As Detroit carries out its plan to tear down tens of thousands of homes to combat blight and tailor the city to fit its population, which has dwindled to about a third the size of its 1950s peak, it will have to deal with an unknown number of squatters.

About 10 percent of the houses Adamo Demolition goes out to demolish have squatters or evidence of squatters, according to Mathews.

Chris Mathews' crew showed up to demolish a vacant home as part of Detroit's grand plan to bulldoze its way to prosperity when a call from his office stopped them in their tracks: Someone was living there.

A middle-aged woman who watched the crew tear away the home's warped wooden steps the day before had called their company, Adamo Demolition, to point out she was living on the second floor, despite no power, heat or gas and a flooded basement.

"It was like a swimming pool. We would never have thought anybody was upstairs," said Mathews, noting that the incident cost his crew time because the demolition wasn't called off until after they had shown up with their equipment.

Since the city doesn't allow occupied properties to be demolished, squatters who won't leave voluntarily and who have no previous connection to the homes have to be removed by police for violating the city's trespassing laws. That makes them a complication of sorts for the recovery of the city, which emerged in December from the largest municipal bankruptcy in U.S. history.

A survey completed last year determined that more than 40,000 structures needed to be torn down. Another 38,000 had indications of blight and could be up for demolition. Clearing away as many vacant houses as possible as quickly as possible is a priority. Drug dealers often set up shop in them, bodies turn up in them and some houses have been sites of sexual assaults.

But for some of the approximately 16,000 homeless people in Detroit, the structures offer safety and shelter.

Michele McCray calls them "abandonminiums." McCray, 58, has been homeless for much of her adult life, yet she has had her pick of vacant houses to live in over the years.

"You look for one that's decent, already fixed up," McCray said from a homeless shelter where she stays when it's too cold to hunker down in a house without heat and other utilities.

"The first thing you do is cut the grass ... because the neighbours want to know who you are and what's going on over here. You have to maintain the property. Paint the place up, keep it looking good."

She sees it as a community service.

"A lot of people leave the door open because they want somebody to move in there," McCray said. "When you got somebody that's living in a place ... that keeps people from coming in, tearing the place up, stealing the fixtures. It cuts down on people starting places on fires, stealing your furnace."