Pay no attention to the images of skeletal subdivisions abandoned in the face of high gas prices (remember those?) and the burst housing bubble: Suburbia is not dead. It’s not even dying. Half of all Americans live in suburban areas, and 40 percent of American jobs are rooted there.

But our suburbs are unsustainable, and not because we’ve rediscovered the joys of urban dwelling and a connection between vehicle miles traveled and quality of life … and air. In fact, the greatest threat to suburbs over the next decade is this: “There might not be enough people to live in them.”

So says June Williamson, author of Retrofitting Suburbia. In the 1950s, 50 percent of American households had children. Now, says Williamson, that percentage has shrunk to 35; by 2030, it’ll be down to 25 percent. Without families to fill those McMansions, suburbs will need new housing types for retirees who want to downsize and grown children who wish to remain close to home (though this unearthed article has one housewife comparing suburbia to jail). Not all those folks want to shift into urban centers, or can afford to. So suburbia is due for a massive makeover. Yes, it’s time for a retrofit.

Those big houses on big lots, housing only a few people, those single-story strip malls, those vast tracts of virgin land snatched up to make parking lots all represent the great potential for redevelopment. Williamson and co-author Ellen Dunham-Jones’ thesis: Take the sub out of suburb, so it’s not a subspecies of the city but its own viable, mixed-use, higher density locale. They call it “incremental metropolitanism.”

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One way to incrementally metropolitanize an area is to allow a variety of housing types. Easier said than done. Most towns or subdivisions have zoning laws or covenants that prevent more than one dwelling unit on a lot, but a number of forward-thinking places allow accessory dwelling units — that’s mother-in-law apartment to you and me. Seattle, for instance, has legalized granny flats, allowing a single 1,000-square-foot accessory if that unit, or the original house, is owner-occupied and there’s off street parking. In Levittown, N.Y., largely thought of as our first suburb, the surrounding town allows what they call “Mother/Daughter Use,” meaning a second kitchen can be added to a home, and “Two-Family Senior Residence,” allowing an additional unit to be built and rented to someone over 62. And some forward-thinking residents are taking matter into their own hands: Neighbors in Sandy Springs, Ga., banded together to sell their entire housing stock to a developer, who razed and reinvented it as high density homes.

Housing is only one suburban element in need of retrofit. There’s transit, of course — even if many of these areas started as “streetcar” suburbs, the streetcars are long gone, leaving only regular old cars to replace them. And then there’s retail.

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The problem is scale: One developer owns and controls an entire strip or shopping center, so that individuals can’t effect change. In many a shopping mall, the closing of an anchor store gives the whole center what Williamson calls “the whiff of failure.” Admittedly, due to the economic crisis, some malls have been lowering rents to coax local clients. But bending to accommodate locals isn’t enough. Instead, she proposes, “Large sites can be broken up into smaller blocks of mixed uses, so it can be more adaptive over time, and operate more like a real neighborhood, where if one business fails, the whole thing doesn’t fail.”

Such was the case at the Cinderella City Mall in a suburb of Denver. Failing, like many of the regional malls around that city, it was redeveloped to include Englewood City Hall, 440 apartments, almost 500,000 square feet of office and retail space (ok, some of that is a Wal-Mart), and a light-rail station. Yes, they made a mall into a mini-city, with public-private partnerships and individually owned and operated elements — and it seems to have worked.

Some may wonder if turning a shopping mall into a town and turning a suburb into a city is the best solution. Do we want density — highrises and light rail and commercial districts — everywhere? Want, says Williamson, is not relevant. There’s going to be growth, and it can either be healthy or sick. And what would happen if we didn’t retrofit, shift and change along with our demographics? Williamson has no answer for that. “I can’t see it not happening,” she says. “It really is just a question of degree — how much retrofitting and where — and quality: how good will the retrofits be.”