Modified Bitumen Roofing Systems
Modified bitumen roof membranes are made from either APP (plastic) or SBS (rubber) modified asphalt with polyester and/or fiberglass reinforcement scrims. The Modified Bitumen Roof Membrane can be installed torch applied, where the back of the sheet is heated with an open flame and welded to the base ply, hot applied with hot asphalt or fully adhered with a cold adhesive. The Modified Bitumen Roof Membrane comes with a granulated surface in various colors or smooth surfaced-usually finished with an aluminum reflective coating. Modified Bitumen Roof Membrane are used as cap sheets with the built-up roof systems as well.
In Europe, where modified membranes were first introduced, they were installed with a two ply application method. The American manufacturers specified a single ply application to be competitive with others roof systems and performance has been mixed depending on attention to detail in the installation and application conditions such as roof slope, ponding and runoff restrictions. More stringent requirements addressing these conditions have been implemented in recent years and more manufacturers and roofing companies are specifying multiple ply applications with the Modified Bitumen Roof Membrane.
The Modified Bitumen materials make an excellent roof with the right application specifications and sufficient attention to detail. Click here for technical information.
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Bitumen, also known as Asphalt, is a sticky, black and highly viscous liquid or semi-solid that is present in most crude petroleum and in some natural deposits, it is a substance classed as a pitch. Neither of the terms Asphalt or Bitumen should be confused with tar or coal tars.
Polymer-modified bitumen or modified bitumen (MB) sheet membranes were developed in Europe in the early 1960s and have been in use in the U.S. since the mid 1970s. Polymer-modified roof membranes are composed of reinforcing fabrics that serve as carriers for the hot polymer-modified bitumen as it is manufactured into a roll material. MB roof system membranes are composed of multiple layers, much like BUR membranes. MB roof systems typically are installed as a two-ply system and almost always are fully adhered.
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 asphalt’s 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.
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 material’s performance requirements.
SBS membranes can be hot asphalt applied, torch applied, or cold process applied.