Cover Boards Can Protect Roof Insulation and Prevent Blistering in Low-Slope Roof Systems

Cover Boards

Thirty-five years ago when incidences of degassing and vapor release between polyisocyanurate roof insulation and hot-applied built-up roofing materials began to cause widespread blistering in low-slope roof systems, NRCA issued a bulletin advising roofing contractors to install wood fiberglass board, perlitic board or glass fiber board insulation between the polyisocyanurate roof insulation and built-up roofing to stop blistering. In the years since, cover boards have become a standard method to enhance overall roof system performance for all low-slope roof systems.

Cover boards are available in a variety of sizes and materials. A history of their evolution to become the roofing industry’s solution to roof membrane blistering and provide protection for low-density roof insulation was featured in “Covering your options,” an article in the May issue of NRCA’s trade magazine, Professional Roofing.

Common cover board types used with low-slope roof systems include:

  • Wood fiberboard
  • Perlite
  • Glass-mat-faced gypsum
  • Fiber-reinforced gypsum
  • Mineral fiber
  • High-density polyisocyanurate
  • Cement
  • Asphalt core

“The article helps roofing contractors and roof system designers select an appropriate cover board for a specific situation,” says Jason Wilen, AIA, CDT, RRO, author of “Covering your options” and an NRCA director of technical services.

It is important to review a roof membrane manufacturer’s literature or consult with its technical staff before selecting a cover board. In addition, many roof membrane manufacturers’ extended warranty terms require the use of cover boards beneath low-slope roof membranes.

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