This March, Miami-Dade building authorities took the unusual step of revoking county-wide approvals for many brands of galvanized roofing nails. The reason? Research by University of Florida experts demonstrated that some nails suffered corrosion in industry standard tests. Specifically, the nails that were treated by electroplating rather than by mechanical galvanizing or hot-dip galvanizing were observed to have suffered rapid deterioration. That's a claim long made by suppliers of hot-dipped and tumble-galvanized fasteners, who have been saying for decades that their product is better. The University of Florida research appears to bear that claim out (see PowerPoint PDF: "Corrosion of Roofing Fastener Systems," by Kurtis Gurley and Forrest Masters).

To learn more, JLC spoke with University of Florida professor Kurt Gurley. Gurley was quick to point out that research is still ongoing, and that his team's report made no recommendation about product approvals. Miami-Dade officials acted on their own, said Gurley. Also, Miami-Dade is just a single county in a single state; the county's action will have no direct effect on building department policies in the rest of the 50 states, or on the other counties in Florida.

But the University of Florida testing has produced troubling evidence that despite being labeled as complying with ASTM standards for thickness of zinc coating, electroplated galvanized roofing nails actually don't pass a common industry standard test for corrosion resistance — which raises the concern that the nails may rust quickly in service, at least under some conditions.

The idea for the testing program originated in the roofing industry, Gurley told JLC, when Mark Zehnal, the Director of Technical Services at Florida Roofing, Sheet Metal & Air Conditioning Contractors Association (FRSA), raised the topic at a meeting of a Technical Advisory Committee for the Florida Building Commission. Zehnal told committee members that his association's members had questions about nail corrosion based on their experience in the field. So the Florida Building Commission tasked the University of Florida team to look into the matter.

Phase One of the investigation was just a survey of professional roofers, to find out whether contractors in the trade would report seeing corrosion on nails in the field. The results of that survey, says Gurley, indicated that a closer look was worth the effort. So in the next fiscal year, the researchers implemented Phase Two: they purchased a random sample of roofing nails from building materials retailers in the field and put the nails through standard corrosion tests. All of the sampled nails were labeled as passing the ASTM standard, but in the University of Florida testing, all of the electrogalvanized nails corroded badly. Only the hot-dipped galvanized and mechanically galvanized fasteners passed the tests.

Dade County has its own, tougher standard for galvanized nails. Some of the electrogalvanized nails tested in the University of Florida testing were labeled as meeting that standard; but those nails also failed in the University of Florida test program.

For now, Dade County has temporarily suspended its approval of all the electrogalvanized roofing nails listed with the county (although one manufacturer has reportedly re-qualified its product with Dade County). The Florida Building Commission has not taken any action so far. Meanwhile, Kurt Gurley says, his team's research is continuing, with more fasteners scheduled to be sampled and tested. Said Gurley, "We are slowly building up a portfolio of information with which the stakeholders can make decisions as to what to do."