Insulation cover boards are an essential layer of the roof assembly. Overlay boards made of a material, usually under 0.5” thick, that is formed into panels 4 feet x 2, 4 or 8 feet in size and sandwiched over top of the base layer of thermal roof insulation and underneath the roof membrane. Traditionally, cover boards were made out of wood fiber, but recent innovations have introduced a wide array of materials into the market to suit the needs of different membranes and structures. As a general rule, almost all roofs benefit from the use of a cover board, which adds energy-efficiency and protection to your membrane. There are, however, many things to take into consideration regarding your cover board, how to maintain it, and the rare case where it may actually be detrimental to your roof.

What Does A Cover Board Do?

The main job of a cover board is to provide a smooth and even surface for the application of the roof membrane and protect the inner workings of your roof. According to Roofing Contractor, “studies have indicated that warping of insulation is reduced in double-layered applications because proper adhesion between insulation boards is easier to achieve than it is between the insulation and substrate.” In other words, having a cover board installed makes it less likely that you will have issues with warping and degeneration before the life expectancy of your roof runs out. The staggering of joints between the base layer of insulation and the cover board can also reduce thermal bridging and improve the longevity of your roof membrane.

How A Cover Board Protects Your Roof
Since the year 2000, the NRCA has recommended the use of cover boards. According to Architecture and Construction, “Cover boards minimize damage to insulation caused by foot traffic (service) and/or damage caused during the construction of the roof system (power carts, use of the roof as a work platform, etc.).” In fact, cover board installation has become a requirement for many warranties. The added protection that a cover board gives, along with its ability to protect from damage and fire, are some of the main reasons we recommend it for your roof.  Cover boards are particularly important when dealing with single-ply roof assemblies, as they add a layer of protection that is critical for the membrane, and also may be mandatory for the roof warranty.

Different Cover Board Materials 
Although the benefits of cover boards are vast, it is important to note that a critical component of those benefits is making sure that the cover board your contractor is choosing makes sense with the other materials present in your roof. There are many different methods of attachment that are used for the cover boards, depending on the membrane that is going on top, as well as the material used for the cover board. This is why there are so many different options for materials. Some cover boards are mechanically fastened, while others are attached with asphalt or adhesive.  When looking at the different options, your contractor should consider how each material functions in conjunction with the membrane to produce the best possible result.  There are five main materials that we use for our cover boards, each with their own specifications and use cases: 

Pictured: Dens Deck insulation cover board

1. Perlite Roof Board 
Perilite is one of the oldest cover board materials on the market. According to Roofing Canada, perlite roofing insulation has been used in the US since the early 1950s. The material is fire-resistant, water-resistant, and a more eco-friendly option. According to the CRCA, perlite uses up to 40% of recycled materials. Perlite board is usually used in conjunction with built-up asphalt and gravel as well as 2 ply modified bitumen roof assemblies.

2. Fibre Cement Board
Fibre cement boards are a new material that is showing great promise when used under built-up and modified bitumen membranes. The material has a high moisture resistance and a high structural strength, which could provide a solution for building occupants where moisture is a serious concern.  It is also very rigid and protects the softer thermal insulation below from damage due to direct impact. 

3. Dens-Deck Cover Board
Dens-Deck cover boards provide a suitable substrate for most conventional low-sloping roof membranes. The material is made of a non-structural glass mat applied over a silicone-treated gypsum core panel, and is a great option if your roof is high-traffic. It is one of the most impact and puncture resistant insulation materials offered for insulation on the market today. 

4. Asphaltic Core Board
Asphaltic core cover boards are fabricated with an asphaltic core that is placed between glass fibre reinforcement. This option is extremely moisture resistant, which may make it a good fit for buildings where condensation or positive drainage has been an ongoing concern.  It is most often used with two ply modified bitumen roof assemblies.

5. Mineral Fibre Board 
According to Roofing Contractor,  “The advantage of fiberboard insulation is that it performs well when it is mechanically fastened to the deck. This is an important characteristic when considering the large number of metal decks in use today that require mechanical attachment of insulation.” Mineral fibreboards do not perform well, however, when moisture is involved. 

Risks Associated With Cover Board Installation
If there is a high probability of interior and exterior humidity, it is possible that condensation could form between the layers of insulation, causing damage and deterioration of materials over time. This really only happens in rare cases where excessive heat is being conducted within the structure and is contrasted by low temperatures outside. Several examples of this could be buildings with indoor pools, hockey rinks, or refrigerated storage warehouses [where the freezer area is exposed to the deck substrate]. 

When it comes to deciding on the right material combinations for your roof, it can be difficult to figure out what is worth investing in and what should be left out. Cover boards are a fantastic, and also often necessary, option for maintaining the health of your roof if they are done correctly. When considering this kind of addition to your roof construction or repair, make sure to consult an expert. If you have questions about your roof or are looking for more information regarding cover boards or membrane types, get in touch with us, we’re here to help.