Summary of Common Defects with Foamed Adhesive Application and Rigid Insulation Installation (as Previously Reported)

The use of foamed adhesives (defined in ASTM D907-08b [2] as adhesives with an apparent density that has been decreased by the presence of numerous gas – filled cells throughout the mass) is an established method for adhering roofing assembly components, including faced rigid cellular polyisocyanurate thermal insulation board as defined in ASTM C1289-10 [3] (insulation board), to the roof substrate and to each other within roofing assemblies. The proper design and installation of insulation board roofing assemblies are critical to the success of systems that rely on attachment with foamed adhesive. The detachment of insulation in service often contributes to roofing assembly failure, and defects related to roofing assembly design and insulation installation are often the root failure mechanism. Detached or poorly secured roofing assemblies cannot resist significant wind loads and are likely to be further damaged or destroyed by wind events well below the design wind pressures for the assembly.

Our recent investigations of failures of roofing assemblies that include foamed adhesive have revealed several distinct adhesion defects. These defects are independent of the type of roofing membrane and can be attributed to the application of the foamed adhesive, as well as to the placement of the insulation boards into the adhesive. These four distinct and common defects are improper foamed adhesive spacing and pattern, insufficient foamed adhesive quantity, inadequate insulation board to adhesive contact, and failure to maintain insula­tion board contact with the substrate. All of these defects reduce the uplift re­sistance of the roofing assembly and increase the likelihood of roofing detachment. In cases of partial failure in which the center of the roofing assem­bly becomes detached but the roofing assembly remains attached at the roof pe­rimeter, these defects allow insulation movement and displacement, which can render the roofing assembly unserviceable.

Copyright by ASTM Int’l (all rights reserved); Tue May 6 12:07:08 EDT 2014

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Case Studies of Roofing Failures due to Moisture in Roofing Assemblies