Economic inequality is one of the most significant issues facing cities and entire nations today. But a mounting body of research suggests that housing inequality may well be the biggest contributor to our economic divides.Thomas Piketty’s influential book, Capital in the Twenty-First Century, put economic inequality—and specifically, wealth inequality—front and center in the global conversation. But research by Matthew Rognlie found that housing inequality (that is, how much more expensive some houses are than others) is the key factor in rising wealth.

Rognlie’s research documented that the share of wealth or capital income derived from housing has grown significantly since around 1950, and substantially more than for other forms of capital. In other words, those uber-expensive penthouses, luxury townhomes, and other real estate holdings in superstar cities like London and New York amount to a “physical manifestation” of Piketty’s insights into wealth inequality, as Felix Salmon so aptly puts it.

More recent research on this topic by urban economists David Albouyand Mike Zabek documents the surge in housing inequality in the United States. Their study, published as a National Bureau of Economic Research working paper, charts the rise in housing inequality across the U.S. from the onset of the Great Depression in 1930 through the great suburban boom of the 1950s, 1960s, and 1970s, to the more recent back-to-the-city movement, the 2008 economic crash, and the subsequent recovery, up to 2012. They use data from the U.S. Census on both homeowners and renters.Over the period studied, the share of owner-occupied housing rose from less than half (45 percent) to nearly two-thirds (65 percent), although it has leveled off somewhat since then. The median cost of a home tripled in real dollar terms, according to their analysis. Housing now represents a huge share of America’s total consumption, comprising roughly 40 percent of the U.S. total capital stock, and two-thirds of the wealth held by the middle class.

What Albouy and Zabek find is a clear U-shaped pattern in housing inequality (measured in terms of housing values) over this 80-year period. Housing inequality was high in 1930 at the onset of the Depression. It then declined, alongside income inequality, during the Great Compression and suburban boom of the 1950s and 1960s. It started to creep back up again after the 1970s. There was a huge spike by the 1990s, followed by a leveling off in 2000, and then another significant spike by 2012, in the wake of the recovery from the economic crisis of 2008 and the accelerating back-to-the-city movement.

By 2012, the level of housing inequality in the U.S. looked much the same as it did in the ’30s. Now as then, the most expensive 20 percent of owner-occupied homes account for more than half of total U.S. housing value.Rents show a different pattern. Rent inequality—or the gap between the cost of rent for some relative than others—was high in the 1930s, then declined dramatically until around 1960. Starting in about 1980, it began to increase gradually, but much less than housing inequality (based on owner-occupied homes) or income inequality. And much of this small rise in rental inequality seems to stem from expensive rental units in very expensive cities.

The study suggests this less severe pattern of rent inequality may be the result of measures like rent control and other affordable housing programs to assist lower-income renters, especially in expensive cities such as New York and San Francisco.

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