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Cement Asbestos Roofing

William Kibbel III, The Home Inspector

We looked at a house that has what we thought was a slate roof. Later, we were told it is asbestos. I was aware of asbestos siding, but not roofing. The house is 60+ years old, could this be original? Is it a major health concern to live in a home with asbestos on it? How long do they last? Do they need maintenance?

By the time the roof that you saw was installed, cement asbestos roofing and siding was well known in the building industry as a durable, inexpensive material used to cover and protect buildings.

The Background

Experiments were conducted in the 1880s using asbestos fibers in mixtures that resulted in building products like insulation for steam pipes and boilers. The fibers were eventually mixed with Portland cement and the "paste" was used as roof repair compound. In 1907, process equipment was invented that produced rigid sheets from the cement asbestos. These sheets could be pigmented and cut into manageable shapes, and were able to have textured patterns pressed into the surface. The result was very durable siding and roofing shingles that imitated traditional natural products--both less expensive and lighter than slate. They don't rot or warp like wood, and are very fire resistant. I'm not at all surprised about the popularity of these asbestos sheets throughout two-thirds of the twentieth century.

Manufacturers of individual asphalt shingles, less expensive and more flexible then cement asbestos, were major competitors for market share in the roofing material industry by the 1920s. In the late 1930s, asphalt strip shingles, coated with granules in a wide variety of colors, were the most popular roof covering.

The Risk

Asbestos is made up of microscopic mineral fibers that when inhaled into the lungs can cause serious respiratory disease and cancer. Asbestos containing products, like cement asbestos roofing and siding, have the fibers imbedded in the Portland cement, and there is little health risk if the material is in good condition and not disturbed. Severely worn or damaged roofs and walls, or improper repairs, alterations, or removal can allow release of the fibers and risk the health of the occupants and neighbors. The EPA provides detailed information about managing asbestos containing products on its web site.

The Problems

Cement asbestos roof shingles typically have a much shorter life than the siding panels. The thinner shingles, about an eighth of an inch thick, typically last about 50 to 60 years. The thicker ones are about a quarter of an inch and I've seen them last 70 to 85 years. When the roofing shingles get very old, they often become less impervious to water and it's common to see moss growth. Shingles absorbing water also have a tendency to break during freezing weather.

If replacement is needed, removal can be a significant expense. If the shingles are severely weathered, to the point that the material can be crushed by hand, professional abatement is needed. Precautions should still be taken even if they're intact. The fasteners securing them should be extracted, rather than prying up the brittle shingles. The material should be kept wet and lowered to the ground instead of being tossed down. Individual states and municipalities may also have additional requirements for removal and specific requirements for disposal.

Like tile and slate roofs, occasionally there may be some cracked, broken, or missing shingles, or flashing repairs that may be needed. Maintaining an asbestos tile roof can also be difficult. Finding contractors willing to work with material associated with the "A" word can be a challenge. It can also be a challenge to find contractors that are mindful of the brittle nature of these shingles. Too often minor repairs have lead to widespread damage when Bubba the handyman marched across a fragile roof in steel-toed boots.

I have found that some roofing contractors, experienced with slate and tile roof repairs, are willing to repair and restore cement asbestos tile roofs. The tools, equipment, and techniques they use for their "regular" repairs are well-suited for working with these brittle shingles. There are also a few good sources of salvaged replacement shingles that with luck can be a close match to the existing roof.

Hopefully, the remaining cement asbestos roof tiles are in good to repairable condition, and will be properly maintained for their maximum potential life. Those that are beyond safe repair will need to be properly and professionally removed, and will likely be replaced with a roof that looks like most other roofs, and will likely only last one-third as long.

About the Author
William Kibbel III is a home inspector and restoration consultant specializing in historic residential and commercial buildings. He is vice president of Tri-County Inspection Company, serving Southeastern Pennsylvania and Central New Jersey.

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