When Hurricane Andrew slammed into the South Florida coast on August 24, 1992, it delivered a stern wake-up call to many in the Metro Dade building industry.

The pounding storm laid waste to CMU buildings, ripped roofs from houses, and turned 2-by-4s and roofing tiles into deadly missiles that smashed through windows and walls. Virtually every type of building construction suffered some degree of damage from the hurricane.

In the weeks and months that followed, disaster teams and building officials sifting through the damage and debris assembled a disquieting tale of how construction deficiencies were responsible for a significant amount of the damage. From inferior construction details to lapses in code compliance, Hurricane Andrew exposed many weaknesses undermining South Florida's building code requirements.

Not long after, South Florida's building code compliance offices instituted a series of new code requirements that sought to fortify the lines of defense for homes and commercial buildings against similar levels of destruction. In hopes of minimizing the damage caused by windblown debris, the code requirements were toughened on two fronts: reduce the amount of flying debris by reinforcing methods of attachment of cladding; and require that building exteriors be able to withstand more severe impacts. In many respects, the resulting code requirements are the most stringent in the country.

With the adoption of the new building codes, many cladding materials, including EIFS -- as well as windows, shutters and siding -- were effectively barred from use in South Florida until they measured up to code requirements. While a casual observer may have thought it unlikely that EIFS would ever meet approval under the stringent requirements, today, however, at least four EIFS manufacturers are making efforts towards approval. Also, one manufacturer has already been approved under the most restrictive code requirement.

Under current South Florida building codes, any cladding system must meet one of three criteria before it can be installed in new construction, according to Candido Font, plan examiner with the Metro Dade Building Code Compliance Office. Those options are:

• If applied over concrete, CMU or 5/8" plywood substrates, it must be demonstrated that the cladding can be anchored to the substrate in such a way that, during extreme negative wind loading, it does not come off the substrate. The test is administered by subjecting claddings to between 1,342 and 9,000 wind cycles.
• If installed at heights above 30 feet over other substrates, claddings must pass a "small missile impact test" which involves the repeated firing of 30 pieces of roofing gravel at 50 miles an hour.
• In all other circumstances, cladding must pass the "large missile impact test", the most extreme of the South Florida requirements. To pass the test, claddings must be able to withstand the impact of a 2-by-4 fired from a cannon at 34 miles an hour.

"In the long run, it will be good for the industry," noted Dave Stender, of W.R. Bonsal, Inc., which expects to get approval in the near future for its standard system applied over CMU and plywood.

"It seems like a very severe test, however I'm sure the industry can get through this," said Mike Irving, director of technical services for Finestone® , which has tested numerous wall assemblies in hopes of obtaining South Florida code approval. "The industry has taken the challenge. It's spent a lot of time, money and research to meet their needs and it speaks well of the industry."

Given the extreme requirements of the test, the initial thinking of cladding manufacturers was that the requirement was too stiff, and that the south Florida market would be closed off to many in the industry, noted Vinu Abraham, general manager of Hurricane Test Laboratory, Inc. in Riviera Beach, Fla.

"However, after two years in the enforcement cycle, we have been inundated with requests from the metal building and EIFS industries with designs they've come up with, which they have asked us to investigate and see if they could perform.

"The large missile test is extremely tough to pass, but it has really heightened the level of innovation and creativity in the marketplace as manufacturers work to meet the requirements of this test," Abraham continued. "We have been impressed with the amount of innovative thinking that this test has provoked."

The large missile test literally puts cladding materials under fire from a compressed air cannon that propels 7- to 9-foot-long 2-by-4s weighing between 9 and 9 1/2 pounds at test panels. The compressed air cannon is similar in many respects to a tennis ball machine. Abraham noted the Navy and Air Force have used similar apparatus for years to test aircraft canopies.

"It's believed to simulate the type of impact load that would occur in a hurricane," explained Abraham. "It applies to windows, doors, storefronts, metal building systems, EIFS and other building systems -- anything that's used on the exterior surface."

The impact test is typically conducted in two locations on the test panel: in the geometric center, and within 6 inches of a corner. More impact locations may be required, based on how complicated the system is. "We will impact as many different locations as necessary to establish any weak links in the system," Abraham said.

As one might expect, a typical Class PB EIFS exterior cladding applied over gypsum sheathing does not hold up well under the large missile test. "We haven't found them to perform well," said Abraham. However, Abraham notes that systems incorporating multiple layers of mesh can pass the test.

For example, the approved Dryvit® system utilizes a layer of Panzer® mesh which is initially embedded in a base coat over the EPS foam. The system is subsequently finished with another layer of standard mesh, base and finish coats. Noted Dick Kroll, manager of engineering services for Dryvit® , the approved system is the very same system the manufacturer offers for high-impact applications.

In a similar fashion, other manufacturers have had success testing systems incorporating multiple layers of mesh. However, the added labor and material costs needed to reinforce the EIFS system may also make it cost prohibitive. Consequently, some manufacturers have focused on obtaining approval for installations over CMU or plywood sheathing as an alternative to meeting the large missile impact requirement.

"There has been a mixed bag of efforts," said Abraham. "There's a certain number of manufacturers that are pursuing the easier of the options, figuring that's at least one way they could tap the market."

According to Tom Remmelle, manager of technical services for STO Finish Systems, the manufacturer was easily able to satisfy the small missile impact test requirement. However, meeting the large missile requirement involves a more concerted effort.

"We've done some evaluations, and we're looking at different reinforcing meshes that eventually will allow us to meet the impact criteria," he said. "Small impact is not a difficult test to pass. Our standard system meets that criteria."

While the large missile test is tough enough, Stender and other manufacturer's representatives noted that the approval process itself is perhaps the most trying aspect of hurricane code requirements. Even when all test requirements have been met, it can take an indefinite amount of time before approval is granted.

"It could be months, years. It's difficult to say," Stender said. "But we have never backed down from code challenges, that's for sure."

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