I obtained an e-mail native a homeowner pertained to that his attic could have asbestos insulation. A home inspector mentioned that the insulation behind the maximum floor knee-walls is called “something wool”. It’s old, dirty and fibrous and also the inspector called him that it must be tested for asbestos fibers.

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Mineral wool Insulation

“Rock wool” is do from mineral fibers made from stone and waste indigenous mining . It is composed of aluminum silicate rock (basalt), heater slag and also limestone or dolomite.


“Slag wool” is created mainly from blast furnace slag through some organic stone.

The term because that both types of this fibrous insulation is mineral wool. Mineral wool to be the most common thermal insulation because that residential use till the 1960’s, as soon as fiberglass insulation come to be the standard. The raw materials are melted in furnaces and blown v air or steam over spinning drums or a centrifuge to produce the yarn (picture making cotton candy).

Asbestos is a naturally emerging fiber the is mined. Because mineral structure is a fabricated fiber, it does not contain asbestos. I’ve read about mineral wool, asbestos and resins blended together to manufacture a couple specific industrial insulating products, however it’s not likely the type of stuff supplied for residential insulation.

Other Insulation

“Balsam wool” is a shredded hardwood product, treated v borax as a fire-retardant. It’s considered a very natural product and does no contain asbestos.


There is one form of enlarge insulation that has actually a significant possibility of being contaminated through asbestos. That is the loose, granular insulation called vermiculite. See this article on vermiculite and asbestos for much more information.

Fiberglass and cellulose room the most common insulation mounted in residential attics today. I have never read or heard of either containing any kind of asbestos fibers.

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Other than vermiculite, that actually quite rare to uncover thermal insulation in residential attics that includes asbestos. In those rarely cases, the asbestos containing products used for insulation were manufactured for some other purpose. It to be likely lugged home from occupational at a manufacturing facility or salvaged from part other kind of building. Ns heard one story of a worker in ~ a ship-yard bringing the stuff home regularly and also stuffing his attic full.