Commercial flat roofs are complex designs featuring up to a dozen layers of different materials, usually beginning with a layer of insulation that is either rigid or spray foam. While these foam insulation layers work wonders for managing heat loss or gain through the roof to control heating and cooling costs, they're also at risk for being damaged either during roof membrane insulation or during later maintenance. Find out how cover boards have been protecting commercial roof insulation layers since the 1970s.
Cover Board Definitions
As the name suggests, cover boards are pieces of material used to cover various layers in a commercial roofing system. These boards vary in size and composition, but they all serve similar purposes in protecting the roof membrane layers from damaging each other. Some of the most popular materials for cover boards include:
- Fibers of glass, minerals, or wood
- Asphalt sheets with outer layers of fiber or mineral board
- Gypsum reinforced with glass.
The first generations of cover boards were simple sheets of these materials, but modern variations include enclosed foam and other advancements that help these boards offer multiple features at once.
In the late 70s, the National Roofing Contractors Association (NRCA) began recommending that installers protect layers of polyurethane insulation foam with cover boards before installing a built-up roof membrane involving hot bitumen applications, which was the primary commercial roofing technique at the time. The hot sealant was causing a gas reaction in the foam that resulted in a blistered, sunk-in, or otherwise damaged finished roof. Damaged foam doesn't insulate as well and puts the membrane at extra risk for tearing. A layer of fiber board or properly treated gypsum kept the heat away from the foam and trapped any gasses that did form so they couldn't rise up and bubble under the membrane.
While these cover boards were first used in built-up applications only, in the following decades the NRCA expanded their recommendations to include almost every type of flat roofing membrane system used commercially. Aside from being used to protect insulation in most new commercial roofing, cover boards are also used today for
- Protecting old roofing membranes from potential chemical reactions when a new and different material is applied during re-roofing
- Underlayment for securely supporting layers of fire or moisture barriers
- Thermal barriers when commercial flat roof is being installed over a metal deck
- Replacing vapor barriers that are tricky to apply in a multi-layered roof system.
It's the useful secondary characteristics of today's advanced cover boards that make them such versatile additions to your commercial roofing project. Basic wood fiber boards just provided stiffness and a barrier to prevent gas transfer, but a modern gypsum board with a foam core doubles as another layer of insulation that isn't so easily crushed by the workers installing the roof membrane. Most modern cover boards also add fire resistance to the roof, which is essential for most commercial building projects where local and national codes are strict on how fire is managed within a large structure. You may be able to eliminate a few layers out of a typical commercial roofing system and save money by choosing a cover board that handles vapor blocking, part of the insulation load, and some of the fire barrier requirement all at once.
Finally, don't forget that cover boards only work for any of these purposes if they're installed correctly. The boards must be overlapped and applied in two layers with the joints staggered. This means that gas that escapes up through the first layer doesn't have an immediate and easy gap to flow through to the membrane layer above. A double application with staggered joints also prevents flexing when weight is placed on the cover board layer.
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