It wasn’t long ago that now-vibrant downtown Los Angeles felt quiet on evenings and weekends. Once the bankers and lawyers and office managers went home, you could walk for blocks without finding somewhere to have a cup of coffee. Dinner options were scant, and safety on the dark, empty streets at night was a concern. But over the past decade or two, things have changed: Developers have transformed Beaux-Arts banks, Art Deco office buildings, and early 20th-century theaters and warehouses into loft apartments, restaurants, galleries, and clothing shops. Grocery stores and dog parks soon followed. Now, the streets of downtown L.A. bustle long after 5 p.m.

Similar changes are happening all across the country. According to the 2010 census, more than 80 percent of Americans now live in urban areas—and that number is only growing. Where most people once aspired to live in suburban houses with a yard and a garage, a new generation is embracing the diversity, historic character, and less car-centric lifestyle that a city provides. Baby boomers, drawn to those same qualities, are following. Yes, cities are having a big moment—and that’s creating a huge opportunity for the preservation community.

The National Trust has been working for decades on initiatives designed not only to keep the historic fabric of cities intact, but also to improve the lives of urban residents. Its Main Street America program, relaunched as an independent subsidiary in 2013, has helped revitalize thousands of downtowns and commercial corridors over the past 36 years, and since 2000 the National Trust Community Investment Corporation (NTCIC) has placed the National Trust at the table with developers and business owners to identify financing that helps old buildings serve their communities again. More recently, the National Trust established the Preservation Green Lab to promote more sustainable cities, neighborhoods, and communities through the reuse and retrofitting of old buildings.

Increasingly in urban communities, preservation is less about saving individual buildings than it is about making entire city blocks and neighborhoods more dynamic. It’s become a tool for shaping better, more equitable cities—places that support diverse populations, that are unique, that have character. By turning old buildings into new places to live, preservation encourages healthier, more sustainable lifestyles, where people can walk or bike to stores, restaurants, and work. Using existing structures to house new businesses helps create jobs and spurs economic growth. But for every successful adaptive reuse, there is a developer proposing the demolition of historic buildings to make way for new construction.

“We want preservation to become the default for cities,” says National Trust president Stephanie K. Meeks. “We want cities to understand that historic buildings are a resource, and to have their first response always be to figure out how to restore and reuse them and keep them in active service for their community.”

Research by the Green Lab demonstrates the important role preservation can play in taking on challenges such as climate change, rising housing costs, and gentrification. The results of its 2011 study, The Greenest Building: Quantifying the Environmental Value of Building Reuse, strongly support the idea that the greenest buildings are those that are already built. To encourage the rehabilitation—rather than demolition—of old buildings, the National Trust and the Urban Land Institute joined forces in 2012 to create the Partnership for Building Reuse.

And just two years later, the Green Lab published Older, Smaller, Better, a study aimed at measuring how the character of historic buildings and blocks influences neighborhood vitality. Using geographic information system (GIS) technology to measure the age and size of buildings against how they perform on social, cultural, and economic levels generated clear results: Neighborhoods with a mix of older, smaller buildings have greater economic and social vitality than areas with mostly newer, larger buildings. Using that same GIS technology, the Green Lab is currently working to create an atlas of existing buildings and blocks across the country, which will be released in November.

Harvest Commons

By the time Harvest Commons on Chicago’s Near West Side opened in 2013, it had been decades since the six-story Art Deco building offered a safe place to sleep. Opened in the 1930s as the residential Union Park Hotel, it fell into decline after new owners took over in the 1960s, renaming it the Viceroy Hotel. The building was an epicenter for criminal activity when the city took control and closed it in 2006. Five years later, Heartland Housing (a branch of the antipoverty nonprofit Heartland Alliance) and nearby First Baptist Congregational Church won the contract to redevelop the dilapidated structure.

The partners had a clear vision for an affordable housing complex.

“We wanted to save the building for its historic merit and turn a liability into a community asset, but we also wanted to ameliorate the effects of a rapidly gentrifying neighborhood on folks experiencing homelessness,” says Nadia Underhill, Heartland Housing’s director of real estate development.

Working with Landon Bone Baker Architects, the team repaired and restored the hotel’s brick-and-terra-cotta facade. Inside, they restored the lobby, stairwell, and arched ceilings, while retaining original window openings and adding sustainable features such as geothermal heating and cooling and a solar hot-water system. They created 89 single-occupancy units, meeting spaces, a computer lab, offices for on-site supportive services, an urban farm, and a teaching kitchen for classes on nutrition and food preparation.

The $19.8 million project was funded through a combination of public and private sources, and the developers took advantage of tax credits for low-income housing and historic preservation.

“It’s an anchor now,” Underhill says. “It’s changed people’s perceptions of the neighborhood, and it’s providing the stability we hoped it would.”

Fox Theater

When now-California Gov. Jerry Brown was mayor of Oakland from 1999 to 2007, he developed an ambitious plan for Oakland’s downtown that centered around attracting new residents.

“The aim was to create what we call a ‘24-hour downtown,’” says Patrick Lane, development manager for the city of Oakland. “By that we mean people living there, with things happening late at night and early in the morning. An active downtown.”

Part of the plan, Lane says, was bringing back entertainment and nightlife venues such as the Period Revival–style Fox Theater in the city’s Uptown District. When it opened in 1928, the grand movie palace helped support a thriving shopping and entertainment district. But the last movie played there in 1965. The building closed completely in 1985, sitting vacant until the city purchased it 11 years later.

Heart of Louisville

Many of Louisville, Kentucky’s historic buildings and neighborhoods remain intact. That’s part of what makes the city unique.

“But it’s not unique in nearly every other way,” says Margaret O’Neal, senior manager of the National Trust’s Preservation Green Lab. Like many cities of its size, she says, Louisville saw a sharp population decline in the wake of 1960s urban renewal and highway construction projects. Recently, its downtown has experienced a surge of new life—the same thing that’s happening in cities across the country.