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The 2004 hurricane season in Florida provided a unique opportunity to observe the performance of spray polyurethane foam (SPF) roofing systems following actual high wind events.

The four hurricanes that came ashore that year demonstrated that SPF roofs performed well. Most SPF roofs survived undamaged or with minor surface damage, and building occupants remained protected.

Some roofing failures were noted, however, due, in part, to the failure of the structural roof deck or the substrate.

Based on small-scale wind uplift testing, SPF roofing systems have achieved some of the highest wind uplift ratings in the roofing industry today. Because of the adhesive, compressive and tensile strengths of SPF, the typical mode of failure in small scale testing (typically 12 x 24 feet panels) is the fastening of the deck (i.e., screw pull-out). Testing over recover panels has suggested that the added stiffness of the SPF roof increases uplift resistance.

Four hurricanes struck Florida in 2004: Charley (August 14, Category 4), Frances (September 5, Category 2), Ivan (September 16, Category 3), and Jeanne (September 26, Category 3). All but Ivan made landfall in areas where large numbers of SPF roofs were present. Inspections of these roofs indicated that, in general, SPF fared exceptionally well. However, some SPF roofs experienced deck failure, substrate failure and surface damage.

Hurricanes are categorized as 1 to 5 according to wind speed using the Saffir-Simpson scale. However, the hurricane category does not accurately reflect the damage potential of the storm.

For example, the wind pressure differential increases as the square of the wind speed. Additionally, the potential damage ratio increases even more dramatically with wind speed than does the pressure differential.

Thus, in comparing a Category 4 storm (Charley) with a Category 2 storm (Frances), the wind speed might be 40 % greater; the pressure ratio would be approximately 100% greater; and the potential damage would be 25 times greater.

Hurricane Charley made landfall on August 13 near Punta Gorda. There were a number of SPF roofs in this area, and it afforded an excellent opportunity to assess damage.

Hurricane Ivan made landfall near Pensacola, but there were few SPF roofs in the region. Hurricanes Frances and Jeanne made landfalls in the same area near Stewart. These two hurricanes provided an opportunity to assess the effectiveness of SPF repairs installed between the two storms.

Deck failure
Roof decks are commonly constructed of concrete, steel or plywood. Decks provide the structural support for the waterproofing and insulating components of the roofing system. Deck failure results from high pressure differentials.

When wind encounters an obstruction, such as a building, air pressure tends to increase on the windward side relative to the leeward side. As wind passes over a roof, the velocity increases because the air must travel a greater distance; as air velocity increases, its pressure tends to decrease (similar to air passing over an aircraft wing). Thus, air pressure on the top of the roof tends to be lower than the under side.

Exacerbating this effect, if a window or door suddenly fails, the pressure within the building can suddenly and catastrophically spike, blowing off portions of the roof deck which might have otherwise withstood the wind loads. Roof deck failures remove portions of the roofing membrane and insulation and expose building interiors to rain and wind damage.