Asphalt-Based Flat Roofing

As we know, oil repels water. That is the basis of asphalt-based flat roofing. Most asphalt-based flat roofing consists of two or more plies of roofing that are staggered so that joints do not align. The roof is rolled-out and attached or adhered to the substrate. Substrates can be some form of wood or concrete, as well as insulation and specialty boards designed for the application of these products.

Asphalt-based roofing comes in several forms. They are thicker than single-ply roofing, and can be relatively simple to maintain and repair. They have a variety of warranties and lifecycles, from 12 to 30 years.

Asphalt composition shingles are made with a fabric mat, which is then overlaid with an asphalt blend. Once the asphalt and mat are manufactured, protective ceramic granules are embedded in the surface to offer attractive coloring, but most importantly, to protect against UV light. Differences in this process affect the life expectancy, look, and maintenance requirements of asphalt composition roofing.

Built-up or hot tar roofing is one of the oldest flat roofing systems available. It is made when layers of woven fabric are rolled out and 500-degree asphalt is mopped, by hand, onto the fabric. Multiple plies of fabric and asphalt create more strength and durability. These roofs can last a very long time, but few plies also mean they may have a relatively short life.

These roofs are often surfaced with aggregate (stone) or a granulated cap sheet for UV resistance and longevity. They can also be surfaced with a reflective coating to preserve their life.

Built-up roofs are “monolithic,” meaning the installation process eliminates seams from the roof system. Having no seams means less failure points. These roofs typically fail at the edges or penetrations.

Although Built-up roofs typically have long life spans, they are not as reliable as they once were. High insurance premiums, lower reliability of modern asphalt products, and nasty smells during installation have made them costly and often less desirable. A lessening number of workers are happy with the minor burns and messy work environment the hot, sticky tar provides. Therefore, fewer companies are willing to provide this roofing service. Still, it remains one of the better products, if installed correctly.

S.B.S. self-adhered modified asphalt roofing is a rubberized, multi-ply membrane that does not rely on heat or sticky tar for installation. This roofing is laid down in two or more plies. It has a release film backing that is removed, and it “self-adheres” to the surface it is installed on. It is installed on a surface with a minor slope, or positive drainage.

S.B.S. is a great northern climate product. It can handle a broad variety of temperatures, and has a rubber in it that allows for expansion and contraction. It is relatively thick, has a granulated surface, and comes in a variety of different colors. These roofs will last between 18 and 30 years, and sometimes more.

“Torchdown” roofing, or “A.P.P.”, is a plastic-modified asphalt roofing that comes in a roll. It is melted together in two or more plies. The name “torchdown” comes from the use of the wide-open flame that is used to melt the roofing in-place. This is a common roof in the Northwest, as product cost is inexpensive. However, it is not known for excellent life expectancy in northern climates, and most structures in the Northwest are wooden construction. Many roofing companies and customers hesitate to use this roofing, as wide-open flame on wooden structures always creates a threat of fire. It still remains popular due to tradition and low cost.