I am not a professional, but have been an avid home improver and observer for more than 40 of my 60 years. During that time, every asbestos-cement roof I ever noticed is still in place and doing well. The only losses have been on houses that were demolished. In my part of the country (Houston, Texas) these shingles are virtually indestructible so far as environmental conditions is concerned. They can be broken, but unlike natural slate or tile, they are resilient enough to walk on without apparent damage.
There are many homes in the older neighborhoods in Houston and other cities in Texas that use this type of roofing. Some use very large shingles laid in a diamond pattern, with half-round ridge and hip shingles. Others take the form of thin shingles, gray, that are very similar to common asbestos siding. Yet others, such as the Supraslate, are 1/4" thick, shaped to resemble natural slate, and laid exactly like natural slate.
I reroofed my home in 1986 using Supradur brand "Supraslate" asbesos-cement slates. On my house, The slates are ¼ inch thick and each measures 9 inches wide by 16 inches long. They are laid with 6½ inches exposed to the weather, the remaining 9½ inches being covered by the slates above, making the roof not less than a half inch thick, and ¾ inch thick for the last three inches of each slate. This roof is in perfect condition today, showing no signs of wear or deterioration.
Unfortunately, due to press and political panic resulting from the widespread illnesses among asbestos workers from asbestosis and asbestos-induced lung cancer, no asbestos material is now used in the manufacture of roofing in the United States. This is unfortunate, because with use of proper protective practices, asbestos can be used safely. Existing asbestos-cement products, moreover, are in no way hazardous. The asbestos in this roofing is wholly encapsulated within dense cement, so it poses no hazard unless crushed, shredded or ground up.
To place the excellence of asbestos cement as a material in perspective, it is instructive to note that asbestos-cement water pipe carries a large part of the drinking water supply in Houston and many other large cities worldwide. This testifies to the strength, resilience and durability of asbestos cement material. Asbestos cement is also ubiquitous in older industrial buildings worldwide, where it is employed in corrugated form for fireproof roofing and exterior wall coverings.
I have heard of these roofs being called a "Johns Manville Lifetime Roof," and they certainly met this test. Roofs of this type are very common in Galveston, Texas, a city that has endured countless major storms and several extremely damaging hurricanes over the last 100 years. Nevertheless, one can see hundreds of very old builings there topped by equally old asbestos-cement roofs. Mostly these are the diamond-shaped style.
This material was made for most of the most of the 20th Century by the Johns-Manville Company, which in the early 1980’s (I believe) conveyed at least part of its production assets and know-how to the Supradur Company.
Both companies are now bankrupt due to asbestos litigation, and manufacture of asbestos products is not banned in the United states.
While it is no longer possible to install a new roof of this kind, the existing ones should outlast all of our lives.
Exactly what could an insurance company object to? The material is fireproof, rot proof, leak proof and permanent. It is highly resistant to hail damage. This is really mystifying to me.