Roof Coverboards: Cement Board vs. High Density ISO

low slope steel deck illustration

As we’ve covered in this article here, insulation coverboards are a crucial layer of the roof assembly. Made out of different kinds of materials, coverboards allow for a smooth and even application of the roof membrane, and protect what is below said membrane.  Each coverboard material is selected based on the needs of the roof in question, and which membrane will be used overtop. Cement board and High Density ISO coverboards are often used with the same types of membrane, so we’ve broken down the pros and cons of each.

Cement Coverboard: 

Roof section displayed with a cement coverboard


Puncture Resistant 

Cement coverboards are an ideal material for high-traffic roofs because they are extremely puncture resistant and have a high compressive strength.

Fire Resistant

With cement coverboards, water is chemically bonded into the content of the coverboard, and is chemically present. This makes the material highly fireproof. If your building is housing a factory with flammable materials or requires a Class A fire rating, having a fireproof coverboard may be a top priority for your roof.

Easy Application

Cement coverboards can be applied hot or cold, which is a huge asset when odour is a concern. These coverboards can also be applied with adhesive, which means that they require less manpower for installation.


Cement coverboards have been shown to withstand deterioration, warping, and jobsite damage over time compared to other coverboard materials.


The top surface of cement coverboards allows for a wider variety of roofing systems applications, including torch, mop or self-adhered modified bitumen, fully adhered, fluid applied, or metal roofs.


Lower R-Value 

In general, the higher the r-value of a coverboard, the more insulated your building will be. Cement coverboard’s r-value is lower than that of high density ISO based on a comparable thickness of materials.


If roof access is difficult, or if the structure of the roof makes it a challenge to bear the load of the coverboard, your roofing contractor may suggest a lighter option.

High Density ISO: 

Roof section displayed with a high density ISO coverboard.

High-Density ISO performs similarly to cement coverboards with one major difference; weight. The boards are constructed from a rigid, closed-cell polyisocyanurate foam core bonded on both sides to inorganic coated glass fiber facers to provide better resistance to mold growth and stability. The method used creates a lightweight material that is also extremely flexible.



According to Construction Canada, “high –density polyiso coverboards on average weight 66 to 80 percent less than gypsum and cement products with the same thickness.” For certain roofing jobs (such as high rise buildings), this can be an important factor to consider if the roof access is limited and heavier materials can’t be easily transported onto the roof.

High R-Value

A high r-value means that the coverboard has a higher insulating component, increasing the energy efficiency of your building.


Because of their material, these coverboards do not create the same dust that can occur when cutting cement coverboards.

Easier Cutting

Because they are such a lightweight material, this type of coverboard can usually be cut quickly using a utility knife, saving time during your replacement or repair.


More Expensive

High-Density ISO coverboards are more expensive than their cement counterparts however, because they are so much lighter, they may actually save money over the course of your repair or replacement. They are much easier to work with, and are much more easily transported and installed. Before deciding on which material you’d like to use, talk to your contractor and ask about the cost of materials vs. the cost of installation. You may find that the high-density ISO coverboard lowers the overall price of your roofing work.

When trying to figure out which materials will work best for your roof, the best course of action is always to involve your roofing contractor and let them know what functionalities, like fire resistance or puncture resistance, are most important for your structure. Cement and High Density ISO coverboards are both options that will work for most roofing systems, but if you’re curious about what else is out there, we’ve briefly outlined the top five coverboard materials here. If you’re thinking about replacing or repairing your roof and aren’t sure where to start, click here to contact us. We’re here to help make your roof the best it can be for the long haul. That’s the Elite Advantage.