Mayor Bill de Blasio’s attention to big progressive causes hasn’t always borne fruit. But with affordable housing, he’s made a dent, one with real-life implications for hundreds of thousands of New Yorkers.

The de Blasio administration has created, preserved or financed nearly 78,000 units of housing in three years — more than any other mayor over the same amount of time.

The key piece of the statistical puzzle involves the 25,000 units created or preserved in the last year. Of those, 43 percent — more than 10,000 — went to New Yorkers earning $30,000 or less. That means NYC finally has begun to provide affordable housing for those who need it most: those skating along the edge between keeping their apartments and ending up homeless.

It’s a good start, but de Blasio is still far from the goal line.

The city’s shelter census continues to hover above 58,000 a day. Of those, 22,000 are children. And there are many city residents who aren’t homeless, but live in housing that’s far more expensive than they can afford. We cannot remain a city where any of that’s the norm.

What’s more, about two-thirds of the 78,000 housing units de Blasio touts involves preservation, when the city finds ways to keep housing affordable even as market rents rise. That’s important, but there has to be an effort to add more new housing. Even then, the city has to make community improvements to go along with new homes, such as adding schools, parks and other infrastructure.

The good news is that de Blasio’s “mandatory inclusionary housing” program is still in its infancy, so more housing should be built soon. The bad news is that too often, City Council members object to such zoning in their districts. And even when there’s support, the process is too slow.

The next year is an important one. De Blasio can’t rest on his laurels now or if he’s re-elected in the fall. He has to show his signature program can create significant new housing, especially for those earning lower incomes, while still meeting each community’s needs as that housing becomes available, neighborhoods change and populations grow. And all City Council members should support such efforts despite potential local opposition.

De Blasio has laid the foundation for a city committed to housing all of its residents. Now, he has to build on it.