Roofing Asbestos
Roofing asbestos encompasses a broad range of weather-resistant, non-combustible building materials widely installed on residential dwellings and commercial industrial complexes between 1900 and the mid-1980s. Valued for its extraordinary fireproofing and imperviousness to weathering, asbestos was incorporated into corrugated transite cement roof panels, asphalt shingles, underlayment felts, and black flashing mastics.
Types and Historical Applications of Asbestos Roofing Materials
During the twentieth century, commercial and residential roof systems required heavy fire resistance to prevent embers from igniting roof decks. Manufacturers formulated various roofing components using chrysotile and crocidolite asbestos fibers embedded in asphaltic bitumens or hydraulic Portland cement.
The most recognizable roofing application is corrugated transite—rigid, wavy cement sheets containing up to twenty percent asbestos fibers. Extensively utilized on agricultural barns, warehouses, and industrial sheds, transite roofs offered decades of rot-free performance. In residential housing, diamond-patterned cement shingles and asphalt mineral-surfaced shingles were standard.
| Roofing Component | Typical Material Matrix | Asbestos Content | Friability & Risk Classification |
|---|---|---|---|
| Corrugated Transite Panels | Portland cement & mineral fiber matrix | 10% to 25% Chrysotile/Crocidolite | Non-friable Category II (Friable if crushed or broken) |
| Asbestos-Cement Shingles | Pressed cement slate imitation | 15% to 30% Chrysotile | Non-friable Category II (High risk when sawed or broken) |
| Asphalt Saturated Felts | Organic felt paper infused with asphalt | 5% to 15% Chrysotile | Non-friable Category I (Flexible when intact) |
| Roof Flashing & Lap Cements | Petroleum asphalt mastic / cutback paste | 3% to 10% Chrysotile | Non-friable Category I (Tightly bound in asphalt) |
| Coal Tar Pitch Built-Up Roofs | Multiple plies of felt and tar gravel | 5% to 20% Chrysotile | Non-friable Category I (Becomes friable during mechanical tear-off) |
Weathering Degradation, Moss Growth, and Safety Dangers
While intact asbestos roofing is classified as non-friable, decades of exposure to ultraviolet radiation, acid rain, freeze-thaw cycles, and moss growth break down the surface cement binder. Over time, the outer layer erodes, exposing bare, friable mineral fibers directly to the elements.
Homeowners often create severe contamination emergencies by attempting to clean weathered asbestos roofs. Pressure washing an asbestos-cement roof blasts millions of loose microfibers into the air, contaminating downspouts, flowerbeds, and neighboring properties. Similarly, dry scraping or power grinding shingles releases dense clouds of carcinogenic dust.
| Maintenance / Removal Action | Potential Hazard Created | Regulatory Status | Recommended Safe Alternative |
|---|---|---|---|
| High-Pressure Water Washing | Aerosolizes fibers and spreads toxic slurry into soil | Prohibited by environmental regulations | Apply biocide spray at low pressure without scrubbing |
| Power Sawing / Mechanical Grinding | Generates respirable dust clouds over neighborhood | Strictly Illegal under EPA NESHAP | Unfasten panels manually using hand tools |
| Dropping Shingles from Roof Deck | Shatters brittle cement panels upon ground impact | Severe OSHA / EPA safety violation | Lower materials to ground using crane or enclosed chute |
| Encapsulation Coating | Seals weathering fibers without disturbance | Approved and recommended method | Spray elastomeric acrylic roof coating |
When an asbestos roof reaches the end of its useful lifespan, property owners must choose between encapsulation and professional abatement. If the roof deck is structurally sound, applying a thick elastomeric bridging membrane seals the weathered surface, extending roof life for fifteen to twenty years.
If full replacement is necessary, licensed abatement contractors must remove shingles intact by carefully unclipping or unscrewing fasteners, lowering panels in padded crates, and wrapping debris in 6-mil poly sheets for manifested disposal.
How to Safely Address and Manage an Asbestos Roof
Step-by-step roadmap for evaluating, maintaining, or replacing asbestos roofing assemblies.
Confirm Presence with Laboratory PLM Analysis
Collect a small broken corner fragment from a shingle while wearing a P100 respirator, misting with water, and submit to an accredited lab.
Perform Visual Structural Assessment
Examine whether panels are intact and dry or severely cracked, bowing, and shedding loose surface fibers.
Apply Low-Pressure Encapsulant Coating
If structurally sound, spray a specialized elastomeric roofing sealer at low pressure to encapsulate loose fibers and prevent weathering.
Retain Certified Abatement Roofers for Replacement
If replacement is required, hire a licensed abatement contractor who will wet-mist panels, unfasten screws manually, and lower sheets intact.
Verify Manifested Hazmat Landfill Disposal
Ensure all discarded roofing panels are double-wrapped in 6-mil plastic and transported under hazardous waste manifests to an approved disposal facility.
Frequently Asked Questions (7 Questions Answered)
Q1: Is an asbestos roof dangerous if it is not leaking?
No, if the roof is intact, undamaged, and not disturbed, it poses very little health risk because the fibers are bound in cement or asphalt.
Q2: Can I pressure wash my asbestos roof to remove moss?
Never pressure wash an asbestos roof; high-pressure water strips the cement binder and blasts toxic fibers across your yard and neighborhood.
Q3: How long does an asbestos cement roof last?
Asbestos-cement transite roofs are exceptionally durable, frequently lasting 50 to 70 years or more with proper maintenance.
Q4: Can I install a metal roof over existing asbestos shingles?
In many jurisdictions, installing furring strips and a new standing-seam metal roof over intact asbestos shingles is an approved encapsulation method.
Q5: What happens if an asbestos roof tile cracks?
A cracked tile can release fibers; apply a localized patch with outdoor silicone or elastomeric roofing mastic to seal the fracture.
Q6: How much does it cost to remove an asbestos roof?
Professional asbestos roof removal typically costs between $8 and $15 per square foot, including containment, manual unfastening, and disposal.
Q7: Can I throw old asbestos roofing shingles in a regular dumpster?
No, asbestos roofing is regulated hazardous waste and must be disposed of at licensed landfills permitted to receive toxic mineral waste.
Final Thoughts & Key Takeaways
Managing roofing asbestos requires balancing weather integrity with environmental caution. Never pressure wash, drill, or dry-saw vintage cement shingles or corrugated transite sheets. By utilizing liquid elastomeric encapsulation or retaining certified roofing abatement specialists for intact panel extraction, building owners maintain durable roof protection without endangering health.