As we’ve previously covered on the blog, there are five main types of cover board materials, each is best suited to the method of attachment in the roof assembly and the type and method of roof membrane being installed over top, and each with its own benefits. In this week’s article, we’re focusing on the pros and cons of Asphaltic Core Boards and Glass-Faced Gypsum boards to help you make a more informed decision when it comes to your roof health.
Asphaltic Core Board (also known as protection board)
Asphaltic core board is typically fabricated with an asphaltic core sandwiched between glass fibre reinforcement. This method allows for a board that is stable and weather resistant while still being flexible. Asphaltic core board is primarily used with hot-applied asphalt membranes, self-adhered and SBS modified bitumen systems.
- Highly water-resistant:
- Because of the asphaltic core board application process, this cover board is highly resistant to water and is often used in waterproofing applications.
- Excellent puncture resistance:
- Asphaltic core boards are extremely puncture-resistant, and offer high-dimensional stability, making them the ideal choice for roofs that are multi-purpose, regularly trafficked, or have equipment on them that needs to be serviced regularly.
- Not suitable for all membranes:
- Because of the asphalt content, these cover boards are typically not well suited for use under single-ply membranes that may be affected by contact with asphalt.
- Thinner boards are less energy-efficient:
- Asphaltic core boards are low on the spectrum of thermal resistance, and will likely not provide sufficient protection for use over heat-sensitive insulation areas.
- Due to the impermeability of this cover board (which is what allows for its waterproofing properties), there is an increased risk for blistering during the application of the hot asphalt. With this kind of membrane, it’s crucial to work with an experienced professional. Asphaltic core boards are a relatively new cover board option, and according to Roofing Canada, do not yet have national standards. Therefore, when using this product, it is crucial that your contractor understands the ins and outs of its usage.
Glass-Faced Gypsum Board
Exterior Gypsum Board is comprised of a non-combustible, moisture-resistant core wrapped with fiberglass facers on both the front and back surfaces and long edges. According to Gypsum.org, this material has a proven record of cost-efficient performance and fire resistance that has made it a staple material for roofers since the mid-80s.
- No organic materials mean no mould:
- The lack of organic materials in glass-faced gypsum board means that it is highly resistant to moulding or rotting when subjected to moisture. This is a huge advantage in areas where weather cycles routinely, and condensation could cause mould to form over time.
- Classified as a thermal barrier:
- Gypsum boards are non-combustible, which classifies them as thermal barriers. This may be required under certain membrane systems to achieve specific Class A fire resistance ratings.
- Highly Traffic Resistant:
- Gypsum boards have a compressive strength almost twenty times greater than wood fibreboard
- Noise Control:
- Gypsum boards have been used in roofing assemblies where sound reduction was a concern. It effectively helps reduce the transmission of noise in areas where it is present.
- There have been reports of blister formation and frothing of asphalt when hot process roofing systems (BUR and modified bitumen) have been applied over glass-faced gypsum boards. This is something that does not happen with proper application, but unfortunately, without priming the surface of the board, it is much more likely to occur.
No matter what cover board options are presented to you, the most important factor in your roof assembly is working with an experienced contractor who is able to understand the requirements of your space over time and recommend membrane and cover board options that will ensure the health of your roof in five or ten years. If you’re unsure of what the right route is for your roof, contact our experts. With over 60 years of experience, we’re here to help. That’s the Elite Advantage.