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Hurricanes and Roofing

The latest update on single plies and hurricanes

Dec 1, 2004
By: Dick Fricklas
Roofing/Siding/Insulation (RSI)

Observations on the recent Florida hurricanes have been collected by a number of credible sources, and reports will be forthcoming for the next several months. However, even the preliminary data on Hurricane Charlie reported by Mark Graham of the National Roofing Contractors Association (NRCA) gives some room for thought and preventative action.

One item reported by Graham was on the performance of fully adhered single-ply membrane systems.

In a number of instances where single-ply membranes were adhered directly to polyisocyanurate insulation, the insulation's topside facers delaminated from the insulation's foam cores.

One problem with faced isoboards has been delamination caused by construction traffic or by hail impact. Apparently cells directly beneath the dynamic load will crush and lose their integrity. The industry has verified this with simulated rolling loads, and has introduced a Rolling Load Emulator Test, which is still under development.

The NRCA has for years recommended that non-foam overlay boards of wood fiber, perlite, glass-fiber or gypsum be used beneath the membrane when hot BUR or modified bitumen is to be applied, for fear that blistering would occur.

However, with single-ply systems, perlite's peel strength is too low to be trusted with the single-ply bonding adhesives, and glass fiber has low compressive and laminar strength, really leaving us with only three choices—wood fiber, gypsum, or the isoboard's facer itself.

According to RSI's 2005 State of the Industry Report, almost 50% of commercial roofing contractors say they install a cover board over polyiso in most applications.

But what shall we do for these adhered single-ply systems in high wind or hail impact areas?

One choice would be to use primed gypsum board overlays, which are generally mechanically fastened through the isoboards into the roof deck. Ironically, these gypsum products have recently been reformulated and improved. Their organic facers have been replaced with glass fiber for improved moisture resistance, and the top surface has been primed.

Another possibility would be to bring back the concept of using nailers to divide the roof into quadrants, or to supplement the adhesives with through-fastened battens, periodically across the field of the roof. That way, should a membrane delamination occur, the peel forces would be confined to the area within the boundaries of the battens.

In a sense, the same layouts already being used for FM Global's mechanically fastened single-ply systems would just be incorporated into these fully adhered systems. We would place the nailers closer together in the high uplift force areas—corners and perimeters—much as we do with half-sheets in mechanically fastened systems today. The nailers would be spaced at greater distances as we move toward the field of the roof, away from the higher wind coefficients.

Since fully adhered systems are highly desirable in high wind areas, (ballast may become airborne missiles, and mechanically fastened systems are subject to flutter, fatigue and fastener back-out), the batten system seems to provide a fail-safe mechanism.

In Florida, Graham and other observers implicated inadequate edge attachment. The ANSI/SPRI/ES-1 provisions, when followed, did very well in the Florida storms. The ES-1 document is part of the Florida Building Code, the International Building Code, and the NFPA 5000 Code. Graham also noted a dramatic difference in performance between the continuously cleated edge metal systems and those that were uncleated or only partially cleated.

How can I find out more information?

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