Remember when we were going to save the suburbs? In 2008, Ellen Dunham-Jones, AIA, and June Williamson released Retrofitting Suburbia, a handbook for turning sprawl into walkable, sustainable, more urban places. The book got national media attention, Dunham-Jones gave a TED talk, and for a while, dead malls were the topic du jour.

Then the recession came, putting the brakes on many suburban redevelopment plans and shifting the attention of designers and policymakers elsewhere. We started to see the effects of climate change, such as powerful, more frequent storms, and grew concerned about resilience and adaptation, not just prevention. Meanwhile, Generation Y’s preference for city living intensified, and among designers, conversation shifted to designing for health and social impact, with a renewed interest in serving inner-city communities and the developing world.

The elephant in the room: In the United States, most of our aggregate metropolitan area is auto-dependent suburban sprawl, and it’s not going away. Meanwhile, countries such as China and India are starting to replicate our bad land-use decisions. If anything, the need to retrofit suburbia is more urgent now than it was five years ago, when it seemed more buzz-worthy.

“Change is not only possible, change is necessary,” Williamson writes in her new book, Designing Suburban Futures: New Models From Build a Better Burb. Williamson and Dunham-Jones (who wrote the foreword) are still advocating for big changes in how we plan, design, and build in suburbia. It’s a testament to their success that the idea of a more urban suburbia has ceased to be controversial. Dunham-Jones tallies 460 retrofits in the database that she and Williamson keep, a huge increase—despite the wobbly economy—since Retrofitting Suburbia’s release.

In 2010, Williamson, who teaches architecture at the City College of New York, served as an adviser for Build a Better Burb, an ideas competition for transforming suburban Long Island. In her new book, she presents the winning entries. “SUB-HUB Transit System,” by Michael Piper and Frank Ruchala of Dub Studios, proposes a clever feeder transit system with public school substations—“subhubs”—funneling suburbanites to commuter trains. Another scheme, “Long Division,” by New York–based and Columbia University’s Network Architecture Lab, calls for densifying some parts of Long Island while de-densifying others to protect the underlying aquifer. The plans are sweeping and visionary, but also attainable: For example, Long Island’s first passive house, designed by Holler Architecture, is now under construction.

ARCHITECT spoke with Williamson and suburban visionaries such as Alexander D’Hooghe, who directs the Center for Advanced Urbanism at the Massachusetts Institute of Technology, and Garth Rockcastle, FAIA, of Meyer, Scherer & Rockcastle, to identify the top five reasons why the suburbs are shaping up as the new frontier.

1. NIMBYism isn’t what it used to be.
The most important legacy of Retrofitting Suburbia is that it won the war of ideas: By and large, Americans want their communities to be walkable and to have public amenities.

Sure, there are pockets of resistance, and adding density always sparks concerns about parking and traffic. But cultural stereotypes aside, suburbanites aren’t blinkered or in denial. Growth is a more attractive option than blight. “There’s less fear [now] of a backlash and closed ears in bringing up these topics,” Williamson .

In McAllen, Texas, Rockcastle’s firm turned a defunct Wal-Mart into an AIA Honor Award–winning public library; library-card registrations increased by a factor of 23. Dublin, Ohio, a small suburb of Columbus, is redeveloping 1,000 acres into a mixed-use center. “We need an area where people can stroll and hang out,” a local business leader told The Columbus Dispatch.

2. Cities alone can’t meet the demand for walkable urbanism.
Eighty-eight percent of Millennials say they want to live in an urban environment. Only there’s not enough urban space, traditionally defined, to accommodate them all. Even with infill development in cities such as New York and San Francisco, gentrification means that rents will remain out of reach for many. And don’t forget “job sprawl”: An increasing percentage of jobs are moving 10 or more miles away from the central business district. If you work in the suburbs, and downtown is expensive, then why commute?

Williamson hopes that “multicentric urbanism” will characterize the next generation of suburban redevelopment. In a given region, we might see multiple retrofits joined along a backbone of transit, with water management, flood risk, carbon sequestration, and other environmental strategies layered into the regional plan. Three strategies—reinhabitation of existing structures, redevelopment of dysfunctional parcels, and regreening of watersheds and wildlife corridors—must work in tandem and on a regional scale to achieve Williamson’s goal for North American metropolitan regions: “the gradual emergence … of a robust and efficient multicentered network of infilled centers and corridors [to replace] the pattern of ever-outward sprawl.”

