Dear Bill,

I have a circa 1932 upscale home. It has asbestos shingles on a 4:12 pitch (probably cement asbestos combed shingles). The roofing is covered with lichens, mold, and pollution.

The condition of the shingles, as far as I can see, is fair-to-good. The nail ends exposed in the attic show no discoloration or water stain rings. I don't want to re-roof if there is a safe way to clean this roof without damaging the surface and without invoking EPA regulations.

Do you have any suggestions?


Dear Joe,

The dangers of asbestos (which was the hysteria of the 1980's similar to what "mold" has become today) are very often overblown. Residential products that contain(ed) asbestos include:

  • Radiant heat boiler and pipe insulation
  • Sprayed acoustical (cottage cheese) ceiling treatment
  • Drywall joint compounds and patching plaster
  • Acoustical ceiling tiles
  • Wooden fuse boxes
  • Wood stove fire-retardant floor and wall panels
  • Some linoleum and vinyl floor tiles
  • Insulation on knob and tube electrical wiring
  • Vermiculite attic and wall insulation
  • Heating duct insulation
  • Roofing felt or tar paper, and
  • Combed cement asbestos shingles used as roofing and siding in the 1930's to 50's.

Although asbestos was generally banned from construction materials in 1978, even today, some products still include asbestos, such as Transite gas flue pipe, artificial ashes, concrete gas logs, and wood stove door gaskets.

Unless asbestos fibers are "friable" -- which means that it can be crushed into a powder -- it presents no hazard whatsoever. Asbestos is dangerous only when it is breathed into the lungs. Therefore, products that are not friable are not dangerous.

Unlike sprayed acoustical ceilings and drywall joint compounds, (which are often scraped and sanded into dust) products like vinyl floor tile and cement asbestos shingles are very stable. That's why, after more than 70 years, the roofing material you are concerned with is still serviceable -- even though it is not very attractive.

It is my judgment that cleaning these shingles with a high-pressure wash should make them presentable. It is highly unlikely that this treatment would cause any of the asbestos fibers locked in the cement shingles to become airborne.

A reasonable assessment of the dangers of asbestos products was addressed by the American Medical Association in a report issued in 1991. The AMA recommended that, rather than remove asbestos containing products, they be encased wherever possible because removing them created more danger of airborne fibers.

That means, (that regardless of the hyperbole you might have seen about this topic on TV programs like This Old House) if you have a sprayed-on cottage cheese ceiling installed before 1978 it is best to simply put another layer of drywall ceiling over it. Or if you have a circa 1930's forced air furnace with asbestos duct insulation, it is better to incase the ducts with new insulation rather than try to remove it.

1 Sources:

Harvard University symposium report - "Exposure to Asbestos in Buildings"

Science Magazine, 1991, "Asbestos: Scientific Developments and Implications for Public Policy"

Journal of the American Medical Association, 1991, "Managing Asbestos"

A 1991 news release by the Safe Building Alliance, Washington, D.C.

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