An important new study was released today by the Citizens Housing and Planning Council, finding that we could add between 10,000 and 38,000 basement apartments in New York City using existing housing stock. In a city with a constant housing crisis and high construction costs, finding these types of hidden housing will be vitally important to making sure we have enough homes and maintaining New York City as affordable for a wide range of people.

It’s important to note that the 10,000 – 38,000 potential basement apartments is just the start of possibilities for adding additional housing without adding to the built environment. For instance, it doesn’t examine possible basements apartments in two- or three-family homes, or other parts of a house - such as attics, cellars, or garages – which could be converted. While legalizing these apartments is more difficult, and would need significant revisions of the multiple dwelling law, zoning regulations and other rules to become practical, they could add hundreds of thousands of new homes to New York City, increasing the existing housing stock by almost 10% without laying a single brick.

And in addition, much of our above-ground rules need to be reformed. We have neighborhoods within walking distance of the subway that only allow single family McMansions to be built, instead of two duplexes which would provide four times as many homes in the same building envelope or permitting the subdivisions of McMansions themselves. And there are tens of thousands of homes throughout the five boroughs which are used as pied-a-terre housing or taken off the market for Air BnBs, which could be encouraged through the legal, tax or building codes to instead to become full-time housing for New York City residents. In Manhattan alone, if all of the homes which are off the market as part-time housing were instead available for rent to full-time New Yorkers, the vacancy rate would be 11.3%.

We need to build more. But, as shown by CHPC, we also need to use what we have in a better way.