SAO PAULO, Brazil — As shoppers and businessmen pass by the 13-story office tower, a middle-aged man peers through a hole in a thick metal door, pulling back a heavy steel rod to allow in only members of the Movement of Housing for All.

Upstairs, children, low-income workers and a few revolutionary idealists squat in makeshift apartments that boast stunning views but no water or kitchens. Communal bathrooms are available in the middle of the Sao Manuel office building, which has been occupied by the movement for almost a year.

In a large central room, a group of women prepares a cheap, hearty meal and plans out a work schedule for fellow residents. When an 80-year-old woman with diabetes falls ill, others on her floor come together to call paramedics. When she dies in the hallway, the neighbors comfort one another before moving on with their lives.

"I came to Sao Paulo from my small hometown, where there is no work, and ended up staying in this occupation with a friend without knowing anything about it at all," says Mirla Kelly Firmino da Silva, 22, a freelance beautician who specializes in manicures. "But now I believe completely in the movement. None of us can afford to pay what rent costs here, and we deserve dignified housing."

Over the last year, the center of South America's largest city has been markedly transformed, with nearly 50 abandoned buildings occupied by squatters from Brazil's many sem-teto, or roofless, movements.

The occupation protests at the buildings, where red flags hang from windows, are meant to pressure the government to provide adequate housing and give working families a place to live.

In both rich and poor neighborhoods of Sao Paulo, a metropolis of 11 million, property values have more than doubled in the last four years, leading to increased housing costs for those least able to afford them. In the seedier parts of downtown, a tiny one-bedroom apartment overlooking scenes of drug use and prostitution costs $450 a month; meanwhile, the minimum wage is $310 a month.

At Sao Manuel, known locally as the Marconi occupation after the street that the building is on, 140 families each pay $50 a month and work a few hours per week, manning the front door, cooking or cleaning.

Occupations of long-abandoned buildings began here more than a decade ago, but the rising cost of living and a relatively sympathetic city government have led to a recent surge.

According to the city of Sao Paulo, there are at least 4,000 families living in occupied buildings in the city center alone. The MTST, a larger sem-teto organization, says it has at least 600 additional occupied plots of land in the state and 10,000 people on a waiting list to occupy more.

"There will be an explosion of occupations over the next few years," predicts Guilherme Boulos, national coordinator for the MTST, who met with President Dilma Rousseff during a wave of economic and social protests in June. "We told her the only way to create a sustainable housing policy in Brazil is to stop the rise in housing prices."

At the local level in Sao Paulo, the recently installed city government from Rousseff's ruling Workers' Party has a complicated relationship with the occupiers.

"It is a legitimate form of social protest," city Housing Secretary Jose Floriano de Azevedo Marques Neto said at his office a few blocks from the occupation, before conceding that, "Yes, they are illegal."

When police catch groups breaking into abandoned buildings, they make arrests. But squatters, once inside, can remain until expelled by legal proceedings, and in the meantime can use their position to pressure the government to expropriate the properties from the owners who abandoned them and often owe back taxes. Occupiers often get on the government's list to receive subsidized housing.

Floriano de Azevedo's office says it plans to build 55,000 homes, but estimates the city needs at least 230,000 units. According to government estimates, the country as a whole is in need of more than 5 million additional homes, mostly in urban centers.

Many of the occupied buildings were abandoned years ago, long before the economic boom that has transformed Brazilian cities into havens for the rich, as well as increasingly tough places for the poor to survive.

Since many owners of abandoned buildings owe back taxes, they have not returned to clean up and reuse their properties.

Constructing housing for Brazil's poor is not profitable enough for private firms, says Claudio Bernardes, president of the real estate industry union in Sao Paulo. At the same time, he says, the occupations are illegal, and building owners have turned to the courts to regain their properties. No ruling has yet been made as to when the Sao Manuel protesters would have to leave. We "cannot accept a form of protest that infringes on the rights of others," says Bernardes.

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At a weekly meeting at the Sao Manuel occupation, coordinators announce the names of those who have been expelled from the occupation for improper behavior, and run through lists of costs and legal victories.