Why Your Underlayment Matters

By Cass Jacoby, RCS Reporter.  

Underlayments are key to a high-performance roof. 

When it comes to a roofing system's resistance to fire, rain, snow, ice and high winds, underlayments play a critical role. An underlayment lies between the shingles and the roof sheathing or roof deck, providing a secondary layer of protection against the elements.  

In a recent article shared by UL, a non-profit global leader in the science of safety, the importance of underlayments is discussed along with considerations for their performance in roofing systems.  

Technical Director, Built Environment and Corporate Fellow - William Henry Merrill Society Dwayne Sloane writes, “[UL’s] experience and distinct testing over many years clearly demonstrates the importance roofing underlayment plays in the overall roof assemblies.”  

Building codes are determined by the International Building Code (IBC) and the International Residential Code (IRC) and require certain testing and specifications for underlayments so that roofing materials are properly installed with their intended use. 

Fire performance 

Not all homeowners realize the importance of the fire test, as hail or wind is often thought to be more important. There is a misconception that fire classification rating is only based on the roof covering (asphalt glass mat, metal, concrete, clay, etc.), however, underlayments play a crucial role in fire classification. Thus, underlayment is the deciding factor of how certain roof coverings can achieve the desired fire classification.  

During Standard Test Methods for Fire Tests of Roof Coverings, a burning brand test is conducted. In this test, heat is transferred directly through the roof covering to the roofing underlayment, which is why the underlayment plays a significant role in the overall system's fire rating. Consequently, many certifications of roof covering materials describe specific roof underlayments the test was conducted with. With a compatible roof covering and underlayment combination comes a peace of mind that your roofing materials are working together for top performance.  

Wind and impact resistance performance 

Roofing products and systems are also required to be tested and evaluated for wind and impact resistance. Some tests factor in underlayments while others don’t, so be sure to talk to your contractor about this and see if underlayments type is a factor in wind and impact resistance. 

Conclusion 

In addition to roofing systems' performance concerns, there are several other considerations of physical properties for underlayments products. These characteristics evaluate the overall performance of underlayments, they include product mass, breaking strength, pliability water transmission, perfect ash, tear, flexibility and more.  

It is essential to identify on the underlayment packaging that these products comply with the specification. One way to check this is by way of the UL Certification Mark on the product. UL Certified underlayment products tested and certified to any of these specifications are identified by a UL Certification Mark on the roll, package or container. This provides confidence that the underlayment complies with the code requirements. 

In conclusion, it is essential that the underlayment evaluated as part of the roof covering be certified, labeled and used appropriately in the field application. 

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