Vermiculite is a silver-gold to gray-brown mineral that is flat and shiny in its natural state. When heated to around 1000 degrees C, it pops (or puffs up) which creates pockets of air. This expanded form, and the fact that vermiculite does not burn, made the material suitable as an additive, for example to potting soil. It also made a good insulating material.
If your home was built or renovated before the 1990s, it is difficult to guess the method of insulation chosen as there were numerous options: fiberglass batt insulation, blown in cellulose, sprayed polyurethane foam or even vermiculite.
Vermiculite insulation was a popular material in the 1940s and continued with the energy crisis into the mid-1980s. In Canada, it was one of the insulating materials allowed under the Canadian Home Insulation Program from 1976 to the mid-1980s. The CHIP program provided grants to homeowners to increase insulation levels, thereby reducing energy consumption. Instead of buying batts of insulation, homeowners could buy bags of loose vermiculite and pour them into wall cavities and between joists in the attic.
Similar to mica, if you discover these granules between the joists of your roof, it’s a safe bet to say that it is insulated with vermiculite. If your home was built before the 1990s, your vermiculite may contain amphibole asbestos fibers.
Vermiculite from the Libby mine in Montana, USA is known to contain high levels of amphibolic asbestos. Extracted from the mine between 1920 and 1990, this vermiculite insulation was sold in large bags mainly, but not exclusively, under the trademark Zonolite® Attic Insulation. The mine was closed in 1990. As well as being rich in vermiculite, this mine had the misfortune of having a deposit of tremolite, a type of asbestos. When the vermiculite was extracted, some tremolite came in with the mix.
For Canadian use, the raw product from the Libby mine was shipped to processing plants in Montreal, St. Thomas, Ajax and Toronto, and Grant Industries in western Canada. At these plants, it was processed and sold as Zonolite. In its good years, the Libby mine accounted for more than 70% of the world’s vermiculite production. The products from this mine have been used very little since the mid-1980s.
The main problem with the asbestos contained in vermiculite insulation is that its fibers are very friable and break off easily. At the slightest movement or agitation of the insulation, the light asbestos fibers are thrown in the air where they become likely to be breathed by the occupants. The severity of the effects of exposure to asbestos depends directly on the concentration and size of the fibers in the air, the duration and frequency of exposures and the time when the first exposure occurred. Inhaled in large quantities, asbestos fibers can cause the formation of scar tissue in the lungs which hinders breathing (asbestosis) and even lead to the development of lung cancer.
A good inspector should be able to identify the vermiculite, raise the alarm and strongly recommend proceeding with the analysis of a sample.
If the attic or walls of a house contain vermiculite insulation, leave it alone. Avoid disturbing the material. Do not sweep it or vacuum it up. Do not store belongings in the attic. If work is planned that involves these areas, for example installing pot lights in a room below the attic, send a sample of the vermiculite to a private lab. Send several samples, and use a lab specializing in asbestos analysis. If it is found to contain asbestos, or if you just assume it does, precautions should be taken. The safest approach would be to have the insulation in the affected areas removed by a qualified environmental contractor.
Should you need to remove the vermiculite insulation, the average cost to redo an entire attic (including removal of vermiculite and the installation of new insulation) is about $10,000.
