Glossary · Insulation & windows
Vermiculite insulation (Zonolite)
Also called: vermiculite · Zonolite Attic Insulation · vermiculite attic insulation
A pebbly, brownish or silvery loose-fill attic insulation that may contain asbestos from a Montana mine, so it shouldn't be disturbed.
What it means
Vermiculite looks like small, light, accordion-shaped pebbles. Much of the vermiculite sold until 1990 came from a mine near Libby, Montana, whose ore was contaminated with asbestos, and it was often sold as Zonolite. Health agencies say to assume it contains asbestos, leave it undisturbed, keep people and storage out of the attic and hire trained professionals before any work there.
Why it matters in an audit
Finding vermiculite changes the plan: attic air sealing and insulation shouldn't go ahead until it's assessed and, if needed, removed by professionals.
Typical numbers
Reference values with their sources. Your auditor’s report gives the figure for your own house.
| What | Value | Source |
|---|---|---|
| US supply (EPA) | The Libby mine supplied over 70% of US vermiculite from 1919 to 1990 | epa.gov ↗ |
| Insulating value (NRCan) | About R-2.1 to R-2.3 per inch | natural-resources.canada.ca ↗ |
In the United States
EPA says to assume vermiculite contains asbestos and not to remove it yourself; testing can be costly and may give unreliable results.