Roofing Article

Consumer Roof Info, Roofing Products

Membrane Roofing Systems

Membrane roofing is a type of roofing system for buildings. 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, 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, 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 much as 5 plies or more. For what is referred to as a Tar & Gravel roof, the uppermost surface is often topped with gravel or small stones to provide protection from physical 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 the 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, or TPO, are plastic sheets welded together with hot air creating one continuous sheet membrane. Can be rewelded with the exception of CSPE. Lends itself well to both big box and small roof application because of its hot air weldability.

TPO is a single-ply roofing system consisting of a Thermoplastic Polyolefin membrane. The TPO membrane typically comprised of three layers of a TPO 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 chlorosufonated 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 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 show distinct advantages over the previously more common flat roofing method of asphalt and gravel. In asphalt and gravel application, 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 its lifespan, and require much more maintenance.

When installed correctly, newer materials are either seamless, or have seams as strong as the body. This eliminates much of the leakage concerns associated with flat roofing systems.

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

Originally asphalt roofing required a layer of gravel above it for two reasons. First, asphalt with direct exposure to sunlight degrades much faster, mainly due to the expansion and contraction throughout a day, and also the damage created by UV rays. Second, asphalt needs weight above to hold it down, 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, as well as reflect much of the UV rays. Also, because these membranes are either lack seams or have strong seams, what expansion and contraction does occur does not create leaks and breaks at these seams. These newer roofing systems are also attached directly to the top of a building, which eliminates the need for excess weight above.