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.