3. Both policy changes and success stories can encourage investment.
Probably the biggest hurdles to rolling out creative, high-quality retrofits are financial and regulatory. Finance is inherently risk-averse; investors want to be sure of a return, so they stick with known quantities. In real estate, that means “asset classes,” a short menu of standardized development types (business hotel, big-box retail center) that are predominantly single-use. The Congress for the New Urbanism wants HUD, Fannie Mae, and Freddie Mac to recognize a wider variety of asset classes, which would make it easier and less expensive to finance mixed-use retrofits—critical for the movement to scale up.

More flexibility for financing could also give new life to the “live/work/play” formula that (re)developers now rely on. While first-generation retrofits often—and commendably—brought a mix of uses to single-use sites, they tended to rely on market-rate housing, ground-floor retail, and Class A office. For more resilient and more equitable suburbs, we need to diversify, Williamson says. She champions the kind of intriguing hybrids in the Long Island competition, such as an elderly housing/community center/botanical garden model proposed in “Long Division.”

D’Hooghe and Rockcastle believe that once there is a small body of successful next-generation retrofits, developers and investors will come around. Rockcastle compares suburban retrofits now to adaptive use of historic buildings 30 years ago. Just as that expanded from retail uses to offices to housing and beyond, the suburban retrofit will diversify and mature, he says. “The live/work/play paradigm might be the first inroad.”

Indeed, NAIOP, the trade association of U.S. office and industrial developers and owners, recently awarded a research grant to D’Hooghe’s firm, the Organization for Permanent Modernity, for a study on redeveloping middle-ring (or inner-ring) suburbs. It’s hard to imagine an American real estate trade group backing research by an OMA alumnus even five years ago.

4. Big boxes are awesome.
“I think [the big box has] got great, great potential” to transform the suburbs at scale, D’Hooghe says. “It’s so flexible, it’s so powerful. Even though I’m repulsed by it, in a way.” D’Hooghe nevertheless mounts an aesthetic defense of the vulgar box as “the realization … of the promise of absolute abstraction, in terms of flatness, horizontality, lack of expression, [and] lack of authorship.”

Don’t think of your local Petco: Imagine a new kind of box, a “high-quality exoskeleton that can house almost any function.” D’Hooghe’s master plan for a district of Brussels frames an urban square with three- or four-story boxes that have “towerettes” of eight or more stories, a gesture to historic warehouse buildings nearby. The boxes can be used first as parking, then can be converted into office or loft space, a phased concept that D’Hooghe and his team also employ in their middle-ring NAIOP study. In Asse, a Brussels suburb, D’Hooghe has designed a single linear big box to house the town’s fire station and youth center.

5. Suburbia’s fabric lends itself to innovation. We tend to think of suburbia as a stable monoculture of tract housing. Not so, says Rockcastle: “The great opportunity in the suburbs is it’s a looser matrix that allows more experimentation and divergence,” he says. (Are you listening, tactical urbanists?)

Paved expanses and hostile pedestrian conditions cry out for some landscape-urbanist TLC. There is a pressing need for new housing types as households shrink and families with children become a minority. Many of the communities at risk from storm surges and other climate effects are suburban in form; efforts to make homes and neighborhoods more resilient could well generate new suburban typologies as a byproduct.

Of course, there’s the patchwork of private ownership to contend with. Owners large and small have little incentive to improve the spaces in between their properties. What are now fissures could become greenways or bioswales, but that will require close collaboration among local governments, owners, developers, planners, designers, and citizens. Land-use reform, like financial reform, needs not only incentives, but also “sticks” such as inclusionary zoning, green building standards, and stormwater regulations.

Fifty percent of the U.S. population lives in suburbs. The most diverse neighborhoods in the country are suburban. There are more old and poor suburbanites than ever before. Architects need to engage with these issues, otherwise, Williamson warns, “they risk becoming increasingly irrelevant.”