With millions of square feet installed and 50 years of proven performance, PVC and PVC KEE HP roofing membranes have earned the confidence of the design community and a prominent spot on the list of products that architects, consultants and other professionals specify.
Many roofing contractors, however, are not as familiar with PVC as they are with TPO, EPDM and other low-slope roofing systems. This two-part series of articles will help close that information gap.
Part I provides a brief history of PVC’s use in roofing, discusses the environmental considerations related to PVC roofing, and highlights the performance advantages of PVC roofing systems and the types of buildings they are ideally suited to. Part II will cover the types of PVC roof membranes available and the warranty options offered.
50 Years of Solid Performance
PVC roofs debuted in Europe in the 1960s and first appeared in the United States in the 1970s. ASTM D4434 – the ASTM International PVC roofing standard and the first ASTM International standard for single-ply roofing membranes – was published in 1985 and has been updated several times since.
Some of the first-generation PVC membranes did not contain scrim reinforcement. As a result, they often did not perform well. Plasticizers make PVC roofing membranes extremely flexible and easy to work with. But over the lifespan of the membrane, the plasticizers migrate out, making it more brittle. When enough plasticizer had migrated from the non-reinforced membranes, they would often shatter and crack.
Non-reinforced PVC roof membranes were deemed not viable for use in the United States, and scrim reinforcement was made a requirement under ASTM D4434. Reinforced membranes have the weatherability to deliver long-term performance, allowing them to build a 50-year track record of successful use.
Today, there are three types of scrim-reinforced PVC roofing membrane in the ASTM D4434 standard. Each has its own set of physical performance requirements that must be met. These will be outlined in next month’s article.
PVC and the Environment
The fact that architects, consultants and other design professionals specify PVC roofs so frequently should be a strong indication to roofing contractors that they are an environmentally responsible, sustainable choice.
PVC is the only thermoplastic roofing membrane not derived 100 percent from fossil fuels. It is 57 percent salt water and 43 percent natural gas – a formula that helps achieve two important goals. First, use of fossil fuels is decreased. Second, the risk of supply chain disruptions is significantly reduced; the United States has both components in abundance, giving manufacturers ready access to the materials they need without having to rely on foreign suppliers.
PVC roofing membranes are recyclable. Scrap and old material can be used as feedstock for producing new PVC roofing membranes and in manufacturing products ranging from window frames to luxury vinyl flooring, rooftop walkway pads and concrete expansion joints. Contractors should keep the following in mind, however.
- To be recycled, the membrane cannot have adhesive on it.
- As with TPO and EPDM membranes and polyisocyanurate insulation boards, PVC membranes cannot simply be thrown into a recycling dumpster. The contractor must contract with a company to pick it up and haul it to an appropriate recycling facility.
- When a project involves tearing off existing roofing materials, the designer may specify that the old membrane and other system components must be recycled. Contractors should watch for this stipulation so they can build the recycling-related costs into their bids. (Note that this holds true when tearing off a wide variety of roofing materials, not just PVC membranes.)
Performance Advantages
PVC membranes offer several performance advantages in installed roof systems, including chemical resistance, fire resistance, energy efficiency, heat-welded seams and crew-friendly flexibility.
Chemical Resistance
PVC roof membranes are highly resistant to greases, animal fats, jet fuels, acids (particularly sulfuric acid) and other chemicals. This makes them the ideal choice for restaurants, food processing plants, airports, manufacturing facilities and other buildings where the roof will be exposed to these chemicals.
PVC is not, however, chemical-proof. Where higher levels of chemical exposure are expected, such as around rooftop vents, the membrane should be protected with a grease trap or a second, “sacrificial” layer of membrane.
Fire Resistance
PVC is exceptionally fire-resistant and is self-extinguishing once the source of the flame has been removed. It outperforms EPDM and TPO in this arena by far and will achieve steeper-slope UL fire ratings than is possible with these other single-ply options. It is ideally suited to buildings with an elevated risk of rooftop fires – such as those with solar panels or other electrical components on the roof and restaurants where there is the potential for a rooftop grease or oil fire. It also is a good choice when the building’s occupants will have greater difficulty evacuating in the event of a fire, such as senior care facilities and hospitals.
“Cool Roof” Options
Like white TPO and white-on-black EPDM roofs, white PVC roofs can significantly enhance the energy efficiency of buildings in warmer climates. They reflect much of sun’s energy away from the roof and then emit much of the energy that is absorbed back into the atmosphere. This lowers temperatures on the rooftop and inside the building, keeping occupants comfortable while reducing air-conditioning costs and helping maximize the performance of HVAC equipment.
Heat-Weldable Seams
As with TPO roofing systems, PVC sheets are welded together to create exceptionally strong, waterproof seams. If done right, the seams will be stronger than the membranes themselves.
The quality of field seams completed with automatic welders is verified with test welds. Hand-welded details are inherently more open to human error. Here, bleed-out – when the darker bottom ply of the membrane spills out of the lighter top ply slightly – is a helpful visual indicator of a strong weld.
Flexibility
PVC roofing membranes are more flexible than TPO membranes, making them easier for crews to handle on the roof.
Conclusion
Over five decades, PVC roofing systems have become a favorite choice of design professionals. Armed with a greater understanding of PVC roofing’s history, sustainability and performance characteristics, roofing contractors can be equally confident in recommending it to their customers. Options abound to meet various requirements. Part II of this series will outline those choices as well as the warranties available on PVC roofing systems.
About the Author
Tony Vieira is product segment manager for low-slope roofing manufacturer MuleHide, overseeing the company’s single-ply roofing, Poly ISO insulation, and cover boards product categories. He can be reached at Tony.Vieira@mulehide.com.
Originally Published by Roofing Contractor - Sept/2024