Asbestos Cement Siding Shingle

Asbestos-cement siding shingles are rigid, flat or textured panels manufactured by compressing a mixture of Portland cement and chrysotile asbestos fibres, typically 12 to 15 per cent by weight, into decorative profiles designed to mimic wood grain, stone, brick, or scalloped patterns. Produced from as early as 1910 and manufactured in large quantities through to 1986, these shingles became one of the most ubiquitous exterior cladding materials in North American residential construction.

The shingles were available in a remarkable variety of profiles and textures. The most common styles include woodgrain (simulating cedar clapboard), waveline (with a wavy lower edge), straight-edge (smooth rectangular panels), shake (mimicking wood shake), wide-space (with deep horizontal shadow lines), and brick-type (embossed to look like brick courses). They were typically 12 by 24 inches or 9 by 32 inches and installed in an overlapping pattern with concealed nails. Their popularity stemmed from their fire resistance, rot-proof properties, dimensional stability, and the fact that they never needed painting, though many homeowners chose to paint them.

At the peak of production in the 1950s, an estimated 30 manufacturers in the United States alone were producing asbestos-cement siding shingles. Major producers included Johns-Manville, Flintkote, CertainTeed, GAF, Bird & Son, Keasbey & Mattison, and National Gypsum. The product was marketed heavily to homeowners as a modern, maintenance-free alternative to wood siding, and it was commonly installed on new construction as well as re-siding projects over existing wood clapboard.

When intact and undisturbed, asbestos-cement siding shingles are non-friable and present a relatively low health risk because the asbestos fibres are tightly bound within the hard cement matrix. The danger arises during removal, renovation, or demolition. Breaking, sawing, drilling, or sanding the shingles releases respirable asbestos fibres. Even the act of prying shingles off a wall can snap them, creating fibre-laden dust. Power tools should never be used on these materials. Older shingles that have become weathered and chalky on the surface may also release low levels of fibres through normal erosion.

Homeowners who suspect their siding contains asbestos should not attempt removal themselves. A licensed asbestos inspector can confirm the material through sampling and laboratory analysis. If removal is necessary, it must be carried out by a certified asbestos abatement contractor who will carefully pry each shingle intact, keep materials wet to suppress dust, and package waste in labelled, sealed containers for disposal at a licensed facility. In many cases, it is safer and more cost-effective to install new siding over the existing asbestos shingles, encapsulating them in place.