Vermiculite / Zonolite Insulation discovered…now what?


Vermiculite does have its dangers…

R ecently while conducting a home inspection in Amherstburg I came across a property that had vermiculite as insulation. Upon first sight, it seems quite alarming. I remembered my training and undisturbed vermiculite is non harmful. For those who are unaware of what vermiculite actually is I've included an article supplied by my report writing software and notarized leader of the inspection industry Carson Dunlop (see "Vermiculite Insulation" below).

Basically, vermiculite is a rock type substance that was utilized in the 70’s as an insulating agent. It was poured into attics by the bag and acted as an insulator and also proved to be fire retardant. Some of the insulator contained particles of asbestos mined out of Quebec mines. This is where the difficulty lies. Obviously, the problem is the safety factor in having this substance in your home. Do you purchase a home that has vermiculite in the attic? My answer: be thorough. Be thorough in your investigation in regards to the asbestos content in the material. Vermiculite can have asbestos or it may have no content at all. This is why it is imperative, upon discovery, to have samples tested.

Binder Home Inspections does not recommend local I.D. and removal companies but, the services do exist. The company will enter the attic space and take 3 or 4 bagged samples and have the samples tested. Some companies have the samples tested locally whereas other companies send the samples out of town for verification. Once the material has been identified as not harmful, it is alright for the Owner/Buyer to remove the substance and insulate.

Do you remove the substance or do you insulate over the vermiculite. This is a personal choice. After the substance is deemed safe, I would (personally) still remove the rock. Let’s start fresh, get rid of the substance and give your attic a new coating. If you decide to blow in insulation, have it spray foamed, or roll fiberglass…a new layer should be applied. If you are the Seller and decide to keep the material in the attic, please keep the negative test results. This will make for easier identification for the Home Inspector, and ease the mind of the potential Buyer. As a certified Inspector I will not spend any time in an attic that has vermiculite. I will re-evaluate once the substance has been negatively identified and continue with the attic inspection. Please read the following article from Carson Dunlop in regards to this issue.

If you have any questions or comments regarding this topic please call Binder Home Inspections @ 519-995-2067 or e-mail your questions to



What Is It?

If you have never seen vermiculite insulating an attic, you may have seen it in potting soil. Vermiculite is a naturally occurring mineral worldwide. When heated rapidly to high temperatures, this crystalline mineral expands into low density, accordion-like, golden brown strands. In fact, its worm-like shape is what gives vermiculite its name. The worms are broken into rectangular chunks about the size of the eraser on the end of a pencil. In addition to being light, vermiculite chunks are also absorbent and fire retardant. These characteristics make it great as an additive, for example to potting soil. It also makes a good insulating material.

Where Was It Used?

Sold under various brand names, such as Zonolite Attic Insulation, the insulation came in big bags. Thousands of homeowners simply opened the bags and poured the vermiculite onto their attic floor and sometimes down exterior walls. It was generally not used in new construction.

When Was It Used?

Worldwide, vermiculite has been used in various industries as long ago as 1920. With the upsurge in home ownership during the baby boom, vermiculite insulation was a popular material in the 1950’s, and continued with the energy crisis into the late 1970’s. In Canada, it was one of the insulating materials allowed under the Canadian Home Insulation Program from about 1976 to the mid-1980’s. The CHIP program provided grants to homeowners to increase insulation levels, reducing energy consumption.

What Is The Problem?

The majority of the vermiculite used worldwide was from a mine in Libby, Montana, owned and operated since 1963 by W.R. Grace. 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 Grace subsidiary F. Hyde 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.

What Is The Risk?

Asbestos minerals tend to separate into microscopic particles that become airborne and are easily inhaled. People exposed to asbestos in the workplace have developed several types of life-threatening diseases, including lung cancer. Workers in and around the Libby mine developed serious health problems.

Like any hazards, length and intensity of exposure are major factors in the risk of asbestos-related respiratory illness. To assess the risk of asbestos exposure at a house, a sample of the vermiculite would need to be analyzed by a lab. Since most of the vermiculite used in Canada was taken from the Libby mine, the odds are quite good that there is asbestos in the vermiculite in Canadian attics.

The good news is that we don’t live in our attics. In addition, as long as it is undisturbed, neither the asbestos fibers bound up in the vermiculite chunks nor the dust will be released into the air. According to the National Institute for Occupational Safety and Health in the U.S., “Most people who get asbestos-related diseases have been exposed to high levels of asbestos for a long time.” Lastly, most of the time the air in your house flows from the house into the attic, rather than into the house from the attic.

The bottom line is, like most household products that may contain asbestos, and there are many, doing nothing is often the best approach. Naturally, the risk of exposure increases with the amount of time spent in the attic.


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 potlights 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.

For smaller jobs it may be sufficient to isolate work areas with temporary barriers or enclosures to avoid spreading fibers, use disposable protective clothing, and use proper respiratory protection. An important note – disposable respirators or dust masks are not appropriate for asbestos. Again, it is best to consult a qualified contractor.

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No text or graphical material may be copied from this site without the express written permission of Carson, Dunlop & Associates Ltd. Line drawings are from the Carson Dunlop Home Inspection Training Program and Home Inspection Software Tool – Horizon

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