Utilizing roofing coverboards enhances building resilience

by Katie Daniel | July 13, 2017 2:21 pm

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by Derrick Hutchinson
When it comes to building resilience, the roofing coverboard is often an unsung hero. When installed as part of a properly specified and installed roofing system, this material helps prevent damage to roofs and greatly increase durability. However, very few architects and specifiers consider using these materials on their projects. This is a missed opportunity for both designers and building owners.

The purpose of roofing coverboards is simple—prevent damage from external forces and maximize building resilience. For example, a roof membrane may suffer punctures caused by hail, debris, or foot traffic. This may lead to leaks that spread across the roof and eventually cause internal damage. Even if the membrane stays intact, the insulation can puncture and lose a portion of its R-value. This leads to increased heating and cooling costs for building owners. Roofing coverboards are designed to protect membranes against this kind of damage.

Besides protecting the roofing membrane from direct impact, coverboards have many other benefits making them critical to any project. For instance, they enhance the structure in the event of wind uplift and fire. These added benefits have been proven in certified evaluations of roofs that have experienced extremely harsh weather.

Roofing coverboards also greatly improve the acoustics of a structure, making buildings more inhabitable and comfortable to occupy. When each of these benefits is looked at more closely, the value  of roofing coverboards starts to become clearer.

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Protecting against wind uplift
Wind uplift is the result of negative pressure on a roof caused by wind passing across it. The wind can also cause positive pressure on the interior side of the roof if there is an opening—such as an open or broken window or door—allowing wind to enter the building and build up pressure on the roof underside. The negative pressure created on the exterior of the roof, especially at edges and corners, causes a suction that can pull up elements securing it. The consequences of wind uplift varies depending on the type and age of the structure. The roof can be damaged, or it could be destroyed (possibly along with the building) if the roof is not equipped to handle high wind uplift.

In the event of a windstorm, such as a hurricane, a coverboard adds additional strength, which allows the building to withstand higher wind loads than a roof without one. High flexural strength is one quality that ensures a coverboard can do this. The bond of the membrane to the coverboard also plays a large part in withstanding a windstorm. The higher the peel resistance of the membrane from the coverboard, the better its chances are against high winds. Peel resistance, combined with a higher flexural strength, ensures the coverboard is well-suited for all locations, especially high-wind-zone regions.

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Coverboards as fire barriers
Roofing coverboards help prevent the spread of external fires. For instance, if a tree or adjacent building is ablaze, an ignited branch could land on the roof and burn through the membrane to ignite the insulation. However, the gypsum in roofing coverboard acts as a fire barrier and prevents the insulation below from catching fire.

Gypsum coverboard provides fire protection because of the natural insulating properties of gypsum rock composition. This material contains chemically combined water, which is slowly released once it is introduced to high temperatures. Should a fire occur, the gypsum would prevent the flames from spreading or slow the rate at which it moves to other components of the roof.

To protect against external fires, a Class A rating is ideal. This is evaluated under ASTM E108/Underwriters Laboratories (UL) 790, Standard Test Methods for Fire Tests of Roofcoverings, which requires a roofing system successfully pass an intermittent flame, burning brand, and spread of flame test at a given slope. Having a Class A rating is important for any roof, as roof membranes and insulation easily ignite. Excluding a coverboard from a roof greatly increases the probability of losing the entire structure to fire.

Coverboard also helps reduce or prevent the spread of a fire by acting as a thermal barrier placed directly above the roof deck. In the event of a fire inside the building, it reduces the transfer of heat to the insulation. This slows the rate at which the insulation melts—a process that, if not checked, can cause the internal fire to spread and grow larger.

The thermal barrier rating is an hourly rating determined by a roof-ceiling test method under UL 263, Standard for Fire Tests of Building Construction and Materials, and ASTM E-119, Standard Test Methods for Fire Tests of Building Construction and Materials. These designs are expressed as P-Series, and the evaluation consists of the full roof and ceiling assemblies.

Coverboards enhance acoustics
Imagine working throughout the day and feeling constantly interrupted by the sound of airplanes flying overhead, a heavy downpour, or even someone walking on the roof for a regular inspection. Daily sounds such as these can cause significant disturbance inside a building, and may inhibit someone from completely focusing on their job. Including a coverboard in the roofing system adds a dense layer of material to the roof, which increases its overall ability to dampen noise, preventing sound from entering the building.

One code-designated acoustical rating is sound transmission class (STC). The higher this rating, the less sound passes through a material. Some building codes dictate an STC rating of 50, but this can increase if the building is a school or near an airport.

