Flat Roofing Systems

Membrane Roofing Systems

Membrane roofing is a flat type of roofing system for buildings that can be found all over the Fox Valley area. It is used on flat or nearly flat roofs to prevent leaks and move water off the roof. Membrane roofs are most commonly made from synthetic rubber, thermoplastic (PVC or similar material), or modified bitumen (“torch down”). These types of materials have become the replacement for asphalt roof systems, which is an older, less effective type of flat roofing system. Membrane roofs are most commonly used in commercial application, though they are becoming increasingly more common in residential application.

Contractors and engineers will choose a type of membrane roofing based on the requirements of the job and the attributes of the material. Costs for membrane roofing can range from as little as $125 per square (100 square foot area), to $350 per square or more. Membrane roofing systems consist of not only the membrane itself, but also any insulation, flashing, roof accessories and sealants.


Built-up Roofing (BUR)

Built-up roofing, or BUR for short, consists of layers of organic/inorganic felts saturated with liquid asphalt or coal tar. BUR has been providing reliable protection against the elements for many years.

The layers are installed in an overlapping fashion; each layer is referred to as a ply. Applications can consist of 2 plies, or as many as 5 plies or more. Commonly referred to as a Tar & Gravel roof, the uppermost surface is often topped with small stones to provide additional protection from damage and UV degradation.

Modified Bitumen, Mopped & Torch Downs

Modified bitumen membrane roofing is essentially a pre-manufactured, built-up roofing system. Thick layers of reinforcing felts and liquid bitumen are bound together in the manufacturing facility and shipped to the job site in roll form. Chemical modifiers enhance the attributes of the liquid bitumen to make it suitable for job conditions.

Modified bitumen roofing can be applied in a method similar to built-up roofing, by using hot liquid bitumen that is mopped in place, or it can be installed by torching it down. As the roof membrane is being unrolled, a worker uses a torch to melt the leading edge of the roll into a liquid that acts as a binder to hold the material down.

Thermoplastic Olefin (TPO)

Thermoplastic Olefin, commonly called TPO, are plastic sheets welded together with hot air creating one continuous membrane. These components can be re-welded, with the exception of CSPE, making repairs easy to administer. These traits lend themselves well to both large and small roof applications because of the hot air versus torch down welding.

TPO is a single-ply roofing system consisting of a Thermoplastic Polyolefin membrane. The TPO membrane is typically comprised of three layers: a polymer base, a strong, polyester-reinforced fabric center (scrim) and a tough thermoplastic polyolefin compounded top ply.

Other Types of Membranes

Other types of membrane roofing such as chlorosulfonated polyethylene (CSPE), ethylene-propylene-diene-monomer (EPDM), polyisobutylene (PIB), and polyvinyl-chloride (PVC) consist of large sheets of material that are joined together using various chemical or thermal methods.

Primers and adhesives can be used along overlapping edges to form an impervious joint between sheets, or heat welding can also be utilized to turn all the pieces into one large roof covering.

The large sheets are then applied to the roof surface by using one of several methods. A ballasted roof uses the weight of stones or blocks of concrete, similar to pavers, to hold the roofing in place. Strips of metal fastened to the structure at all edges and seams can also be used. Another popular method is to use an adhesive that is similar to contact cement to hold the sheets down.

Advantages Over Asphalt Flat Roofing Systems

The application types of membrane roofing listed above have distinct advantages over the previous flat roofing method of asphalt and gravel. In asphalt and gravel applications, it can be very difficult to create a proper seal at all seams and connection points. This can cause many roofs to leak early in a lifespan , and require more intensive maintenance.

When installed correctly, newer materials are either totally seamless, or have seams as strong as the roof body. The primary concern people have with flat roofing is leakage, and the newer systems should eliminate many of those issues

Repairs for asphalt and gravel roofs can be difficult, mainly because it can be hard to locate the exact point of a leak. Newer systems can be patched relatively easily, and cracks and leaks are easier to locate.

Originally asphalt roofing required a layer of gravel as the top layer for two reasons. First, asphalt with direct exposure to sunlight degrades faster, due to the expansion and contraction and the damage created by UV rays. Second, asphalt needs the gravel weight on it to hold down the roof because it “sits” on the top of a building, instead of being attached to it.

Each of the three newer types of membrane roofing systems contain materials that resist expansion and contraction, and have advantages against UV rays. Also, because these membranes have strong seams, when normal expansion and contraction does occur, its damage to these seams is exponentially reduced. Best of all these newer roofing systems are also attached directly to the top of a building, which eliminates the need for excess weight, and greatly reduces stress on your structure.


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