The next time you fly into DFW airport, have a look out the window. Somewhere down there—it could be Argyle or Double Oak or anywhere on the periphery of the North Texas sprawl—you’ll see half-built neighborhoods that look as if the assembly line simply stopped rolling. With names like Rambling Meadows, the developments have arbitrarily curved streets lined with tract homes, one after another. Different addresses, same house. What will become of these places in 20 years? How about 50?

Quality, or lack thereof, is a major concern. The houses that sprung up near Sun Belt ring roads like algal blooms were not built to last. I have an architect friend named Robb Davis, of Frank Welch & Associates, who specializes in custom-built single-family homes. He tells me that in order to get houses up in three months rather than 12 to 18, builders use stock plans without giving much thought to layout. Rooms are huge because that means fewer walls, and walls cost money. The lumber is full of knots, and it’s softer than the old-growth timbers that were used to build houses 50 or 100 years ago. The result is that much of the tract housing stock in our exurbs won’t be standing in 30 years.

And there’s lots of it. The current supply of 4,000-square-foot multigabled brick houses vastly outstrips demand, particularly in areas where the house is “affordable” because transportation costs and upkeep have been ignored. Professor Arthur Nelson, director of the Metropolitan Research Center and professor of city and metropolitan planning at the University of Utah, expects a country-wide (pun intended) surplus of 22 million large-lot homes by 2025.

To examine the supply-demand imbalance and its effect on price, I looked into the fluctuations in assessed value of one of the best exurban developments in North Texas, Craig Ranch. The master-planned community in McKinney has every amenity anybody could possibly want. TPC golf course, check. Parks and trails, check. Michael Johnson training center, check. Town center—well, kind of. Still, Craig Ranch is the sort of development that makes New Urbanists salivate.

Using the Collin County assessor’s website, I looked at five representative properties in Craig Ranch. They lost an average of 44 percent in total value, including “improvement” (aka house) and land, between the 2008 housing peak and 2011. Certainly some measure of the loss is due to the funny money floating around in the market, but there is a locational correction at work as well.

Next, I looked at a number of houses on Swiss Avenue, near downtown Dallas, paying attention to larger houses of comparable size to those in McKinney. Also of interest were properties that had been converted into multifamily dwellings, as many New Urbanists think the same transition might happen to McMansions in outlying areas.

Interestingly, the overall assessment of the Swiss Avenue properties went up in all cases but one, which remained flat. Tossing out one outlier, a property that more than doubled, the others averaged a 10 percent increase in value since the housing peak in 2008. For some of these properties, the structure’s value actually dropped as the land value climbed, in some cases nearly tripling since 2008.

It isn’t just the Swiss Avenue properties that are holding steady. The English Tudor homes in Hollywood Heights, the craftsman cottages along the M Streets, the eclectic houses of Junius Heights—none of them have taken a 40 percent dive like the places in McKinney.

A house is first a home. It’s only an investment when it is passed between generations. A house in the center of Amsterdam costs the same today as it did 400 years ago, when adjusted for inflation. Of course, the next generation has to see value before it will bother to care for the property. The houses along Swiss Avenue, like those in Amsterdam, received some TLC 60 or so years into their life spans.

To last that long, a house needs to be useful, adaptable, and, most important, loved. I’m afraid many exurban neighborhoods, most built to standards far below those of Craig Ranch, face an uncertain future against shifting demographics looking to downsize. What we need most is a more comprehensive understanding of what affordability means. Perhaps we trade some of that excess space for durable, well-crafted houses located in complete neighborhoods. The oversize pantry is externalized as the corner market, the third garage is replaced by a gaggle of bikes, the rec room becomes the neighborhood, and the dining room, its restaurants.

At some point, adolescents stop growing up physically, and they start maturing. Growth is internal, intellectual, and emotional. Qualitative. It’s time for the Sun Belt (and the financial mechanisms that built it) to grow up, not just out.

Write to [email protected].