ABSTRACT
Of the various thermal insulation boards used in roofing, we recommend a cover board or second layer when glass fiber, polyisocyanurate, extruded polystyrene, and expanded polystyrene insulations are used for the first layer. This concept does not meet with universal approval – many suppliers believe their foam product can go it alone, without a cover board, but they are wrong for the following reasons:
• The denser and stronger cover board armors the membrane against impacts. The more impact resistant the system, the more likely it is to survive both the intentional and unintentional abuses during construction and service. As an example, when built-up roofing systems are exposed to severe hail, the membrane applied on glass fiber insulation will probably be punctured, while the same membrane over cover board and glass fiber insulation will survive.
