Imagine a world in which every apartment is required by law to include accommodation for around-the-clock butler services. In this world, developers would have to add an additional 9×19-foot room to every single unit–at a cost between $40,000 and $50,000–even if the apartment is being built for working-class people who could never afford the butler to go with the room. To ward off a future shortage of butler housing, regulators also made it illegal to use the butler’s quarters for any other purpose, whether or not the tenants actually hired a live-in butler.

Most people would say a requirement for live-in butler quarters is obviously a bad idea, and that it would increase the cost of housing without providing any real benefit. It would waste precious space and developers would have an incentive to only build high-end units to make up for the cost of building amenities that few people actually use.

Washington, D.C. has a policy similar to the fanciful rule above: parking minimums. Depending on where a project is located, and what the building will be used for, local regulations require developers to build a certain number of parking spots for every unit in a building. This is bad news for affordable housing advocates for several reasons.

The most obvious way it hurts renters is outlined above. That is, it forces developers to build units with an expensive amenity attached that potential customers might not need. As Donald Shoup and others have found, building an underground parking space costs between $40,000 and $50,000. Whether tenants use those parking spots or not, they’re going to have to pay for them in the form of rent.

Parking minimums also serve as de facto limits on density. Leaving aside the effects of the Height Act, local zoning keeps buildings to a significantly lower height limit in large parts of the city. That means developers either have to set aside a large part of their lot for surface parking, or they have to dig and build underground spots. These constraints often lead developers to build smaller projects than they otherwise would.

Minimums also change the incentives when developers are determining the price level and size of units they build. When every unit must come with an expensive amenity, developers can reduce the number of parking spaces they have to provide by building larger, more expensive, multi-room units. It also creates an incentive for developers to build luxury apartments or condos to recoup the cost of building spots.

One way to avoid these perverse incentives is to eliminate parking minimums for residential development. Since developers are primarily trying to maximize their profits, they have a strong incentive to provide the right amount of parking for their project. If they think future tenants are willing to pay for parking spaces, then they’ll build them. Then-Director of the  Office of Planning Harriet Tregoning proposed this exact reform for transit zones last year, but backed down in the face of vocal public opposition.

People who oppose lower parking minimums usually do not want to compete with additional drivers trying to store their cars on public streets. Assuming their objection is valid, it can be easily addressed: eliminate parking minimums for units designated for low-income residents who are less likely to own a car. The district government should reduce the number of parking spots required for any given real estate project in proportion to the number of “affordable units” the developer is required to build under current inclusionary zoning rules.

That is, if regulations require a developer to build one parking spot for every two units, the developer should be able to subtract one parking spot from the required parking minimum for every two affordable units in a proposed building. Such a rule would allow developers to forgo a large capital expenditure that is unlikely ever to be used. After all, a person who can’t afford a card doesn’t need a parking spot, and an empty space in a parking garage doesn’t make it any easier to park on the street.

As of now, developers are sometimes able to receive a variance from current zoning rules if they take a loss on affordable units in exchange for greater allowed density. Reducing the number of parking spots developers are required to build in proportion to the number of affordable units in a building simultaneously increases the supply of housing, and helps to offset the problems created by parking minimums and inclusionary zoning itself.

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