In a field in South Florida, thousands of strips of painted metal hang on panels, exposed to sun, rain, extreme heat, high humidity, salt and the occasional hurricane.

They have been hanging there for almost 30 years, just waiting for something to happen.

So far, nothing has happened.

Which is pretty boring if you are a metal panel, but good news if you are the folks at Atofina Chemicals Inc. in King of Prussia, Pa. Atofina manufactures Kynar 500, the polymer resin that is coating those panels, at a plant in Morrisville, Pa.

As is the case with all roofs, metal roofs are under constant attack by time, the elements and pollution. The tendency of metal to corrode unless it is regularly maintained has helped push it to the bottom of the list of residential roofing materials.

According to Robert A. Iezzi of Atofina's research and development division, long-term tests of Kynar have shown no evidence of corrosion.

That's why Kynar-coated metal roofing and aluminum extrusions -- window frames on the Liberty Place skyscraper in Philadelphia, for example -- typically come with a 30-year guarantee.

So far. Those metal panels are still sitting in the South Florida sun, the humid air of Singapore and in the Arizona desert, which means the guarantee may be extended if the test results warrant it.

The reduced maintenance offered by such polyvinylidene fluoride coatings -- Hylar 5000 from Ausimont USA Inc. of Thorofare, Pa. -- has helped put metal roofing back on the list of materials used in residential construction.

Iezzi emphasized that Atofina does not make metal roofing, just the resin that paint companies use to manufacture the coatings.

"The paint then goes to a coil coater, who applies the paint to huge rolls of steel as the rolls are uncoiled," Iezzi said. "The metal roofing is fabricated from the coils."

Manufacturers of metal roofing claim that the coatings prevent fading, chalking and damage by pollutants -- the reasons why those metal panels have shown no sign of aging.

The resins also have expanded the number of available roofing colors.

"We have seen an increase in interest in metal roofing materials on the contractors' side," said Jean Dimeo, the editor of Building Products magazine in Washington.

"The fact that it's easier to install and comes in shake and shingle styles, as well as standing-seam panels, has done much to lower the cost," Dimeo said.

Although ease of installation makes metal roofing a viable alternative for contractors looking to cope with the recent labor crunch, Dimeo pointed out that a metal roof is still three times more expensive than an asphalt one. The average asphalt roof lasts 17 years, but some roofing contractors put its longevity as high as 25 years.

Cost was not a consideration when Better Homes & Gardens magazine used a standing-seam metal roof on its Blueprint 2000 home, which was built in 1999 outside Chapel Hill, N.C.

"It was durability and low-maintenance," said Joan McCloskey, the magazine's building editor. "There was no debate among the designers and staff. We wanted a metal roof."

The house is surrounded by pine trees, and one maintenance advantage, according to McCloskey, is that falling pine needles slip right off the roof.

"With an asphalt roof the needles would be all over the place, clogging the gutters," McCloskey said.

Trees are the reason some houses in the Southwest have metal roofs.

"Around here, metal roofs are required by fire code along the tree lines, wherever there are evergreens," said Deanna Colfer, president of Southwest Builders & Developers in Reno. "Elsewhere, it is a matter of choice."

Most residential builders in Colfer's area use terra cotta roof tiles, which weigh about seven times more than metal roof tiles, according to Atofina's Iezzi.

Metal roofs predominate in Reno's commercial market, Colfer said. "I've got a commercial building in Reno with a cedar-shake roof that I'll be taking off and replacing . . . with metal," she said. "Metal just looks more modern and cleaner."

Dimeo, the Building Products magazine editor, said metal roofing's growth is biggest in New England and the Pacific Northwest.

Still, the Metal Roofing Alliance in Gig Harbor, Wash., acknowledged that metal -- zinc, steel, copper and galvalume (galvanized steel) -- accounts for only 4 percent of roofing used in residential applications, or about 3.5 million houses.

The alliance expects the percentage to double by 2003.

Metal roofing remains popular in places such as Key West, Fla., which was developed about the time that terneplate -- sheet iron or steel coated with a tin-lead alloy -- was widely used in construction. In fact, many veteran roofers still refer to metal as terne.

However, even in areas where metal roofing is popular, it is found on custom houses, not on production homes.

Although reduced maintenance is a modern concept, metal roofing is not. Thomas Jefferson's Monticello, for example, has a metal roof, in keeping with the third president's penchant for novelty and experimentation in architecture and construction.

"Copper and tin, too, were very big in roofing at one time, but we get little call for it these days," said Dennis Dunbar, owner of Dunbar Roofing & Siding in Berwyn, Pa.

"We do a lot of estimates on replacement roofing, and the demand for metal just isn't there," Dunbar said.

According to Dunbar, copper is durable, lasting 35 to 40 years, but oxidation turns it green, which some homeowners don't like.

Most homeowners tell Dunbar they don't want a metal roof because of noise. "A lot of people find the sound of rain beating on a metal roof annoying," he said.

There was, of course, a maintenance issue with terne roofing.

Dunbar said that to prevent corrosion, metal roofing had to be painted every seven or eight years, typically with a red paint known as Tin-O-Lin. The paint is still available at outlets that cater to the roofing trade.

"Seven or eight years doesn't seem all that intense, but a lot of people didn't want to do it," Dunbar said.

That's what the Irish government found in the 1950s and '60s, when, as part of a modernization program, it used heavy financial subsidies to persuade rural inhabitants to shift from slate and thatch to corrugated galvanized metal roofs.

According to Hugh O'Neill, a thatcher from County Galway whom the Irish Office of Public Works employs to repair the roofs of historic houses, this left the country with only 4,000 thatch roofs out of 775,000 public and private buildings.

Recognizing the tourist draw of thatch roofs, and with the countryside dotted with thousands of rusting metal roofs, the government is now paying $4,300 to each homeowner willing to have his roof thatched, O'Neill said.

Still, on the East Coast there are homeowners who want metal roofs on at least part of their houses.

Bob Shirey of Shirey Construction Co. in Wyebrook, Pa., just put a standing-seam metal roof on the 12-by-12-foot porch of a new house in Wyebrook.

The panels, coated with Kynar 500, became easier to install as Shirey and his crew worked. "Once we got the hang of it, it went pretty well -- about five minutes to install each of the 14-foot panels, which are connected by a clip system," Shirey said.

To ensure success, Shirey and his crew simply tailored the rules of installing metal flashing details to the entire roof. "The toughest thing was to make sure that the ribs of the panels didn't end up in the middle of a valley," Shirey said.

He said his next metal roof will be installed on a log cabin.

"A metal roof really looks as if it belongs there," Shirey said.