If you’re under the impression that natural insulation materials are the safest ones to use, it might be time to think again. Vermiculite is a natural insulation material — but it’s one that you definitely don’t want to have in your attic.
Vermiculite is a mineral mined from the earth, composed of shiny flakes that look like mica. When this mineral is put in an oven, it expands like popcorn. Expanded vermiculite is lightweight, fire-resistant, and odorless; since it has an R-value of about R-2 per inch, it was used for decades as an insulation material.
There is only one problem with this wonderful material: most vermiculite contains friable asbestos. When inhaled, vermiculite dust can cause cancer.
Owners of homes with vermiculite have a huge headache. If your attic contains vermiculite:
That’s why it’s so much better to have an attic with no insulation at all than it is to have an attic with 8 inches of vermiculite.
If an attic is insulated with a thin layer of vermiculite — a layer that provides less than the minimum R-value required by code — it’s hard to come up with a good way to improve the insulation layer, especially if the ceiling has air leaks. Addressing attics with vermiculite is a particular challenge for weatherization agencies.
Where does it come from?
Vermiculite insulation was sold in the U.S. from 1919 to 1990. More than 70% of U.S. vermiculite came from a single mine near Libby, Montana. Vermiculite insulation was sold in bags to builders and homeowners under the Zonolite brand name. Founded in 1919, the Zonolite company was acquired by W.R. Grace Company in 1963.
According to a 1985 estimate made by the Environmental Protection Agency (EPA), about 940,000 American homes were insulated with Zonolite.