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Modified Bitumen (App)

Modified bitumen roofing is sometimes referred to as torch-down roofing, although it is actually made in two versions – one is torch-applied and one is installed using hot asphalt. These two types of modified bitumen are APP (atactic polypropelene) and SBS (styreine butyl sterine). Among commercial flat roof systems, it is probably either the second or third most commonly used system in use today in the Los Angeles area, after a traditional BUR roof system. Just like BUR roofing, modified bitumen has a long track record of performance throughout both the US and Europe – it has been used in Europe since the early 1950’s and is the most common system used in that region.

APP modified bitumen roof systems typically consist of 2-3 plies of roofing material, each applied in sequence to the roof, and adhered together by the asphalt bitumen that is heated by application of the torch – usually at 900-1100 degrees. The number of plies and type of ply material varies according the specification desired. The standard system consists of a fiberglass-mat base sheet and the APP granulated capsheet. For a longer warranty, a smooth APP membrane can be added in between the base and the granulated membrane. This system offers warranties up to 20 years and potential performance well in excess of that – making it one of the top performing systems in existence.

APP Modified Bitumen
APP Modified Bitumen

SBS modified bitumen roof systems are basically identical to a traditional BUR roof system, with the difference being the final surfacing layer of the system – the capsheet. The SBS capsheet has a much heavier polyester mat core that resists splits and tears much better than a standard BUR capsheet. It is much more pliable and has far superior elongation characteristics. Also, it is very durable because it has a specially formulated modified asphalt, impregnated in the membrane.
Both the APP and SBS membranes are about twice as thick as a traditional BUR capsheet. Their elongation is up to 20% and they have tear and tensile strengths of up to 100 lbf – this is a far superior performance. Of course, for this performance the customer will pay a higher cost. In the long run, however, the added life of the roof system outweighs the higher initial investment.

Like a BUR roof capsheet, the modified bitumen capsheet can serve as a reflective surface, to rebound incoming solar radiation from the sun, keeping the roof surface cooler and therefore reducing air conditioning costs for the building itself. These “cool roof” capsheets are designed to reduce energy usage and meet state energy saving requirements, such as Title 24, here in California. When selecting a modified bitumen roof system, it is imperative that the choice is tailored to the specific project. Consult with your Ferguson & Melvin representative for recommendations for your job.

Modified Bitumen
Modified Bitumen

SBS modified bitumen roof systems are most recommended for commercial flat roof installations, where a balance of quality and cost is the highest concern, and where asphalt fumes would not be a disruption to tenants, occupants, or students. APP modified bitumen roof systems are a good choice for either commercial flat roof or residential flat roof installations. They actually outperform the SBS roof systems in the Southern California region and are the preferred method of Ferguson & Melvin Co., provided the project is suitable. Since an open flame is used, care must be taken around any flammable areas on the structure. Also, special insurance and installer training is critical.

Ferguson & Melvin Co. supervises all of our modified bitumen roof installations and guarantees the highest level of quality and service from our staff on the roof and in the field. We strive to provide the best suitable modified bitumen roofing product, designed to meet your roofing needs.

Call our office today at (800) 974-ROOF or click here to request a quote.

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