Low-Slope Commercial Roofing

Roof Cover Boards Provide Outstanding Performance
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Robert C. Grupe, CSI, Director, Architectural and Technical Solutions, USG C

Recent Cover Board Developments

In the 1990s, FM Global expanded the uplift ratings of approved roofing systems to include enhanced ratings well above the 90 psf threshold typical before that time.

Furthermore, the protocol for testing these systems was changed from the conventional 5- by 9-foot test table to a much larger 12- by 24-foot table. The larger table minimizes the contribution of the perimeter frame to the tested assembly performance and makes passing at higher pressure levels more difficult. Hence, minor components within the roof assembly, such as mechanical fasteners and cover boards, came to play a key role in advancing the performance of roof assemblies.

Besides increased fastener densities to improve uplift performance, engineering of newer fasteners and the use of more types of cover boards created a wide variety of enhanced wind uplift systems available to the market.

The lessons of Hurricanes Hugo and Andrew that devastated the Carolina and South Florida coasts have led to more frequent specification of enhanced systems. In the case of South Florida, these enhanced systems became a requirement under the new South Florida Building Code.

Code changes have led to the current published inventory of enhanced high-wind uplift systems, which are supported by credible third-party testing. Cover boards have become a critical component in these assemblies, and quantifiable advantages of one cover board over another have been established. Cover board manufacturers invested significant money in testing to prove the threshold capabilities of their boards. Assemblies incorporating thinner boards, fewer fasteners and less adhesive were tested to maximize performance and minimize costs.

Increased use of cover boards over extended periods of time has revealed problems with some cover boards that are sensitive to moisture degradation. In some cases, minor leaks from the exterior and rising vapor from the interior would condense at the roof membrane (with a relatively low permeability) and wet the cover board materials. Rot, collapse and general deterioration of the cover board would follow, requiring the removal and replacement of the roof membrane, cover board and, in some cases, the underlying insulation.

 

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Originally published in Architectural Record.
Originally published in September 2005

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