How to Identify Dangerous Asbestos Insulation

Damaged floor tiles

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Asbestos hardly needs an introduction anymore. By now, most homeowners should be schooled in the general dangers of disturbing and breathing asbestos fibers. In older homes, specifically, asbestos may be found in products ranging from furnace and hot water pipe insulation to floor tiles. The recommendation is usually to leave it in place and not disturb it, if at all possible, or to have a professional asbestos abatement company handle it when removal is unavoidable. But asbestos can also be found in some types of loose-fill attic and wall insulation, too. You have no worries if your insulation is in batt form—the type of insulation that may pose a risk is ​loose-fill insulation that is poured loosely into joist or wall stud cavities. Beneath attic floorboards or inside walls, you may find many thousands of loose particles. That's the type of insulation that could pose a risk. 

How, exactly, can you identify whether your attic insulation is asbestos? Let's look at the particulars of loose-fill insulation that may contain asbestos. 

Vermiculite Attic Insulation

The main source of asbestos danger concerns vermiculite attic insulation, but not all brands or all sources of vermiculate pose a hazard. There is nothing inherently bad about vermiculite, which is a pellet-like mineral that expands at high temperatures and which is often used for gardening as an amendment that loosens soil and improves its ability to transmit water. 

Vermiculite is also used for insulation, in particular, the vermiculite that was mined by the Libby company in Montana for about 70 years, under the brand name Zonolite.

Zonolite presents a health danger only because it was contaminated with tremolite, an asbestos-like mineral. Even though the majority of U.S. vermiculite attic insulation did come from the Libby mine, keep in mind that about 30% did not come from this source.

Your Loose-Fill Insulation May Contain Asbestos If:

  • Your house was built before 1990. Because the Libby mine closed in 1990, houses built or remodeled before that date might have asbestos-containing attic insulation. If it was built after 1990, the chances are reduced but not eliminated.
  • The insulation particles have a certain color. Zonolite is usually gray-brown or silver-gold.
  • The particles have an accordion-like texture. Because Zonolite is subjected to heat, the accordion texture is a result of the particle puffing up.
  • If the insulation lays flat: Zonolite lays flat and firm in the joist cavity, as opposed to loose-fill fiberglass, which tends to fluff up, much like a snow drift.

Although Zonolite is a mineral, it is lightweight, because during the production process it is subjected to high heat that causes the particles to puff up.

Is the Loose-fill Gray, Soft and Without a Shine?

If so, it is probably cellulose insulation. Cellulose has a high recycled paper content, no minerals. Close examination will show that this puffy gray material does not contain earth minerals at all, but will look like shredded gray paper. Cellulose insulation is a perfectly safe type of insulation that is blown into the cavities between the joists. 

Is the Loose-fill White and Fluffy, With a Little Shine?

If so, it is probably fiberglass fill. Because it is a glass product, fiberglass will have a slight shine when subjected to bright light. It is very soft, almost like cotton candy. Fiberglass can be a breathing nuisance, but it is not known to cause cancer.

Is the Loose-fill Gray, Puffy, and Fibrous?

Another mineral-based loose fill insulation is rock wool, which frequently appears as bundles of fibers with a soft, cottony appearance. Rock wool is white, off-white or brownish-white. Rock wool is a manufactured product, made by melting basaltic rock and dolomite and adding binders. The raw material is heated to 2,750 degrees Fahrenheit until it melts. The molten material is spun into fibers with air pressure. Rock wool is installed as loose insulation or as woven insulation batts, and like fiberglass, the insulation fibers should be handled with care, but are not known to cause cancer. 

illustration of attic insulation types
Illustration: Elnora Turner. © The Spruce, 2019 

What if I Suspect I Have Zonolite Vermiculite Insulation?

If your loose-fill insulation fits the visual cues for vermiculite insulation, you can check to see if it is the asbestos-carrying Zonolite type by purchasing a DIY asbestos testing kit or seeking a commercial firm who can test for asbestos. DIY kits are usually available for less than $50. If you discover that you do have insulation containing asbestos, you are well advised to seek an abatement company to handle its removal. Unfortunately, this is an expensive proposition, but you cannot place a price on your family's health.