Ever since he won election in 2013, New York City Mayor Bill DeBlasio has talked a lot about affordable housing. On Friday afternoon his administration rolled out its most promising initiative on this yet — a broad change to the city's zoning code that should allow for the construction of housing units.

DeBlasio's plan

The proposed reform has three main elements:

Reduces parking requirements for senior or low-income housing Allows taller buildings Allows more flexibility in designing housing for senior citizens

None of this alters the key zoning metric known as Floor Area Ratio, which is the ratio of built-out floorspace to total land occupied. In other words, if you have 6000 square feet of apartments sitting on top of a 2000 square foot lot, you have an FAR of 3. But it all works together to make it considerably cheaper and easier for developers to craft structures that maximize the permitted floor area ratio.

Parking: Currently, outside of central Manhattan essentially all new buildings in New York City are required to include new parking spaces — driving up the cost of real estate in a city where land is extremely scarce. DeBlasio is proposing to eliminate minimum parking space regulations for senior citizen or low-income housing if it is either near a subway station or includes access to an off-site parking facility. He is also proposing to reduce the amount of parking required for senior citizen or low-income housing even if it's far from transit. Last, he wants to "create a process to allow, where appropriate and on a case-by-case basis, reduction of parking requirements to facilitate mixed-income development, or affordable housing developments with existing underutilized parking facilities to be redeveloped."

Building height: DeBlasio is proposing, essentially, that developers should have the flexibility to build structures that are tall enough to reach the maximum FAR allowed. Currently, height restrictions are often poorly matched to FAR rules. A zone might allow for an FAR of 5.0 but also prohibit buildings that are tall enough to achieve this in a sensible way. At best, developers can make it work by employing either short ceilings or very boxy buildings with no setbacks or courtyards. At worst, they simply don't build out to the maximum FAR. This is especially important because current law offers developers FAR bonuses for including affordable housing in their projects. Often, however, height limits make it impossible to take advantage of this opportunity. The new rules should increase the production of both subsidized and market rate housing.

Senior housing: DeBlasio is proposing to allow more flexibility in terms of combining nursing home units with other types of senior-focused housing, as well as easing the permit process to get permission to build assisted living units.

Big gains, more could be done

These are very positive steps to address a huge problem that costs the American economy billions of dollars in output each year. But of course New York City could go further. Regulatory mandates that new buildings include parking spaces, for example, are no more reasonable for market rate housing than for subsidized affordable units.

More to the point, even though New York City is the country's largest city, it is only a relatively small slice of the overall affordable housing problem. Most residents of Greater New York, and of every other metropolitan area, live in suburban jurisdictions where the anti-affordability rules are generally even more severe. Tackling the nationwide affordability crisis will ultimately require zoning relaxation not just in New York, but in central cities and their suburbs up and down both coasts.