What You Should Know About Asbestos Siding

Asbestos siding, also sometimes referred to as asbestos shingles or transite siding, was a popular exterior wall material used on many buildings in the 20th century. However, in recent decades it has become widely known that asbestos exposure can cause serious health issues, leading asbestos siding to be mostly phased out of use.

If you live in an older home that contains asbestos siding, it’s important to understand the potential risks as well as the options for safely managing it. Here is a thorough guide on what you should know about asbestos siding.

What is Asbestos Siding?

Asbestos siding, or asbestos cement siding, is a composite building material consisting of Portland cement reinforced with asbestos fibers. Unlike natural siding materials like wood clapboard or stone, asbestos siding is a manufactured product.

The asbestos fibers provide strength and durability while also allowing the material to be molded into different shapes. Asbestos cement siding was sold in shingles, planks, or sheets and was used as an exterior wall covering for many types of buildings.

The primary producers of asbestos siding in the United States were Johns Manville and CertainTeed. It was especially popular in the post-World War II residential construction boom from 1945 to the 1970s.

The material was prized for being affordable, fireproof, and low-maintenance. The cement provided durability while the asbestos fibers gave it strength and flexibility. Asbestos siding is resistant to rot, insects, and acid rain.

Unlike wood, it didn’t require periodic repainting. It was also easy to install. For these reasons, asbestos siding was seen as a wonder product and used on millions of American houses, schools, commercial buildings, and industrial facilities during the 20th century. The peak years of installation were between 1945 and 1972.

Why is Asbestos Dangerous?

Asbestos refers to a naturally occurring group of silicate minerals made up of microscopic fibers. There are several types, but the most common ones used commercially are chrysotile, amosite, and crocidolite.

The very qualities that made asbestos so versatile and cost-effective – its strength, durability, heat resistance, and flexibility – also make it hazardous to human health.

Asbestos fibers are easily released into the air when disturbed. When inhaled, the thin fibers become lodged in lung tissue and abdominal cavities. The body cannot break down or remove the fibers, leading to irreversible scarring that causes asbestosis and other diseases.

The adverse health effects of asbestos exposure have been definitively proven to include:

Asbestosis – scarring of lung tissue that makes breathing difficult
Lung cancer – asbestos is a known carcinogen
Mesothelioma – an aggressive cancer affecting the membranes around major organs
Pleural thickening – buildup of scar tissue around the lungs

Symptoms of these diseases may take 10-50 years to manifest after exposure. This long latency period means harm can continue long after use of the material has ended.

There is no safe threshold of asbestos exposure. According to the Occupational Safety and Health Administration (OSHA), any detectable concentration is considered hazardous.

This is why asbestos-containing buildings must be handled with care and worked on only by licensed abatement professionals. Improper disturbance can release fibers into the air, posing a danger to inhabitants.

When Was Asbestos Siding Used?

Asbestos cement building products were first manufactured in the early 1900s. Their popularity increased throughout the mid-20th century due to asbestos’ fire resistance and affordability. Some key historical points:

Early 1900s – Asbestos cement patented in Austria. Johns Manville and CertainTeed begin producing it commercially in the U.S.
1920s – Asbestos shingles introduced as affordable roofing material
1930s – Asbestos siding production expands greatly as exterior wall option
1940s – Use increases after WWII, peaks in 1950s and 60s
1970s – Health risks confirmed, U.S. phases out use
1989 – All new asbestos products banned in U.S. under TSCA

Although new applications were banned starting in the 1970s, existing asbestos siding could legally remain in place. Buildings constructed through the early 1990s could still contain it.

It continues to deteriorate and pose hazards today. Any structure dating from the early-to-mid 20th century that has not been abated should be presumed to contain asbestos. Testing is the only way to know for sure.

Types of Asbestos Siding

There are three main types of asbestos siding that were manufactured as exterior building materials:

1. Asbestos Shingles

Asbestos shingles are flat, asphalt-impregnated sheets made of asbestos and cement. They were one of the earliest forms of asbestos siding, used as a cladding material for exterior walls and roofs.

Shingles were mass produced in the 1920s and saw heavy use over the following decades. They came in solid or perforated sheets around 12 x 24 inches in size with a shingle-style profile. Shingles were nailed in overlapping rows to form a pattern across walls or roofs.

This siding contains 15-20% asbestos fibers. It was often painted or coated for appearance. Asbestos shingles are one of the most recognizable forms of siding seen on mid-century buildings.

2. Asbestos Planks/Boards

Like shingles, asbestos cement planks contain 15-20% asbestos fibers. These boards were manufactured in smooth 4 x 12 feet sheets ranging from 1/8 to 5/16 inches thick.

Planks allowed for faster installation compared to individual shingles. The boards were cut to size and screwed horizontally across a building’s exterior walls. They have a more modern, streamlined look compared to the shingled pattern.

Asbestos planks were especially popular for industrial buildings, public housing projects, schools, and commercial structures from the 1950s through the 1970s.

