Asbestos Cement Siding

Asbestos cement siding was a commonly used building material in the US and Canada from the early to mid/late 20th century (roughly from the 1920s to the 1970s). Also simply called asbestos siding, asbestos cement siding was manufactured by adding asbestos fibers (which are a naturally occuring mineral) to Portland cement.

The resulting combination was then formed into a variety of siding shingle sizes, profiles, and textures and allowed to harden. Asbestos cement siding was a popular siding material as it was relatively inexpensive to make and was very durable. Unlike wood siding, asbestos cement siding was impervious to weather, termites, and rot, and the addition of asbestos made the siding very fireproof and durable. It’s not uncommon to find 70 year old asbestos siding still on the exterior of homes that is in perfect condition, completely unharmed by the passage of time.

The problem with asbestos cement siding (and why it’s no longer used in building materials of any sort) is that it was discovered that inhaling airborne asbestos fibers can cause cancer, asbestosis, and other lung damage. This discovery was doubly unfortunate as it came after decades of use of asbestos in building materials, so many homes built prior to 1970 contain asbestos in some form or another, but most commonly in the form of asbestos cement siding.