Affordable housing policies have a long history of hurting the very people they are said to help. Past decades’ practices of building Corbusian public housing that concentrates low-income people in environments that support crime or pursuing “slum clearance” to eliminate housing deemed to be substandard have largely been abandoned by housing affordability advocates for the obvious harm that they cause stated beneficiaries. While rent control remains an important feature of the housing market in New York and San Francisco, even Bill de Blasio’s deputy mayor acknowledges the negative consequences of strong rent control policies. In the U.S. and abroad, politicians and pundits are beginning to vocalize the fact that maintaining and improving housing affordability requires housing supply to increase in response to demand increases.

While support for older housing affordability policies has dissipated, the same isn’t true of inclusionary zoning. From New York to California, housing affordability advocates tout IZ as a cornerstone of successful housing policy. IZ has emerged as the affordable housing policy of choice because it has the benefit of supporting socioeconomic diversity, and its costs are opaque and dispersed over many people. However, IZ has several key downsides including these hidden costs and a failure to meaningfully address housing affordability for a significant number of people. Shaila Dewan of the New York Times captures the strangeness of IZ’s popularity:

New York needs more than 300,000 units by 2030. By contrast, inclusionary zoning, a celebrated policy solution that requires developers to set aside units for working and low-income families, has created a measly 2,800 affordable apartments in New York since 2005.

Montgomery County, a Maryland suburb of DC, has perhaps the most well-established IZ policy in the country. After 30 years, the program has produced about 13,000 units. Montgomery County is home to over one million people, 20 percent of whom have a household income of less than $43,000 annually. While this is an extraordinarily high income distribution relative to the rest of the country, this makes the county’s median apartment rental of nearly $2,300 out of reach for many more people than even an aggressive IZ policy can serve.

While Montgomery County’s IZ housing does not reach a large percent of its population, it has provided many more units than other cities’ programs have. Washington, DC’s IZ law was passed in 2006, requiring developers to set aside 8-10% of units as affordable in all new projects with more than 10 units. As of the most recent 2012 report, DC’s IZ program has yet to reach a single beneficiary. The IZ units that have made it to market are sitting empty. This is in part because IZ units, priced to be affordable to those making between 50% and 80% of the Area Median Income, are not the most cost effective choice for many people in this income range, potential beneficiaries of owner-occupied IZ units may not be able to qualify for a mortgage. IZ units tend to be one- or two-bedroom apartments. Low- and moderate-income DC residents may be able to find housing that is much more affordable than what IZ provides by living in a larger apartment with a roommate(s), in a group house, or with family. By attaching these affordable units to new, often luxury buildings, IZ siphons affordable housing resources to the type of housing where it will buy the least.

Evidence on the benefits that mixed-income housing provides for low-income people is mixed, but it’s hard to deny that inclusionary zoning beneficiaries win a lottery. They live in new construction in desirable neighborhoods, housing that would cost several times as much at the market rate. However, IZ’s effects are not limited to beneficiaries, and its costs are not fully borne by developers. Because developers will lose money on the IZ units they build, this cost has to be made up in the market rate units in order for the project to go forward. This adds to construction costs and also incentivizes luxury units that can better absorb the cost of the IZ units relative to more affordable construction. While providing affordable housing to a few lucky low-income people, IZ also makes housing less affordable for everyone who doesn’t receive the benefit by reducing housing supply and skewing the market toward luxury housing that can subsidize the affordable units.

IZ appears free to everyone except developers because it’s not paid for out of city budgets. But ultimately housing consumers share in the cost of IZ units through a hidden tax. By making new construction more expensive, IZ also reduces the rate at which the prices of older or less desirable housing filters down to the point that it becomes affordable to low- and middle-income residents. Putting affordable housing in new construction ensures that it will benefit fewer people than the same amount of resources otherwise could. IZ supporters emphasize the importance of neighborhoods that are socioeconomically diverse but ignore the opportunity cost. Low-income people may be well-served by putting resources toward living in a diverse neighborhood, but this competes against many other places their resources could go, including investing in a business, pursuing education, or prioritizing nutritious food.

As economist Ben Powell explains, IZ can be designed not to have an effect on market-rate housing prices if developers are allowed to voluntarily trade the provision of IZ units for density bonuses. In that case the bonuses must be high enough to offset the cost of the below-cost units. However, as Stephen has pointed out, IZ creates an affordable housing lobby that opposes upzoning without affordability requirements. Eliminating IZ would put all housing affordability advocates on the same team. The same amount of resources currently providing for IZ units could be levied as a transparent tax and transferred to low-income people as cash rather than as luxury housing. This would also allow for resources to be distributed based on need, rather than giving a few households a jackpot.