What is Transite Siding?

Transite originated as trade name that The Johns-Manville Corporation created for a line of asbestos-cement products, including boards and pipes. In time it became something of a generic term for other companies’ similar asbestos-cement products, and later an even more generic term for a hard, fireproof composite material, fiber cement boards, typically used in wall construction.

The use of asbestos to manufacture transite was phased out in the 1980s. Previously transite was made of cement, with varying amounts (12-50%) of asbestos fiber to provide tensile strength (similar to the steel in reinforced concrete), and other materials. It was frequently used for such purposes as furnace flues, shingles, siding, and wallboard for areas where fire retardancy is particularly important. It was also used in walk-in coolers made in large supermarkets in the 1960s, 1970s and even the 1980s. Other uses included roof drain piping, water piping, sanitary sewer drain piping, and HVAC ducts. Because cutting, breaking, and machining asbestos-containing transite releases carcinogenic asbestos fibers into the air, its use has fallen out of favor.

The transite that is produced today is made without asbestos. Transite HT and Transite 1000 are currently available fiber cement boards that do not contain asbestos. Instead they contain crystalline silica which has been classified by The International Agency for Research on Cancer (IARC) as being carcinogenic to humans (Class 1). Crystalline silica is also known to cause Silicosis, a non-cancerous lung disease. Demolition of older buildings containing transite materials, particularly siding made from transite requires special precautions and disposal techniques to protect workers and the public.