Does Some Attic Insulation Contain Asbestos?

By: Bill Kibbel , Contributing Writer
In: Old House Inspection

I received an e-mail from a homeowner concerned that his attic might have asbestos insulation.  A home inspector pointed out that the insulation behind the upstairs knee-walls is called “something wool”.  It’s old, dirty and fibrous and the inspector told him that it should be tested for asbestos fibers.

Mineral Wool Insulation

“Rock wool” is made from mineral fibers manufactured from stone and waste from mining . It consists of aluminum silicate rock (basalt), furnace slag and limestone or dolomite.

Rock Wool

“Slag wool” is produced mainly from blast furnace slag with some natural stone.

The term for both types of this fibrous insulation is mineral wool.  Mineral wool was the most common thermal insulation for residential use until the 1960’s, when fiberglass insulation become the standard.  The raw materials are melted in furnaces and blown with air or steam over spinning drums or a centrifuge to create the fibers (picture making cotton candy).

Asbestos is a naturally occurring fiber that is mined.  Since mineral wool is a man-made fiber, it does not contain asbestos.  I’ve read about mineral wool, asbestos and resins mixed together to manufacture a couple specific industrial insulating products, but it’s not likely the kind of stuff used for residential insulation.

Other Insulation

“Balsam wool” is a shredded wood product, treated with borax as a fire-retardant.  It’s considered a very natural product and does not contain asbestos.

Balsam Wool

There is one type of  older insulation that has a significant possibility of being contaminated with asbestos.  That is the loose, granular insulation called vermiculite. See this article on vermiculite and asbestos for more information.

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

Other than vermiculite, it’s actually quite rare to find thermal insulation in residential attics that contains asbestos.  In those rare cases, the asbestos containing materials used for insulation were manufactured for some other purpose.  It was likely brought home from work at a factory or salvaged from some other type of building.  I heard one story of a worker at a ship-yard bringing the stuff home regularly and stuffing his attic full.


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  1. 32 Responses  to “Does Some Attic Insulation Contain Asbestos?”

  2. Adam
    Sep 12, 2016
    Hello, I helped with a refurb job in a 20-25 year old building last year. There were ceiling tiles (cellulose), then a space, and then layers of fibreglass insulation. I'm worried that the fibreglass insulation may have had some loose fill as well? Is this possible? I don't remember seeing anything loose fill but I don't really remember the event that much anyway, but it's really playing on my mind. What type of asbestos is in loose fill? When was it banned from use in the UK?
  3. Tom Kondra
    Dec 2, 2015
    I am preparing to sell my parents home which was built in 1949. The attic insulation installed is call Cellulite Cotton Insulation manufactured by The Gilman Brothers Company in Gilman, Connecticut. Does this insulation have asbestos in it? Thank you.
  4. Aurelia Weave
    Nov 9, 2015
    His house was built in the late 70's-early 80's; the garage has 4 panels of insulations (looks like previous owners took down several panels) called "Red Top insulation by US Gypsum. I need to know if this insulation has asbestos in it. Can you help me?
  5. Zargoosh
    Aug 28, 2015
    How can we use rockwool in fireproof powder production in a way that the rockwool wont stick together in mixing?
  6. Russell
    Aug 16, 2015
    Working on my grandparents place, in the attic there is a whitish product on top of the sheetrock ceiling kinda looks like ground up celotex.but also is fiberglass batt insulation on top of it, I live in south ga any ideas Thanks, Russell
  7. Ruben
    Jan 23, 2015
    I need to see a picture of an attic with new insulation. Can you send me one?
  8. Andre
    Oct 4, 2014
    I've been working on a home that has had water damage although the insulation has turned grayish and looks like gray pebbles but in this attic only in the attic.
  9. Sep 22, 2014
    I looked at a house recently and in the attic the insulation looked like little clay pebbles reddish orange in color. Also had 1" round disks in the mix. It looks like the field conditioner I use on my son's baseball infield for those that have this experience. The house is 100+ years old. Anyone have any idea what this may be? Thanks
  10. Dafi
    Aug 13, 2014
    I like to know more about how to produce slag wool in a laboratory scale for my pilot project. what equipment that i ned to produced slag wool? You can reply to my email : thank you
  11. Steve Delzell
    Nov 7, 2013
    I was inspecting a home built in the 1970s and discovered insulation in the attic that appeared to be similar to fiberglass but was completely black in color. Not just like mold or mildew but completely black. It had paper on one side but has been installed between the ceiling joists backwards with the paper towards the attic. There is also a fireplace in the home which is now gas burning, but I don't imagine that that much discoloration could be be from that. I was wondering if anybody else has ever seen this type of insulation before. Is there rolled rockwool that was made it was completely black and color?