3. Asbestos Lap Siding

Lap siding refers to wide, beveled boards designed to overlap horizontally with hidden fasteners. This gives walls a seamless appearance. Asbestos cement versions were produced in widths ranging from 6 to 12 inches.

Lap siding was commonly seen on residential and commercial buildings needing a more attractive, finished exterior look compared to shingles. It was often painted.

In addition to these main siding types, asbestos cement was also used for soffits, vertical siding, and miscellaneous wall panels. Any form of rigid asbestos board nailed to an exterior wall falls under “asbestos siding”.

How to Identify Asbestos Siding

If you suspect your building has asbestos siding, the only way to confirm is through laboratory testing. However, there are some telltale signs that point to its likelihood:

Age – Homes or buildings constructed between 1930-1980 often contain it
Color – Gray, tan, or dark brown panels
Surface – Flat or textured boards rather than wooden planks
Labels – Vintage siding boxes or material stamps
Location – Widespread east of the Rocky Mountains

The brands Johns Manville and CertainTeed were the major producers. Look for their logos or the initials “JM” stamped onto boards. These are clues the siding contains asbestos.

Homes with asbestos siding will also lack the horizontal lines of traditional wood siding. Up close, fibers may be visible at cracked or broken edges.

There is no definitive way to identify it visually. The only way to know for sure is to take a small sample and send to an accredited lab for analysis. Most building inspectors or environmental consultants can perform this testing.

Asbestos Siding Health Risks

The known health risks of asbestos exposure are primarily associated with inhaling fibers. Asbestos siding poses a few potential hazards:

Fibers released when damaged – Normal weathering, hail, lawn equipment hitting walls, etc. can release fibers at impact points. This is more likely with older, deteriorating boards.
Fibers released during removal – Any work performed on the siding can disturb it and discharge fibers into the air if proper precautions aren’t followed. The EPA does not recommend do-it-yourself removal.
Indoor contamination – Asbestos fibers tracked indoors can accumulate in dust, posing a hazard if inhaled. Proper sealing is important.
Soil contamination – Over time, released fibers can build up in the surrounding soil. This shouldn’t affect ambient air quality but may require remediation if the property is redeveloped.

For these reasons, asbestos siding should be sealed, maintained, and/or removed by qualified professionals. Residents and neighbors should follow best practices to minimize potential exposure.

Is Asbestos Siding Dangerous if Left Untouched?

Intact, sealed asbestos siding that is not being actively disturbed poses close to zero risk. The mere presence of the material does not make a building unsafe.

The danger arises when the brittle cement boards become damaged, cracked, or eroded to the point where asbestos fibers are released. Damage can come from:

Direct mechanical impact – Lawnmowers, debris, etc. striking walls
Weathering deterioration – Freezing, hail, moisture causing boards to delaminate over time
Vibrations – Traffic, heavy equipment operating nearby
Damage from adjacent work – Re-siding, window replacement, etc. if improperly done

If the siding remains sealed and in good condition, it generally does not pose a health risk. There is no need to remove it unless active repairs or demolition are planned. It can usually remain until a building is slated for major renovations or redevelopment.

Is Painting or Sealing Asbestos Siding Recommended?

Applying protective coatings is an effective way to encapsulate asbestos siding and minimize deterioration. This prevents hazardous fiber release. According to the U.S. Department of Health, sealing materials is preferable to removing undamaged asbestos.

Painting or sealing intact siding can extend its usable lifespan. Recommended methods include:

High-quality exterior grade paint – Provides a protective barrier and improves appearance. Can delay the need for replacement. Should be reapplied periodically.
Penetrating sealants – Sealants soak into porous cement material for weatherproofing. Helps prevent cracking and delamination. Provides long-lasting encapsulation when properly applied.
Thick coatings – Acrylic, epoxy, or urethane products can totally seal the surface. This offers maximum protection but modifies the appearance substantially.
Vegetation – Growing vines or bushes directly on walls covers siding and prevents damage. Provides a living barrier.

Sealing asbestos siding comes with some precautions:

Only intact, non-friable siding should be coated. Severely damaged areas must be removed first.
Proper protective equipment like respirators and full coveralls must be used during sealing work. Surfaces should be lightly wetted first to keep fibers down.
Coatings must be reapplied on a regular basis to maintain protection as they wear down over time.

Sealing alone should not be relied on forever, but it can significantly extend an asbestos siding lifespan 10-20 years or more. This minimizes risks until a planned overhaul.

Asbestos Siding Removal: Should You Remove It?

Simply having asbestos siding does not necessitate removal. Since risks arise when asbestos-containing materials degrade, keeping siding well-maintained and undisturbed is often the safest option.

However, there are some circumstances when removal is advisable:

Renovation or demolition – Any projects that significantly impact exterior walls require asbestos removal first. This is mandated by OSHA and EPA regulations.
Extensive damage – If boards are severely delaminated, cracked, or eroded, it’s better to remove than try encapsulating.
Prior to re-siding – New siding cannot be installed over asbestos siding.
Peace of mind – Some property owners prefer complete removal for personal reasons.

