One of the many evolutions in the roofing industry has been the formulation of modified bitumen membranes. As the name implies, modified membranes are asphalt based with modifying polymers introduced during the manufacturing process. The most common modifiers are APP or SBS, which when combined with asphalt, give the resulting membrane plastic or rubber-like properties.
In addition to providing greater tensile strength and elasticity, the introduction of these polymers allows for a single roll with coverage of 100 square feet, including the surfacing, resulting in significant labor savings during application. Modified can be installed with conventional hot asphalt, modified adhesives, open flame torches, hot air welders or most recently, self adhered. Several of today’s systems, such as Derbigum, combine the superior uplift of adhesives with the immediate watertight lap provided when torching or heat welding.
All modified bitumen membrane rolls rely on an inner scrim or reinforcement mat to hold the asphalt in place. Scrims are typically polyester or fiberglass or both and these mats are dipped into the molten modified mix, processed through a rolling cylinder and then a surfacing table and cooking bath. These mats are chosen because of their ability to accommodate the modifying polymers elongation properties. The type and weight of the mat determines the final characteristics of the roll and ultimately the price.
Since the introduction of modifieds in Florida in the 70’s, their market share has increased steadily culminating in almost 30 per cent in the 90’s. Several factors play a role in the recent decline seen in this market over the last decade. A few of these include:
- Widespread acceptance of thermoplastic systems requiring minimal slope with accompanying reduced installation cost.
- Increased insurance costs associated with open flame and 500 degree molten asphalt for SBS cap sheet installation.
- Rising petroleum costs translating to higher manufacturing prices and ultimately more expensive end user cost.
- Increased demand for environmentally sensitive “cool roofs” and more awareness of potentially harmful fumes.
Despite the items listed above, modifieds have proven performance on residential, commercial and industrial applications. The granular surfacing requires no costly maintenance coatings while making inspections and repairs very easy. Tough and long lasting, these systems are designed for Florida Owner/Managers that wish to keep and maintain rather than sell..
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