duplexes, townhomes and smaller apartment buildings. It's called the "missing middle" and is meant to fill the gap between single-family homes and high-rise apartments.

Supporters are motivated by more than affordability. Racial equity is a goal, since many single-family zoning laws were used to segregate cities by race and class. And denser housing can help limit the reliance on cars and long commutes that exacerbate climate change.

The zoning changes also address a serious demographic mismatch. Most residential land in many cities is devoted to stand-along homes that have grown ever bigger, even as the average size of households has shrunk: Today, nearly two-thirds are just 1 or 2 people.

Relaxing single-family zoning is controversial, and many homeowners oppose it

Despite a growing push for denser housing, these decisions can be tough to pass. In fact, after backlash in Gainesville, Fla., city commissioners recently moved to reverse last year's decision to end single-family zoning.

On a Saturday in January, Arlington's County Board strapped in for five hours of public comment from more than 150 people. Community sentiment on the missing middle plan was sharply divided.

"Our street can't handle that," said opponent Michael Lynch. "The neighborhood can't handle that. The school system can't handle that. And the city infrastructure can't handle that."

Many current homeowners fear added density will lead to parking nightmares, fewer trees, overtaxed county services, and more impervious surfaces that could cause flooding. They also worry it will change the character of their neighborhoods, and they prefer that apartment buildings stay in dense commercial corridors.

"We don't have the space to incorporate a city, or urbanized living, within this small village of a community that we have," says Julie Lee, president of a neighborhood civic association and founding member of Arlingtonians for Upzoning Transparency, a group fighting the plan.

Lee says "missing middle" housing would still be too costly for many. And she worries the plan could further incentivize the tearing down of smaller, more affordable single-family homes in favor of multifamily units that could be about as expensive.

Supporters like County Board member Katie Cristol say it's important to change zoning rules that have long priced out families of color. And she worries about the growing gap between multimillion dollar single-family homes and subsidized affordable housing — and the people who are falling through it.

"We risk losing the future of our ... young to mid-career professionals who want to make Arlington home permanently," Cristol says. That's a sizable number of people, she adds — Arlington is majority-renter and its largest age demographic is 25 to 34.

After two days of contentious public comment, Arlington's board scaled back key aspects of the plan that is now up for final consideration, in an attempt to placate opponents. It lowered the maximum number of units the board could ultimately approve from eight to six. And it added an option that would say five- to six-unit buildings could be constructed only near transit or on sites bigger than 12,000 square feet. That would mean many areas of the county would be opened just to two- to four-unit homes.

The move brought condemnation from the Arlington NAACP, whose president tweeted, "This is de facto segregation and our leaders missed the mark on such a historic vote."

A final vote, which will solidify details of the policy, is planned for March.

New zoning laws have not produced much new housing so far

"Missing middle" zoning changes are specifically designed so that neighborhoods aren't completely transformed overnight. They may limit how much construction can happen each year, and it'll likely take decades for big change. Home construction generally also slowed over the past year or so.

Still, the small amount of housing built so far in places where zoning laws have passed provides a reality check.

"It is not yet clear if this wave of state and local zoning changes will result in a significant number of new homes," concludes a recent analysis by the Terner Center for Housing Innovation at the University of California, Berkeley.

The researchers held roundtable conversations with developers in seven states to understand what's holding up construction.

"I was surprised that there was not more enthusiasm around building these smaller scale housing types amongst the developers that we interviewed," says co-author David Garcia. "There is a belief that zoning is the key to unlocking all of these new housing units, and I think maybe it's more like the first step."

The report identifies a number of barriers. One example: Garcia says it simply won't work if a developer must fit, say, a four-unit building in the exact same space they'd have put a 2,000-square-foot house. He says cities need other design and land-use changes to allow more square feet, and perhaps a smaller setback from the street. Ending parking requirements can free up space that would have been used for a driveway.

Another barrier is the high cost of construction and land, a major challenge in places like California. Garcia says it makes the economics of two- to four-unit buildings challenging; developers say they find six to eight units or higher more financially viable.

He cites Portland, Ore., as a model for making changes beyond zoning that have helped the city permit dozens of fourplexes. He's hopeful other cities can use these lessons to craft the most effective policies.

One advantage for developers: "Missing middle" zoning laws generally let them avoid the neighborhood opposition and appeals process that hold up so many housing projects.

"The appeal provides unpredictability and risk for a builder. And when you're talking about small builders, they can't take that risk," says Eli Spevak, who owns a company called Orange Splot in Portland.

He's developing two townhomes and a couple of six-unit buildings, which will not be subject to appeal. "If you check all the boxes — and it's a long list — then you're guaranteed to go to a building permit."

Newly built 'missing middle' homes will still be out of reach for many

For the most part, "missing middle" housing is not intended for the lowest-income Americans, though laws can include incentives for that. Spevak is only allowed to build six units because three of them will be publicly subsidized.

The bulk of these duplexes and other multifamily homes are market rate, and that's not exactly affordable for a lot of people right now. Still, they can cost less than single-family homes in the same neighborhood. Spevak says his non-subsidized units will sell in the $400,000 range, while nearby homes go for $700,000 to $800,000.

In Arlington, the county's own estimates find that newly developed duplexes would run above $1.1 million, which is actually more than some of its older, smaller single-family homes. Supporters of the zoning change say those units would become relatively more affordable as they age over time.

F0r now, that's not much help to Tara Siegel, the renter who wants a bigger place. She and her partner have since put their Arlington home search on pause, and are questioning if they even want to buy a home at all. But she still supports the zoning proposal.

"Maybe I won't be in Arlington because of it," Siegel says, "but 'missing middle' could help some people down the line."