Can I Install Insulation Over Vermiculite?

by Erik North on May 8, 2012

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I often say my blog is about answering common customer questions, and in any home where we discover vermiculite, the customer asks whether you can just blow insulation over it. I was thinking of just writing ‘No’ for this entry and calling it a day. Maybe I could send it to Guinness to see if it’d be the shortest blog post ever.

In Maine, there’s an awful lot of vermiculite insulation. I’ve heard (very likely apocryphal) stories, claiming that barrels of the stuff were ‘borrowed’ from local shipyards and construction sites to re-purpose as home insulation. Maybe folks will return it when they’re finished.

Vermiculite as Insulation

Vermiculite was in the heady, pre-lawsuit days, one of the more commonly used insulations. In it’s day, vermiculite was installed in thousands and thousands of homes. As the dangers of asbestos exposure become more well known, vermiculite came under close scrutiny.

Then it was discovered that one of the most prominent vermiculite mines in Libby, Montana, had elevated levels of asbestos. Hooray. Vermiculite has since been phased out of use as a residential attic insulation.

I’m not going into too much detail about vermiculite here. For more details, here’s my pages on vermiculite and Zonolite brand vermiculite:

Post on Vermiculite
Post on Zonolite brand Vermiculite

What is Vermiculite

Vermiculite is a shiny gray brown fibrous mineral. When heated, moisture trapped in the fibers steams out, puffing the vermiculite to several times its original size. It is fireproof, water resistant and a good sound retardant and insulator. Far from all vermiculite contains asbestos. However, because of its possible presence and the widespread use of Libby mine vermiculite, it has been associated with asbestos and asbestos-related illnesses.

Adding Insulation Over Vermiculite

Which gets us back to adding insulation. The concern is with the possibility of asbestos. Applying insulation, be it blowing loose fill fiberglass/cellulose or laying down batts, is messy and very dusty work. Jostling the vermiculite can cause any loose fibers to become airborne. Inhalation of asbestos fibers can be a severe health hazard.

The presence of vermiculite can be an impediment to energy audits, weatherization and insulation work. One of the most important energy auditor tools is the blower door. This tremendously powerful fan can easily disturb loose asbestos fibers.

A responsible audit requires a full visual inspection of the entire property (searching for loose vermiculite and asbestos) prior to running the blower door. Similarly insulation and weatherization work must either be preceded by full asbestos abatement.

Homeowners may not like it but this is a very clear cut situation. If they want to add insulation, an abatement pro ought to be brought in to first test, and if necessary, remove the vermiculite.

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