This post originally appeared on the Buildings Buzz blog.
Low-slope roofing technology is perpetually evolving, and architects, contractors, and roof system manufacturers are continually trying to differentiate and improve their products and services. From 1850 to 1950, virtually every low-slope roof was a built-up roof (BUR), an old but proven system with alternating layers of asphalt or coal tar (bitumen) and reinforcing fabric, surfaced with aggregate (gravel or minerals). By 1980, an advancement known as a modified-bitumen system, consisting of rubber or plastic polymers combined into bitumen on a reinforced scrim between more layers of hot bitumen, began gaining prominence. The evolution of these polymer technologies eventually incorporated SEBS and SIS modifiers to improve UV resistance, which is known to extend rooftop longevity. Today, the next big breakthrough in roofing technology may be the infusion of urethane as the modifier in modified-bitumen membranes.
Urethane technology itself is nothing new. Urethane has been a durable, reliable, and proven material since the beginning of World War II, when it was created as an improved substitute for rubber, which was in short supply due to the war effort. Soon after the war, urethanes were being used in a multitude of commercial adhesives and coatings. However, it was not until European countries were experiencing an inordinate amount of rutting and cracking in their roadways that urethane was first used as an asphalt modifier. As with paving, the roofing industry utilizes asphalt as its primary binding agent and adhesive. In 2009, Europe’s premier scientists discovered that modifying asphalt with a urethane polymer prevented traffic-rutting, low-temperature cracking, moisture cracking, and fatigue cracking.
With traditionally-modified asphalts, the oils within the asphalt heat up in the sun and inevitably “cook out”, resulting in a dry, cracked surface. Urethane molecules, on the other hand, form a continually strengthening chemical link with one another over time, resulting in a modified-asphalt surface that actually becomes more resilient over time. These same chemical properties are even more relevant and effective when it comes to roofing materials, as roofing membranes contain about 10 times the asphalt content of a road.
In addition to enhanced UV resistance, advanced testing has also proven that urethane-modified membranes attain greater adhesion levels of surface aggregate to the actual membrane, which enhances a roof’s weathering capabilities. Also, urethane-modified membranes have shown noticeably higher chemical resistance properties, allowing it to more effectively combat exposure to common rooftop chemicals such as compressor oil and animal fats. Without protection against these elements, roofs are susceptible to corrosion, eventually leading to cracking, leaking, and ultimately system failure.
Although urethanes are a relatively new advancement to the roofing industry, they have been historically synonymous with durability and strength. Urethane products are already relied upon in a variety of other high-stress applications, including the construction and aerospace industries. Considering all of the potential advantages that urethane-modified roofing membranes offer – and the fact that building owners are perpetually searching for more durable, longer-lasting roofing options – urethane-modified bitumen may very well be the next big step in the evolution of roofing technology.