In the mid-1970s, the worldwide oil crisis was having a degrading effect on the quality of asphalt available for conventional built-up roofing (BUR) systems. Around that same time, natural fabrics were being replaced by synthetics, compromising the quality of rag-felt scrims used to reinforce BUR systems.
These factors were the driving force behind America’s evolution toward a European concept in roofing: modified bitumen technology. Modified bitumen roofing resolved both problems by pre-manufacturing the cap sheet of BUR systems to improve the quality of the bitumen (asphalt), and by introducing innovative synthetics to improve the quality of the scrim.
The idea behind modified bitumen roofing is a simple one: By pre-manufacturing the cap sheet component of BUR systems in controlled factory environments, material suppliers could add polymer modifiers that improve the performance of multi-ply roofs, which had traditionally been fabricated in the field. Today’s high-performance polymer modifier technology is selectively targeted at enhancing increasingly specific performance attributes, such as low-temperature flexibility or ultraviolet-radiation resistance.
Similarly, yesterday’s cotton felts have given way to high-strength alternatives such as fiber glass and polyester. Still, the general concept remains the same: controlling the composition of the asphalt and scrim to improve rooftop performance.
Built to Last
Durability is the most significant performance advantage of modified bitumen roofing. Not only do the modifiers improve the roof’s ability to withstand foot traffic and other abuses, they help roofs age more gracefully. Unlike other less resilient commercial roofing options, modified bitumen roofs lend themselves to restorative alternatives as they age, delaying the need for tear-off and reroofing. With vigilant monitoring and routine maintenance, modified bitumen roofs remain watertight for decades.
For owners who anticipate holding onto their properties for 30 years or more, or for applications such as facilities that are subjected to abuse, modified bitumen roofing is a popular alternative. When you look at the numbers, it’s easy to see why.
Roofing materials generally constitute a very small portion of the total installed cost of roofing. By upgrading the material to a pre-manufactured, multi-ply modified bitumen solution, reroofing costs are typically reduced significantly over the life of the building. The modest increase in initial costs, due to higher quality materials, is typically returned many times over through added years of service life.
Selection Criteria
Specific modified bitumen roofing solutions are differentiated by those performance attributes they are designed to achieve. The primary factors defining performance are the:
- Type(s) of polymer modifier(s) - for example, styrene-butadiene-styrene (SBS).
- Amount of modifier used - as a general rule, more is better.
- Effectiveness of polymer dispersion in the manufacturing process.
- Reinforcement methods such as fiber glass, polyester, or combination fiber glass-polyester scrims.
- Adhesion methods such as hot asphalt, cold adhesive, self-adhering, or torch application.
High-performance modified bitumen roofing solutions can be performance-specified to achieve a highly specific array of application-driven attributes, including many of the sustainability characteristics critical to today’s smart buildings.
Brian Lambert is director of marketing for The Garland Co. Inc. (www.garlandco.com), a Cleveland-based manufacturer and distributor of high-performance solutions for the building envelope.
