Cover Boards: The Membrane and Insulation Protector

Continuing on our roof system component analysis—after discussion of the roof deck, substrate board, vapor retarders and insulation—we now have worked our way up to the cover board. For the purpose of this discussion, the cover board is defined as the board placed upon the insulation as the final substrate to which the roof cover will be placed.

The purpose of the cover board is multifaceted; it can include:

    Insulation Protection: Placed to protect the thermal layer from the often deleterious effects of repeated foot traffic, which can result in insulation crushing, loss of roof-cover adhesive, inability to resist wind uplift and mechanical- fastener puncture through the membrane.

    Asphaltic core boards are very flexible and will conform to irregular surfaces and offsets without fracture. Here crews work to install the cover board in bead-foam adhesive in preparation for the three-ply modified bitumen roof cover. PHOTO: Clark Roofing

    Asphaltic core boards are very flexible and will conform to irregular
    surfaces and offsets without fracture. Here crews work to install the cover board in bead-foam adhesive in preparation for the three-ply modified bitumen roof cover. PHOTO: Clark Roofing

    Enhanced Roof-cover Adhesion: Cover boards can enhance the bond between the roof cover to the substrate.

    Enhanced Resistance to Wind Uplift: Cover boards and their ability to enhance the bond of the roof cover to the underlying substrate can result in an increased wind-uplift rating above and beyond that which can be provided with organic-faced insulations. They reduce the possible effects of facer-sheet delamination.

    Enhanced Fire Resistance: Many cover boards will enhance the fire resistance of the assembly.

    Hail Protection: Numerous studies show the value of cover boards in enhancing a roof cover’s ability to resist damage by hail.

    Provides Separation: A cover board provides separation between a roof cover and insulation that may not be compatible or the attachment adhesive of the roof membrane is not compatible with the insulation.

    Reduces Thermal Shorts (Energy Loss): Thermal insulation is often attached to the roof deck with mechanical fasteners, which results in conductive heat loss, up to 7 percent according to the Rosemont, Ill.-based National Roofing Contractors Association. This is a large value when some roof covers, which utilize mechanical attachment, purport to provide energy savings. Furthermore, when only one layer of insulation is used (a cardinal sin in my opinion) an additional 7 to 8 percent energy loss can occur. Placing a cover board above mechanically attached insulation and/or a single layer of insulation will enhance the energy performance of the roof system.

    Enhanced Roof-system Performance: I firmly believe the use of a roof cover board in a roof system improves the overall performance of the roof system and increases the probability of the roof attaining a long-term service life, which is the essence of sustainability. NRCA agrees; the organization recommends the use of cover boards in all low-slope assemblies.

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