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What Is a Roof Cover Board and Why Is It Important?

FiberTite Roof Cover Board
September 14, 2019 at 6:00 a.m.

By FiberTite.

Installing a new roof system is an investment in the protection of a building, business, and people.

It’s your goal to create a commercial roof system with the durability to stand up to mechanical, natural, and human-made wear and tear.

In this 'basic training' article that is ideal for those new to roofing, we will review what a roof cover board is, common types of roof cover boards, and the performance attributes they can bring to the roof system.

What are Commercial Roofing Cover Boards?

Cover boards are thin substrates, which can be made from a variety of materials, that are installed between the insulation and membrane layers on a roof system.

Initially introduced to commercial roof systems to serve as a barrier preventing hot asphalt or solvent-based adhesives from damaging the insulation underneath, roof cover boards were also used to avoid blisters from forming in the system from insulation off-gassing when it came into contact with these adhesives.

Since then, cover boards have been commonly used to add durability to roof systems and have become a widely accepted roof component that adds a variety of attributes to commercial roof design.

Roof cover boards have a variety of uses within a roof system:

  • Creating a suitable substrate for membrane installation

  • Adding durability to the system

  • Improving impact resistance

  • Limiting external fire spread

  • Adding to wind uplift resistance

  • Creating a thermal barrier

  • Creating a vapor barrier

Cover boards can also be used in re-roof applications where the board is installed directly on an existing roof system to provide a suitable substrate for the new roof system.

There are times that a roof system will choose not to have a cover board installed for a few reasons:

  • Cost - you have the cost of the materials and the time/labor to install

  • Low Traffic - the roof system does not have a high amount of foot traffic or the need for high impact resistance

Cover boards are often overlooked during the design of a roof system but selecting the right one may help the system installation and enhance the longevity of your roof system.

Types of Commercial Roofing Cover Board

Commercial roof cover boards come in a wide variety of materials. When choosing the right cover board for your project, you need to consider fire resistance, moisture resistance, wind uplift performance, and system durability.

The various types of cover boards all possess different properties making each better-suited for specific installations than others.

Types of commercial roof cover boards on the market include:

  • Gypsum Fiber – fiber-reinforced gypsum board without a fiberglass mat facer

  • Gypsum – gypsum board with and without a factory laminated fiberglass mat facer

  • Wood Fiber – wood fiber combined with a resin binder, can be asphalt primed

  • Cement – cementitious base with mesh reinforcement

  • High-Density Polyiso – compressed polyisocyanurate with a coated glass-mat facer

  • Perlite – volcanic materials combined with minerals, fibers, and cellulose binders

  • Asphaltic – a mixture of minerals and asphalt with a fiberglass facer

  • Mineral Fiber – compressed rock wool or mineral fiber

  • Plywood/OSB – compressed layers of wood bound with a resin, sometimes with veneer

Read More: Cover Boards for Low-Slope Roofing Systems

How Commercial Roof Cover Boards are Installed

Cover boards can be installed by being mechanically fastened to the structural deck or adhered the underlying substrate. Best practice for installation includes staggering the joints of the cover board in each row and to the joints of the rigid insulation below. This reduces thermal bridging and thermal gaps between layers.

More tips on cover board installation:

  • Follow the manufacturer’s instructions for loosely abutting or gapping the boards during install - this can minimize or eliminate buckling of the cover board as a result of thermal expansion, which can cause unsightly ridges in the surface of the roof.

  • Thoroughly walk the boards in or weight them when adhering the cover board in foam adhesive – this ensures the cover boards form a suitable flat substrate for the membrane.

Commercial Roof Cover Board Performance

According to the National Roofing Contractors Association (NRCA), roof cover boards are critical for functional roof assemblies, with good reason. They enhance a membrane roof system in several ways preventing or minimizing the potential damage that may occur during inclement weather.

Roof Cover Boards Add Durability

Commercial roof cover boards add strength and durability to a roof system to minimize damage from hail, heavy foot traffic, mechanical systems, wind-borne debris, and other threats. This is accomplished by installing the cover board material beneath the membrane and above the insulation foam, providing more stability for the membrane and protection for the underlying insulation.

Read More: Covering Your Options

Roof Cover Boards Act as a Thermal and Fire Barrier

Cover boards have a variety of uses within a roofing system. In addition to their use as a substrate for the membrane, cover boards can also be installed as:

  • A thermal barrier - which is when the cover board is installed directly to the deck to enhance internal fire resistance.

  • A substrate for a vapor barrier – some cover boards have the ability to withstand water

  • A recover application - where the board is installed directly to an existing roof system to provide a suitable substrate for the new roof system.

Insulation can be flammable, so installing a cover board can help deter the spread of fire from outside the building to the insulation and into your building. Cover boards can also be used to enhance interior fire resistance when installed as a thermal barrier.  There are even several types of cover boards that can improve fire code ratings as part of the assembly.

Roof Cover Boards Assist with the Compatibility of Adhesives

Roof cover boards add more than just their performance attributes to a commercial roofing system; they can make installation easier by providing a flat, suitable substrate for the membrane.

When you install a cover board on top of commercial roof insulation or an existing roof system, you provide a stable, smooth surface for the membrane to adhere to. When there are irregularities across the roof substrate surface, the installation of a cover board helps to ensure that those irregularities don’t transfer through to the roof membrane, ensuring a more aesthetically pleasing roof system.

Commercial Roof Cover Board Best Practices

When it comes to commercial roof cover boards, it pays to follow the membrane manufacturer’s recommendations and select a product well suited to the application. This will ensure the most extended life for the membrane roofing system and protect your warranty coverage.

Are you ready to design your next roof system? Contact our team today to ensure that you build the best roof system the first time.

Original article source: FiberTite

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