Charleston Roofing: Article About Built-up Roof Systems
For more than a century, most commercial roofs were covered and protected with built-up roof membranes, or BUR systems. Still a reliable roof option today, this tried-and-true method of installing a watertight roof is created by alternating layers of bitumen and reinforced felt that is then surfaced for a final layer of protection.
As you work with your reliable Charleston roofing contractor to determine the best roofing system for your business, BUR systems may be discussed. Understanding BUR roofs, how they work and how they can fail will help you engage in an informed discussion about roofing options with your professional roofer.
There are many material options with BUR membrane systems. Although asphalt is the most common bitumen used as the adhesive and watertight layer, coal tar and cold-applied adhesive can also be used. Asphalt, of course, is heated and then mopped onto the felt layer or applied with a mechanical spreader. Coal tar is applied in a similar manner. Cold-applied adhesives are not heated, but contain solvents to keep the material fluid enough to be applied to the roofing layers.
Several choices also exist for the felt plies. Most of the felts used in the layering process are made of glass, polyester or organic fibers and are reinforced to provide strength to the roofing system. Most asphalt roofs use fiberglass felt layers for the best performance.
The final decision for BUR systems is the surfacing material.
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They run the gamut from aggregates like slag, gravel and mineral granules to aluminum coatings. Surfaced cap sheets, elastomeric coatings and mopped-on hot asphalt can all be used to provide the BUR's final protective layer.
With a layered and watertight structure, BUR systems have many benefits. Foremost of these benefits is their outstanding and long-lasting protection against rain and water. The repetitive layers of asphalt and felt create excellent seals that cover nooks, divots and irregularities well, and the system works well on a number of different surface types. BUR roofs are also resistant to UV rays, have low maintenance costs and can last for many years.
The feature that provides such excellent water protection is also its greatest expense. BUR systems require a great deal of work, from heating the asphalt and spreading it onto the surface to repeatedly layering it with reinforced felt plies. As a result, the installation is arduous and often lengthy. Hot asphalt can also produce unpleasant fumes.
Other drawbacks to BUR systems involve the topmost layer of surfacing. Many of the surfacing materials do not handle foot traffic well, and they are vulnerable to high winds. Furthermore, if an aggregate-covered BUR system leaks, it can be difficult to determine where the leak is originating.
This inability to pinpoint a leak can dramatically slow repair. BUR membrane systems are just one of many types of roofs that may be appropriate for your commercial flat or low-slope roof. And while newer roofing membrane systems are available, BUR systems still have a strong place in the commercial roofing industry.