Learning that a home's siding contains asbestos can lead a homeowner to the conclusion that this siding must be removed immediately. The health risks of asbestos are well documented, and any homeowner is advised to exercise caution when it comes to a building material that contains asbestos.
But the reality of asbestos siding is different. Removing asbestos exterior siding can be more hazardous than leaving the siding in place. If left alone, asbestos-cement siding and other building products containing asbestos can be considered benign.
What Is Asbestos-Cement Siding?
Asbestos-cement siding is a thin type of siding shingle made from a mixture of Portland cement reinforced with asbestos fibers. The Portland cement binds asbestos fibers into a hard mass.
While asbestos is fireproof and can help limit or stop the spread of fire, asbestos was added to the cement as a binding agent to lend strength to the material. So, asbestos siding should be kept in place only because removing it is a health hazard, not because asbestos siding will fireproof your home.
Warning
When asbestos-containing materials are disturbed through sawing, sanding ripping, or demolition, the fibers become mobilized. This is when asbestos can pose a health risk if it is inhaled or otherwise ingested. If such materials are removed, extreme caution and special techniques are required, and the better strategy is usually to leave them in place or cover them up.
How to Identify Asbestos Siding
You can identify asbestos siding by a visual check or by having a laboratory test a sample.
- Asbestos-cement siding comes in many forms, but it often comes in shingle form and has low vertical grooves.
- Asbestos-cement siding is punctured around the perimeter in various spots with nails and each row is lapped over its lower, adjacent row.
- Broken asbestos-cement siding tiles are rough, flaky, and sharp along the broken edge.
- When you gently rap a suspected asbestos-cement siding tile, it will produce a sharp ringing sound similar to tapping on a ceramic tile.
- Check records transferred with the house sale that may identify the manufacturer of the siding or the date of installation.
- Send a sample of the siding to an approved laboratory for testing.
Asbestos Siding vs. Fiber-Cement Siding
Fiber-cement siding is a contemporary type of siding product that is widely used and bears a slight resemblance to asbestos siding. When fiber-cement siding is broken, it displays a ragged, fibrous edge, much like asbestos siding. Most fiber-cement siding contains no asbestos.
One-for-one asbestos siding shingle replacements made from fiber-cement contain no asbestos. It is recommended that you use this product to replace missing or broken asbestos shingles.
History of Asbestos-Cement Siding
Asbestos cement was first developed in 1905 by the Johns-Manville company, which became one of the premier manufacturers of cement-asbestos materials.
By 1910, home builders and homeowners could purchase Asbestoside, the trademarked name for a type of asbestos siding made by J-M Roofing. J-M was a shortened version of Johns-Manville.
Siding material and other products using asbestos-reinforced concrete continued to be sold and installed well into the early 1970s since it was believed that the process of making asbestos-cement encapsulated and neutralized the asbestos fibers.
This theory was later proven to be false, when it was demonstrated that asbestos-cement materials could also release asbestos fibers in their pure form when the materials were crushed, broken, or otherwise pulverized.
Asbestos-cement was not only commonly used but was a recommended siding material from the 1940s to the 1960s, due to its extremely durable and fireproof nature.
Pros and Cons
Fire-resistant
Resists insects and rotting
Textures simulate wood grain
Easy to clean and maintain
Less porous than wood
Chips and cracks easily
Damaged by pressure washer
Hazardous if broken
Replacements difficult to find
Should not be refurbished
Asbestos cement siding on a house should not necessarily be viewed as a serious problem. There are countless homes and garages with this siding material. When the siding is undisturbed and in good shape, the health hazards are minimal. The presence of asbestos-cement siding, in and of itself, is not a serious drawback.
Unlike more porous siding materials, such as wood clapboard, asbestos cement siding will not quickly soak up paint, which allows it to be painted more easily.
Asbestos-cement siding is very brittle and can be easily chipped, cracked, or broken. Even using a pressure washer for maintenance can crack the siding and lead to moisture intrusion if the pressure setting is high enough.
