Philadelphia is falling. Marble, bricks, and concrete from at least three mid-rises cracked the sidewalks on busy Chestnut and Walnut Streets last summer, recalling pavement-shattering events like the Lafayette Building cornice that fell onto Fifth Street in 2001, and the Broad Street facade that fell on a city judge, killing him, four years earlier.

After each rain of stone, city officials and building owners debated the need for mandatory facade inspections, as they have in New York and Chicago. They decided against it - until now.

In February, City Council unanimously approved, and Mayor Nutter signed, an ordinance for mandatory five-year inspections and repairs to buildings six stories and higher.

Besides its safety merits, the law gives extra work to engineers, architects, and building crews. Idled by the slow economy, they crowded a meeting with building owners hosted by the city Department of Licenses and Inspections last month, in hopes of picking up jobs.

Buildings put up before 1951 have to be checked by next June; newer buildings get more time. Donald Haas, who manages the Bell Atlantic tower and headed the Building Owners and Managers Association of Philadelphia during negotiations over the law last year, estimates the cost at "anywhere from $15,000 up to $50,000 every five years" for an office high-rise, maybe a few thousand less for a six-story apartment building.

Haas' members are footing the bill, yet they ended up supporting forced inspections - after winning an extension to cover buildings as low as 60 feet, to what was originally a bill focusing on high-rise towers only. Tower owners pointed out that many of the problems originate with older, lower buildings, which, in Philadelphia, often compete with high-rises for small-office tenants.

"Our members define the skyline of Philadelphia, and the worst thing we can have is you guys writing something fell off one of our buildings," Haas told me. "We were one of the few cities that didn't have a facade ordinance. You could make a strong case we didn't need one if it is in L&I's property-maintenance code. But the code is reactive; people check it when somebody makes a complaint. This is proactive [catching loose material before it slips to the street]."

What goes wrong? "A lot of Philadelphia buildings are masonry limestone [like City Hall], or brick, like Independence Hall, or terra cotta, like you have at Drexel," structural engineer Mark A. Coggin, a principal at Thornton Tomasetti Inc.'s Philadelphia office, told me.

Those materials allowed attractive ornamentation, "but they're brittle," Coggin explained, "and some are hollow inside. Cracks open, water freezes and pushes the joints apart. Like at the Lafayette Building [at Fifth and Chestnut]." Depression-era towers may have "loose cladding, anchorages that corrode, panels that fall off," he said.

Glass and steel panels on newer high-rise buildings are typically well-anchored, but metal handrails and balconies tend to corrode at the base, and many in New York's older buildings have been declared unsafe, Coggin said.

His colleague, senior associate William Lukens, gave me a copy of the one-page form the firm uses in its New York inspections, and the detailed reports and recommendations to comply with city codes and to keep building fronts in the air, where they belong.

Building manager Haas credits the Philadelphia bill's sponsors, Councilmen Jim Kenney and Frank DiCicco, with "getting all the interested parties together - architects, engineers, contractors, building owners."

Why now? "When more pieces started falling off the buildings, it was time," Kenney told me. He blamed the Philly- is-New-Orleans-in-summer effect: "We're especially vulnerable here because we sit between two rivers, we're pretty damp and humid, and the iron that holds the masonry on tends to rust and separate from the building," Kenney said.

Council has not estimated the cost of inspecting and fixing city-owned buildings. Kenney noted the Philadelphia School District "has lots of buildings that fall into these categories," requiring inspection. On the other hand, he is confident that City Hall's long renovation will prevent any need for major repairs to the city's largest stone structure.

The high-rise owners were well-represented in negotiations. I asked DiCicco if smaller-building owners that barely come under the ordinance raise a stink once they realize they have to hire inspectors just like Liberty Property Trust and other high-rise owners. "I suspect we are going to hear from some people," DiCicco agreed.