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:
- It’s dangerous to enter your attic.
- It’s dangerous to perform a blower door test.
- It’s dangerous to perform any attic air sealing work until all of the vermiculite has been removed by a certified asbestos abatement contractor, at a cost ranging from $7,000 to $12,000.
- It’s dangerous to install cellulose insulation on top of the 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…