Asbestos Siding: Identification and Risk
Asbestos cement siding is durable and bound, which keeps it stable in place — and makes cutting, breaking, and power-washing the activities that matter.
Asbestos cement siding — sometimes called asbestos shingle or fiber cement siding — was manufactured by binding asbestos fibers into a hard cement matrix. That binding is the important fact about it: while the material is intact, the fibers are locked in place, and EPA states that asbestos-containing material in good condition that will not be disturbed will not release fibers. The risk arises from actions that break the matrix: cutting, sanding, snapping, drilling, or demolition.
Where asbestos siding came from
The EPA lists siding shingles and asbestos cement products among the materials that contained asbestos, alongside roofing shingles, ceiling and floor tiles, and pipe insulation. EPA ATSDR similarly identifies asbestos cement products as one of the principal building-material categories in which asbestos was used. ATSDR
The appeal for a cladding product is straightforward. Asbestos fibers are strong and heat resistant, ATSDR and adding them to cement produces a board that is rigid, fire-resistant, rot-proof, and cheap. As exterior cladding that has to survive weather and time, it performed well — which is why a great deal of it is still on buildings today, often still doing its job.
Why you cannot identify it by looking
The EPA states the constraint plainly: “Generally, you can’t tell whether a material contains asbestos simply by looking at it, unless it is labeled.” EPA
This applies to siding as much as to anything else. Asbestos cement board and later non-asbestos fiber cement board were made to serve the same purpose, in similar formats, and weather to a similar appearance. Age of the building narrows the question but does not answer it, and an unlabeled board cannot be resolved by inspection.
The EPA's guidance for resolving it is to have material sampled by a properly trained and accredited asbestos professional, who then uses a qualified laboratory to perform the analysis. EPA Our guide to testing for asbestos covers that process.
Bound material behaves differently
EPA’s position on undamaged material is equally direct: “Asbestos-containing material that is in good condition and will not be disturbed (by remodeling, for example) will not release asbestos fibers.” EPA
Asbestos cement sits at the non-friable end of the range: the fibers are held in a hard mineral matrix rather than loosely bound, so undisturbed siding on a wall is a very different proposition from deteriorating pipe lagging in a basement. ATSDR frames the general principle the same way — materials containing asbestos that are not disturbed or deteriorated do not, in general, pose a health risk and can be left alone. ATSDR
The activities that change the situation
ATSDR states that asbestos fibers may be released into the air by the disturbance of asbestos-containing material during product use, demolition work, building or home maintenance, repair and remodeling. ATSDR For exterior cladding, that maps onto a recognizable set of jobs.
- Cutting and drilling — fitting new windows, running a vent or cable through the wall, trimming boards to fit.
- Sanding and abrasive cleaning — surface preparation before repainting, or aggressive pressure washing, both of which abrade the surface of the board.
- Breaking and snapping — removal of individual damaged boards, where the material is brittle and tends to fracture.
- Demolition — the case OSHA identifies as generating the heaviest exposures.
OSHA notes that heavy exposures tend to occur in the construction industry and in ship repair, particularly during the removal of asbestos materials due to renovation, repairs, or demolition. OSHA
Deterioration over time
Cladding is weather-exposed by definition, and decades of freeze-thaw cycling, impact damage, and moisture take a toll. EPA's inspection guidance is triggered by exactly this condition: a home should be inspected by a trained professional if it has damaged building materials, or if remodeling is planned, since remodeling can disturb building materials. EPA
Conversely, EPA is explicit that testing is not always warranted: “If building materials in your home aren’t damaged and won’t be disturbed, you do not need to have your home tested for asbestos.” EPA
Repair and removal
EPA describes two categories of action available where asbestos-containing material is more than slightly damaged or could be disturbed, both to be carried out by trained and accredited asbestos professionals: repair and removal. EPA
Where action is needed, EPA states that “Removal is complex and must be done only by a trained and accredited asbestos professional. Improper removal may actually increase your and your family’s exposure to asbestos fibers.” EPA
That last sentence is the substantive warning for siding specifically, because exterior cladding looks like the most approachable of do-it-yourself jobs — accessible, outdoors, apparently well ventilated. Professional work is bounded by enforceable exposure limits: OSHA's construction standard sets a permissible exposure limit of 0.1 fiber per cubic centimeter of air as an eight-hour time-weighted average and an excursion limit of 1.0 fiber per cubic centimeter averaged over thirty minutes. OSHA 29 CFR 1926.1101 OSHA also states there is no safe level of asbestos exposure. OSHA
Common questions
Is asbestos siding dangerous to live with?
EPA states that “Asbestos-containing material that is in good condition and will not be disturbed (by remodeling, for example) will not release asbestos fibers.” EPA Asbestos cement binds its fibers into a hard matrix, so intact cladding is a different situation from cladding being cut or demolished.
Can I pressure-wash or sand asbestos siding before painting?
Abrasive cleaning and sanding break the surface of the board, which is the mechanism ATSDR identifies for releasing fibers from asbestos-containing material during maintenance, repair and remodeling. ATSDR EPA advises an inspection by a trained professional if you are planning to remodel, because remodeling can disturb building materials, or if the home has damaged building materials. EPA
Does asbestos siding have to be removed?
Federal guidance does not require removal on the basis of presence alone. EPA describes repair and removal as the two actions available where material is more than slightly damaged or could be disturbed, both to be carried out by trained and accredited asbestos professionals. EPA
Why the exposure question matters
The health concern attached to all of these materials is the same, and it is worth stating plainly rather than by implication. The EPA identifies three major conditions associated with asbestos exposure: lung cancer; mesothelioma, described as “a rare form of cancer that is found in the thin lining of the lung, chest and the abdomen and heart”; and asbestosis, “a serious progressive, long-term, non-cancer disease of the lungs.” EPA
ATSDR notes that the Department of Health and Human Services, the World Health Organization and the EPA have determined that asbestos is a human carcinogen, and that asbestos mainly affects the lungs and the membrane that surrounds them. ATSDR
Two features of these diseases shape how the risk is usually described. The first is delay: the EPA states that “Disease symptoms may take many years to develop following exposure,” EPA and ATSDR similarly notes that cancer from asbestos does not develop immediately but shows up after a number of years. ATSDR Our article on mesothelioma latency covers that interval in more detail, and what mesothelioma is covers the disease itself.
The second is the interaction with smoking. ATSDR states that cigarette smoke and asbestos together significantly increase the chances of getting lung cancer, and that for someone who has been exposed to asbestos, stopping smoking is the most important action they can take to improve their health and decrease their risk of cancer. ATSDR
This site is an informational resource and not a source of medical advice. Questions about personal exposure history or symptoms belong with a qualified clinician.
Key Takeaway
Asbestos cement siding binds its fibers into a hard matrix, and EPA states that asbestos-containing material in good condition that will not be disturbed will not release fibers. It cannot be identified by sight, and EPA advises sampling by a trained and accredited professional using a qualified laboratory. The activities that matter are the ones that break the matrix — cutting, sanding, pressure washing, snapping boards, and demolition — and EPA states that removal must be done only by a trained and accredited professional, because improper removal may increase exposure rather than reduce it.