Modified Membranes

Polymer modified membrane roofing provides increased elongation and resilience. Changes in the chemistry of the asphalt improves performance. Heat welding APP membranes introduces heat right at the point of application allowing subtle temperature adjustment as required.






Increased design flexibility

Stringent quality control enforced during the manufacturing process

Increased thickness (120-200 mils) over single ply system (45-90 mils)

Improved physical properties

Ease of application

Compatibility with traditional BUR systems (for re roofing) and repairs

Successful performance experience

    Today’s specifiers, architects, and building owners need to know what to ask for and how to ask for it when designing and specifying roofing systems. Modified bitumen membrane systems bring a flexibility in design criteria never before available.

    Most modified bitumen membranes are manufactured using one of two bitumen modifiers: styrene-butadiene-styrene (SBS) or atactic polypropylene (APP).

    By adding SBS or APP in the appropriate quantity, a high quality bitumen blend can be created. The architect, specifier, and building owner must know the expected performance characteristics that the manufacturer designed into the membrane. The general physical characteristics that modifiers such as SBS or APP impart to the membrane should also be understood by the building owner, specifier, and architect:

Source: ARMA Asphalt Roofing Manufacturers Association





    APP is a thermoplastic polymer which forms a uniform matrix within the bitumen. The matrix enhances the bitumen’s physical properties by increasing the bitumen’s ultra-violet light resistance, increasing the flexibility of the bitumen at high or low temperatures and resisting water penetration.

    APP also raises the softening point of the bitumen to about 300 degrees Fahrenheit, high enough to prevent softening and slippage of the membrane even on sloped roofs exposed directly to the sun.

    APP modified membranes are generally applied using a propane torch. Applicators use the heat to soften the modified bitumen on the underside of the membrane. The membrane’s bottom surface becomes a molten adhesive which is rolled down on the substrate and then cools to form a waterproof adhesive bond. Since hot asphalt or cold process adhesives are not needed for application, APP systems are specified for commercial projects where kettles of bitumen are impractical. APP modified membranes without factory applied surfacing (granules) may need a coating depending on geographical location and life expectancy.

    SBS modifies the bitumen by forming a polymer lattice or matrix within the bitumen. The resulting blend, when cooled, acts somewhat like rubber. SBS modified membranes resist water penetration and they stretch and recover well even at cold temperatures. Because of the flexibility of the SBS modified membrane, specifiers often use the SBS membrane when they anticipate movement or deflection of the underlying deck.

    Most SBS modified membranes are generally mopped in hot asphalt, self-adhered or adhered with cold process adhesives. Some membranes can be heat welded. All SBS modified bitumen membranes that do not have factory applied mineral (granule) surfacing should have some form of ultra-violet protective coating or foil.