How To Look At A House
McGarry and Madsen's home inspection blog for buyers of
site-built, mobile/manufactured and modular homes
What is the life expectancy of an asbestos cement shingle roof?
Wednesday, June 27, 2018
The life expectancy of an asbestos cement shingle roof is 40 to 60 years, with an average of 50 years. It will last longer with luck and diligent maintenance, and we saw one roof a few years ago that was just beginning to fail at 60 years old. The roof shown in the photo above and the first one below is 37 years old. But there are also four factors that can shorten the life expectancy:
- Insurance - Many insurance companies will not write a policy on a home with an asbestos cement roof. The roof may need to be replaced to get reasonably priced insurance.
- Maintenance - Asbestos cement shingles are somewhat brittle. They are installed in a similar way as slate, and are easily cracked or fractured when walked on by someone not familiar with the material. Professional maintenance is usually done from a roof ladder hooked over the ridge to avoid damaging the shingles, making it more time-consuming and expensive.
- Marketability of the Home - When some homebuyers see the word “asbestos” in the disclosure sheet on a house, they walk.
- Safety - The asbestos fibers that cause mesothelioma and several other cancers are embedded in the cement of the shingle. They are not harmful unless the shingle is broken and the fibers become released into the air, at which time they become what is technically called “friable” and dangerous.
Theoretically, you could just leave them alone and everything would be fine. But pieces of shingles crack off and fall to the ground at an increasing rate as the roof ages and the material becomes more brittle. The broken shingles can be replaced by scavenging intact shingles from a less visible part of the roof to replace them, but you still have to contend with bits and pieces of asbestos-containing material that are deteriorating on the ground around your home.
Asbestos was a “wonder” material at the height of it’s popularity in the 1930s and, like kale in grocery stores today, seems to have been inserted into everything to make it better. The fibers really do have amazing qualities of heat resistance, rot resistance, chemical stability, and tensile strength. it’s just that asbestos can make you very sick, and it takes up to 20 years for the symptoms to appear after exposure.
One potential solution to an aging asbestos cement roof is to leave it in place and apply an SPF (Spray Polyurethane Foam) roof over it, like in the example below that we recently inspected in Gainesville.
Here’s a bar graph that compares the life expectancy of an asbestos cement shingle roof to other types of roof coverings.
Go to our blog post What is the average lifespan of the parts of a house? for rating of other house components. To understand the basis, potential use, and limitations of lifespan ratings, see our blog post ”How accurate are the average life expectancy ratings of home components? Are they actually useful?”
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To learn more about roofs and attics, see these other blog posts:
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