Asbestos cement can be dangerous if pulverized by sawing, sanding, or breaking. It can be difficult to find replacement asbestos-cement siding for repairs, with safe fiber-cement shingles being the best option.
Health Risks of Asbestos Siding
There is no question that asbestos fibers do pose a health risk, and this is the reason that building materials no longer include this material.
Asbestos is a naturally occurring silicate mineral that can be pulled into a fibrous material that is extremely resistant to heat and fire, and which has good insulating properties. Up until the early 1970s, asbestos was found in many building materials, thanks to these virtues.
The health risks of asbestos have been known for many years, since the early 1960s. Inhaled asbestos fibers have definitively been linked to a variety of lung diseases, including asbestosis and different types of cancer, such as mesothelioma.
No level of exposure to asbestos is deemed safe, although the people suffering from serious asbestos-related diseases are usually those who have handled the material regularly in jobs related to the manufacture and installation of asbestos and materials containing it. There are, however, documented instances of family members developing diseases simply by exposure to asbestos fibers carried home on the clothing of workers.
Removing Asbestos Siding
It's advisable to remove asbestos siding when doing major work on the house, such as building an addition. Have a certified asbestos abatement company do the work.
Removing asbestos cement siding is not a simple matter of calling up a local contractor. Begin by searching your state's Department of Environmental Quality for a list of licensed asbestos abatement contractors.
Depending on your locality, chances are good that you'll need to obtain special permits and have an asbestos abatement company perform the work. Such work can be done by a homeowner, but special procedures and disposal methods must be followed.
Alternatives to Removing Asbestos Siding
Despite some inherent advantages to asbestos-cement siding, and despite the inherent dangers of disturbing it through removal, some homeowners will want to remove it. Before undertaking removal, this should be carefully considered.
A safer strategy may be to cover it over with new siding, which effectively seals in the asbestos material. This is usually the preferred method of dealing with asbestos building materials.
Most siding companies are well-experienced in techniques for covering over existing asbestos-cement siding with new vinyl, aluminum, or fiber-cement siding. If a siding company removes an outer layer of siding and finds an older layer of asbestos-cement siding beneath, the standard procedure is simply to cover it over with new siding rather than remove it.
A home that has enclosed the old asbestos-cement siding with new siding is usually acceptable to home inspectors and real estate assessors, and it rarely has any negative effect on home values.
Asbestos-Cement Siding Basics
- Homes built between 1920 and the 1960s are likely to contain asbestos in any cementitious siding tiles.
- Cementitious siding installed after 1973 is very unlikely to contain asbestos. These materials are known as fiber-cement siding and they contain no asbestos.
- Cement-asbestos siding tiles do not need to be removed simply because they contain asbestos. There is no legal requirement to do so, nor is there a significant real estate value benefit.
- Avoid pressure washing asbestos siding, as this can crack the siding. Hitting the siding with a lawn mower can crack it, too.
Warning
Cutting, sanding, or breaking asbestos-cement tiles all pose a distinct health hazard. These actions release asbestos fibers into the air, and breathing or ingesting these fibers is dangerous. If you insist on removing the siding, hiring a company that specializes in asbestos abatement is strongly recommended.
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Is it safe to live in a house with asbestos siding?
It is generally safe to live in a house with asbestos siding as long as the siding is undisturbed. While it's safe to paint the siding, it should not be cut, drilled, or pried off.
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What is the best replacement for asbestos siding?
If asbestos siding is removed, it can be replaced with any type of siding of a similar thickness, such as vinyl siding or fiber-cement siding.
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What is the best way to cover asbestos siding?
The best siding to cover asbestos siding is a thin type of siding like vinyl siding. Thicker types of siding may push the siding beyond trim and other architectural details.
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Can you put vinyl siding on top of asbestos siding?
You can install vinyl siding on top of asbestos siding. Vinyl siding is one of the better choices for covering up asbestos siding because it is thin. Also, vinyl siding is expected to last 30 to 40 years.