Six months since Rogers Place opened in downtown Edmonton, the city's new arena is in need of repairs.

Nine exhaust fans on the building's roof have to be replaced after a piece of one of the units broke off and landed in a nearby construction site.

"When a fan cracks — a fan blade cracks — you can hear it, and there was a noise that we heard," Rick Daviss, executive director of the downtown arena project for the City of Edmonton, said at a news conference at city hall Thursday.

"Certainly when one fell off the roof, it pointed out in spades that we had a real major concern and not just a minor concern."

No one was harmed and there was no risk to public safety, Daviss said.

Three of the existing fans will remain in place while the nine faulty units are removed. "We feel that three of them will be fine," Daviss said.

"There's been breakages, fan blades have cracked, we've had housings damaged — they're just not working the way we thought they would."

A large crane will be required to remove the fan units from the roof and lift their replacements into place.

That will mean ongoing lane closures on the streets around the arena, beginning the week of March 20 and lasting three to four days.