Not using a coverboard will exclude this layer of sound dampening. As a result, additional layers of insulation or an acoustically rated ceiling will need to be added to achieve the necessary STC ratings.

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Best practices for installation
Installing a coverboard that works with a roofing system is the easiest way to increase energy savings and protect the roof from damage caused by maintenance, weather, or other natural elements. Coverboards can be completely adhered or fastened to the existing substrate, and should be set over the topmost insulation layer. When properly installed, adding a coverboard between the membrane and insulation introduces another layer, minimizing risk of damage to a roof system.

When installing a coverboard, it is important to ensure the roof is free of any moisture, as it is imperative for the roof insulation to be kept completely dry at all times. With this in mind, it is best to avoid installing coverboards during times of inclement weather, including rain. Any moisture leaking into a roof assembly not only damages the insulation and coverboard, but it could also damage the entire roof by decreasing the R-value, rusting the mechanical fasteners and/or deck, delaminating the membrane, and ultimately voiding the roof warranty.

The edge joints of the coverboard should also be staggered in adjacent lengths or offset from layer to layer in relation to the insulation, as this will help to avoid vapor movement and decrease thermal bridging. It is best to only select and install fasteners or adhesives in strict compliance with the roof system manufacturer’s installation recommendations, because some non-compliant options could adversely impact the roof. Proper fastener spacing is also crucial to achieving wind-uplift performance by aiding the coverboard in providing a strong, high-performing layer of protection.

Before proceeding with installation, it is always important to take into consideration and refer to the manufacturer’s written instructions. Design/construction professionals should also be sure to review any local code requirements to ensure proper installation and design. Further, one should seek out building materials put through rigorous testing to verify the intended performance. For example, Factory Mutual Global (FMG) and UL are two world-renowned product testing services trusted by contractors, builders, and manufacturers. Materials certified and approved by third-party testing agencies reveal whether the industrial or commercial product will grant the highest level of safety and resilience.

Taking these steps to ensure proper installation will help reduce risk of loss or damage due to fire, weather, or equipment failure, and drive the long-term success of a roof system.

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Improving a building with coverboards
It is clear coverboards provide many benefits when included in a roofing system, and there are a variety of boards available to meet project needs. High-performance coverboards—gypsum-fiber, glass-mat, gypsum, and cement—typically perform much better than others. They are strong, have higher fire properties, and are dimensionally stable. Knowing which coverboard is right for a project is important, because they all have different benefits.

Gypsum-fiber coverboards
These coverboards are homogeneous gypsum-fiber panels with no facer on the face or back. They are high-strength, fire- and impact-resistant, and perform well in high-wind zones. These boards provide exceptional bond and low absorption in adhered systems, and offer sustainable design for all types of roofing systems, including single-ply, fluid-applied, built-up (BUR), sprayed polyurethane foam (SPF), metal, and modified bitumen (mod-bit) roofing. As a result, they can help contribute toward a project becoming accredited under the Leadership in Energy and Environmental Design (LEED) program.

Glass-mat gypsum coverboards
These coverboards are made of a gypsum core with a glass-mat facer on both the face and back of the board, and have high strength and fire resistance. The strength comes from the glass facer and fire resistance is a natural property of gypsum. Additionally, these boards have high moisture and mold resistance. They work well in all roofing systems, including single-ply, fluid-applied, SPF, metal, and modified bitumen.

Cement coverboards
These typically contain a cement-aggregate core and a glass scrim for strength. They are high-strength, fire- and impact-resistant coverboards that perform well in environments with high humidity.

High-density insulation coverboards
Containing a high-density polyisocyanurate (polyiso) core and a glass facer on the face and back, these are lightweight coverboards with added R-value. They work well in all roofing systems.

Each of the coverboards mentioned in this article has inherent strengths, and each is ideal for different projects. The project type, environment, and immediate surrounding area are three factors that should be considered when selecting a coverboard. Making the appropriate decision increases the building’s longevity immensely.

Architects and specifiers should take steps to thoroughly research the different types of coverboards to learn which can be applicable in their next projects. If adding a coverboard to a building is the difference between its destruction and its resilience, the benefits outweigh the costs.

Derrick Hutchinson is a product manager for USG Roofing Solutions. He has more than 10 years of experience in building product development and system evaluations. Hutchinson is a member of National Roofing Contractors Association (NRCA), RCI, Single-ply Roofing Institute (SPRI), Asphalt Roofing Manufacturers Association (ARMA), and ASTM. He graduated from the University of Illinois at Chicago with a degree in physics, and prior to taking on the product manager role, was a senior researcher at USG’s Corporate Innovation Center. Hutchinson can be reached via e-mail at dhutchinson@usg.com[6].

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