What is the solution to affordable housing in New York?

One number has been repeated over and over — 200,000 subsidized units, to be built or preserved over a decade. Mayor Bill de Blasio promised it, but has yet to explain how he’ll get there.

Here are two other numbers: 9 x 18. In square feet, that’s 162, smaller than the most micro micro-apartment.

It is the size of a typical parking space. That lowly slice of asphalt has prompted three young architects — Miriam Peterson, Sagi Golan and Nathan Rich, fellows at the Institute for Public Architecture — to come up with what could be an innovative way to ease the housing crisis.

I’m intrigued by their proposal, “9 x 18,” because it’s about more than apartment buildings plopped onto vacant land. It considers how parking spaces — mandated in outmoded zoning regulations, prolific at public housing sites — might be leveraged into something more ambitious, something that encourages a mix of housing in active neighborhoods with accessible transit, public services and lively streets. In effect, the proposal trades asphalt for housing and amenities.