With the rising popularity of metal roofs and insulated roof decks to improve energy efficiency, it has never been more important to safeguard the thermal stability of a roof. A key element to achieving this is through finding the right roof underlayment designed for the job. While most roofing underlayments perform admirably in normal rooftop conditions, there are some circumstances where a roofing underlayment needs to meet a higher in-service temperature:
Darker colored roofs
Roofs in climates like the southeast U.S. where there’s longer sun exposure
Roofs in high altitude regions where the UV rays are stronger
The configuration of the roof assembly and the placement of insulation in the assembly will also play a factor in determining the in-service temperature. For example, if the building has a vented roof with insulation directly on top of the ceiling, air can come into the structure at the eaves and vent out at the ridge of the roof. This airflow helps the underlayment remain cooler due to the intake and exhaust of air.
Using unvented assemblies with insulation that is directly in contact with the roof deck creates a high amount of stress on the roofing underlayment because the heat essentially has nowhere to go. This drives up the surface temperature of the roof. It is important to avoid letting the roof become too hot, as the self-adhered roofing underlayment may soften and drip into gaps in the roof sheathing or plywood and get into the building itself.
In most cases where there is a vented roofing assembly, a standard roofing underlayment will have sufficient heat resistance to prevent this. However, if the roofing design is likely to result in a more extreme in-service temperature, it’s safer to switch to a roofing underlayment designed for high temperature.
In these cases, the roofing adhesive has been modified to perform in high heat, without softening. These high temperature (HT) products are generally designed to perform up to 240° F. There are also certain situations, (such as with copper or zinc roofs with unvented roof assemblies), that call for roofing underlayments with butyl adhesive, which are designed to perform up to 300°F.
Help homeowners select the proper roofing underlayment by using tools like tools like WUFI® hygrothermal modeling to help them assess the likely in-service roof temperature. In addition, teach them about the temperature performance window of the various underlayment products so they can make the best choice to protect the roofing assembly and ensure it performs well for the long run.
Original article source: GCP Applied Technologies