Modified Bitumen Roofing
Modified Bitumen roof systems are asphalt based and provide superior waterproofing characteristics. The lifespan for this type of roof is typically between 10 and 20 years. Modified Bitumen roofs are usually installed as a fully adhered, two-ply system. They are made of asphalt that’s been modified with a polymer to create either plastic or rubber like properties. These modifiers provide added resistance to brittleness and extreme temperatures. They also increase the elasticity and strength of your roof. The most common modifiers used are Atactic Polypropylene (APP) and Styrene Butadiene Styrene (SBS).
APP (Atactic Polypropylene): APP provides a plasticized quality to the asphalt. Adding this modifier allows the asphalt to be stretched up to 50% of its original length. APP is reinforced with a polyester mat and manufactured into a rolled product. Extra asphalt on the backside allows it to bond to the substrate through heat welded or torch application.
With torch application an open flame torch is used to melt the bottom side of the sheet as its being applied. Heat welded application involves using a welder to blow out hot air which fuses the back side of the membrane to the substrate during application.
SBS (Styrene Butadiene Styrene): When the SBS modifier is combined with asphalt it produces rubberized properties. Adding SBS makes it possible for asphalt to be stretched up to six times its normal length. Once its relaxed it can return to its normal length. This helps your roof deal with the stresses of normal expansion and contraction. Reinforcement materials for SBS include fiberglass, polyester, or both. SBS membranes are usually applied with hot asphalt, cold adhesive, or as a self-adhering SBS membrane with an adhesive backing.
During hot asphalt application, hot asphalt acts as an adhesive. It’s applied to the substrate and the membrane is then laid over the hot asphalt. The cold adhesive method uses specially formulated asphalt adhesives applied to the substrate, while the self-adhering SBS has an adhesive on the membrane itself which is exposed by removing a release paper.
Numerous surfacing options are available for APP and SBS modified roofs. These include factory applied mineral surfaces, gravel surfaces, smooth surfaces, and “cool roof” coatings, which are highly reflective coatings that can help save on cooling costs.
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