Modified Bitumen roof systems consist of one, two, or three ply systems. The type of
substrate will often determine the type of system being installed. Modified membranes can
also be installed in conjunction with built-up roof materials (such as multiple plies of
fiberglass felt) to form a "hybrid" roof system. Modifieds have proven performance on
residential, commercial, and industrial applications.
Roofhelp recommends that all modified roofs be installed on slopes not less than
1/4" per horizontal foot (stated "quarter in twelve" or "quarter-inch slope") in order to achieve positive drainage.
In order to create roofing grade asphalt, asphalt flux is air-blown at elevated
temperatures which converts the flux to roofing grade asphalt. In the early 1970s,
the Italians, lacking the blowing equipment, were looking for a product that would convert
asphalt flux into a usable roofing product. They discovered that if Atactic Polypropylene
(APP) - a by-product of propylene polymerization - was added to asphalt then it gave the
asphalt some plastic properties. They found that by adding about 30% of APP modifier, they
could stretch the modified asphalt up to fifty percent of its original length before it
Next came the need to make it into a usable roll product. Some type of reinforcement
would be needed. They looked into various reinforcement materials and decided on a
polyester mat because polyester would accommodate the APP modified asphalts
elongation properties whereas the more commonly used woven glass mats would not. The
reinforcement material is dipped into the hot modified bitumen mix, then goes through a
rolling cylinder, cooled, and then wound into a roll.
APP membranes are applied using a torch. The back of the sheet has extra asphalt on it
which, when heated, bonds to the substrate. This was especially convenient for the
smaller, more cut up roofs because less room and equipment is needed on site to
torch-apply a membrane than is necessary for application using hot bitumen.
While APP was being looked into in southern Europe, northern Europe was experimenting
with a different type of modifier called Styrene Butadiene Styrene (SBS). The French and
Germans found that if they added 10%-15% of SBS rubber to asphalt, the asphalts
characteristics changed to those of the rubber additive. They learned that they could
stretch the SBS modified asphalt up to six times its original length and that, unlike the
APP, it would return to its original size when allowed to relax.
There are a wide range of reinforcements used in SBS roofing materials. These include
fiberglass or polyester mats and scrims, or combinations of both. The fiberglass mats
range in weight from 1.0 to 2.5 pounds per 100 square feet or around 50 to 125
grams per square meter. Polyester reinforcements range in weight from 3.5 to 5.0 pounds
per 100 square feet or 170 to 250 grams per square meter. The type of reinforcement used
depends on the materials performance requirements.
SBS membranes can be hot asphalt applied, torch applied, or cold process applied.
COAL TAR MODIFIEDS
Information coming soon!
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