Removal is always recommended before major renovation or demolition. Otherwise, it’s often prudent to leave undisturbed asbestos siding intact and simply maintain good seals and coatings.

Asbestos Siding Removal Process

Removing asbestos siding requires extensive containment preparations and rigorous protocols to keep work areas sealed off and avoid fiber release:

Abatement plan – A licensed asbestos surveyor creates a detailed plan for the job, including staging areas, negative air systems, waste handling, etc.
Permits – Removal must be permitted based on jurisdiction. Notification and air monitoring are usually required.
Containing work zones – The building exterior is completely sealed in plastic sheeting with a decontamination chamber at entrance and exit points to avoid spreading fibers.
Negative air pressure – HEPA filtered negative air machines keep air pressure lower inside containment compared to outside. This ensures fibers cannot escape.
Personal protective equipment (PPE) – Workers wear respirators, full decontamination suits, gloves, and foot coverings.
Wet removal methods – Siding is continually soaked during removal to keep fibers down. Material is immediately bagged.
Air testing – Phase contrast microscopy (PCM) air sampling is conducted daily to ensure no fibers escape containment.
Waste disposal – Asbestos siding must be disposed of as hazardous waste in specially permitted facilities.

Removal is extremely labor intensive and complex. Improper containment or hasty work can release hazardous fibers. It should only be done by licensed asbestos abatement professionals.

Asbestos Siding Replacement: What to Use Instead?

Once asbestos siding has been safely removed, a building will require a new exterior wall covering. There are several modern materials that make good alternatives:

Vinyl siding – Economical, low maintenance, and mimics a painted wood look. Widely used for homes. Has improved impact resistance compared to older vinyl.
Fiber cement boards – Durable like asbestos but without the safety issues. Can be painted. Withstands weather very well.
Composite boards – Made of plastic and wood fibers. Hold paint very well. Withstand impacts. Good longevity.
Wood boards – Traditional appeal, but requires painting/staining. Oak, cedar, and redwood have good weather resistance.
Stucco – Attractive plaster finish. Used often in southwestern regions. Periodic cracks need repairing.
Brick or stone veneers – Mimic structural masonry at a lighter weight. Expensive but extremely durable and attractive finish option.

Modern building codes may dictate minimum insulation values, wind load resistance, and other parameters that factor into replacement siding selection. An architect can recommend the best options tailored to a specific property.

Maintaining and Monitoring Asbestos Siding

For buildings where asbestos siding remains in place, diligent maintenance and monitoring are crucial:

Inspections – A certified asbestos inspector should examine all surfaces at least annually. This identifies any new damage.
Seal any cracks – Small fractures or holes can be filled with asbestos-rated caulk. Larger areas may need professional patching.
Reapply coatings – Paints or penetrating sealants deteriorate over time. Reapply as needed to keep siding fully encapsulated.
Avoid contact – Prevent damage during lawn care, painting, pruning trees, etc. Consider soft landscaping around walls.
Monitor before/after storms – Hail or debris impact can damage siding. Inspect and address promptly.
Consider partial removal – Removing the worst sections may be worthwhile rather than maintaining indefinitely.
Keep interior clean – Wet wipe and HEPA vacuum interior spaces near damaged areas to remove any tracked-in fibers.

Damaged asbestos siding must never be sanded, sawed, or aggressively scraped during maintenance. Always use proper PPE and wet methods.

Asbestos Siding: Necessary Precautions for Homeowners

Living in a home with asbestos siding does not necessarily mean harmful exposure will occur. But precautions keep risks minimal:

Learn the location of all asbestos materials and inspect regularly for new damage.
Avoid unnecessary contact with siding. Keep landscaping at least 2 feet away.
When doing exterior work, follow safety protocols or hire licensed asbestos professionals.
Use high-quality paint and sealants to encapsulate existing siding.
Prevent indoor dust buildup. Wet wipe surfaces and deep clean carpeting.
Remove shoes before entering to avoid tracking in outdoor contaminated dirt.
Keep household members informed. Exercise extra caution with children.
Develop a long-term abatement plan. Seek qualified contractors, not the cheapest option.

Asbestos exposure risks come primarily from inhaling fibers. With proper precautions, asbestos siding can often remain in place without causing harm.

Removing Asbestos Siding DIY: Is It Ever a Good Idea?

It’s understandable why homeowners want to consider do-it-yourself asbestos projects to save on removal costs. However, asbestos work is complex and dangerous.

Improper handling can endanger yourself and your family and is also illegal. Fines of up to $70,000 per day can be charged for non-compliant removal work.

There are no safe “shortcuts” when it comes to asbestos. It would be unwise to attempt any kind of DIY removal except under very specific circumstances:

Only for small-scale repairs of minor areas, not whole walls
Using extensive personal protections and wet removal methods
No power tools allowed; hand tools only
Following all disposal regulations
Ensuring no fibers are released

Realistically, DIY removal is never advisable.