School custodians are cleaning up — in the hallways and in their paychecks — because the city doesn’t want to hire enough of them.

Custodians took home an average pay of $109,467 in the 2013-14 school year — and 634 of the city’s 799 custodians earned more than $100,000 in salary and overtime during that time, city payroll records show.

That’s because of the city’s 1,500 school buildings, 238 have no full-time custodian on site, up 74 percent from the 137 empty slots in 2012, according to data from the custodians union.

The arrangement is forcing nearly one-third of the city’s 737 custodians to cover two schools — and reap additional pay.

Union leaders say the city has traded school cleanliness and safety for a meager savings.

“The city is not saving much money because they’re paying my members to be at both places,” said International Union of Operating Engineers Local 891 president Robert Troeller, referring to overtime costs. “I don’t know why they’re not hiring. It’s ridiculous.”

Custodians possess licenses needed to operate and maintain a school building, including credentials for boilers, heating/air conditioning and fire sprinklers and alarms.

Department of Education spokesman Jason Fink said school buildings have “fully qualified” staff members on site who can perform all duties required.