The EPDM seam debate

Unlike seams on thermoplastic roofing membranes such as TPO and PVC, which are welded using hot air, seams on standard EPDM roofing membranes are chemically bonded together using tapes and primers. This cold bonding process results in a seam that is continuous, flexible, elastic, strong and durable.

There is, however, a certain industry stigma that states that seams are the weakest part of an EPDM roofing system.

This reputation dates from the early decades of EPDM installation, when seams were bonded using liquid adhesives. This process was very sensitive to environmental variables (atmospheric humidity, etc) and relied a lot on the skills of the installer. Too much or too little adhesive, a flash-off time that was too short, not enough or uniform pressure applied to the seam… all this could compromise the quality of the bond.These early adhesives were also the subject to oxidation and eventual brittleness. Over a 15-20 year cycle, these liquid-applied seams often became the primary point of failure. This created the narrative that while the EPDM membrane itself could last several decades, the roofing system was only as good as the glue holding it all together.

One of the most significant advancements in the history of EPDM roofing was the widespread adoption of seam tapes in the 1990s, which remain the standard ever since. These tapes are composed of a highly engineered EPDM-based polymer that undergoes a chemical cross-linking process when pressed into the primed membrane. Through this process, a chemical exchange occurs at a molecular level. In addition, the membrane surface is mechanically interlocked by the components of the primer. Both mechanisms create high-resistance molecular links that provide the seam with incredible strength for several decades.

Besides creating a strong seam, this system offers several additional advantages. To start with, no electricity or costly machinery are needed. The risk of mistakes is therefore limited, as the quality of the seam does not rely on the performance of the machinery or on its settings (temperature, speed, pressure, etc.) which must be adapted to the changing weather conditions.

In addition, field splices made with seam tapes are easy to visually inspect after installation, and are also easy to repair if needed. A seam that was made over 30 years ago can be cleaned, primed and reinforced with a new layer of cover strip or tape, effectively resetting the clock on that joint.

On actual warranty claims, the weakest link of any roofing system (EPDM or otherwise) is rarely the field seam. Instead, failures typically occur at flashings and terminations (for example where the roof meets a wall or a pipe), are the result of mechanical damage, or of substrate movements that exceed the elongation limits of the roofing system.

Lack of skilled labour and proper training can also have a big negative impact on the long term performance of the roofing system. For property owners, this can translate into skyrocketing maintenance costs and voided warranties. Ultimately, a "cheap" installation by an unskilled crew can lead to a full replacement years before the membrane's expected lifespan.

At Elevate, we strongly believe that technical proficiency is the most vital component of any flat roof. High performance demands expert installation, that is why we require contractors to complete specialized training programs on our roofing systems. These are regularly organised by our local partners at various facilities across the regions.

We empower contractors through a combination of progressive educational courses that scale from beginner to advanced level and direct on-site support from our technicians, who provide assistance at job start, technical advice and inspections. Furthermore, our comprehensive technical resources are immediately available for architects and specifiers, such as step-by-step manuals, BIM Objects, installation videos, roofing system selection guide, detailed system drawings, etc. Ultimately, we provide more than just a membrane; we deliver the entire ecosystem of support necessary for a flawless, long-lasting installation.