NEW YORK (CBSNewYork) — New York City is in the middle of a housing boom.

Over the first six months of 2015, developers received more than 42,000 building permits for apartments and houses, according to the U.S. Census Bureau. That number outpaces any full year since 1963.

Michael Slattery, senior vice president of the Real Estate Board of New York, called the surge “staggering.”

He said the impetus for the wave of activity is the June 15 expiration date of a valuable property tax abatement, called 421a, and changes in the rules.

Under “the new program, there will be no place in the city of New York, where you can building with a 421a extemption without providing affordable housing, and those affordable-housing percentages have gone from 20 percent to 25, in some cases 30 percent,” Slattery explained.

Those changes, he noted, caused developers to act sooner rather than later.