Asbestos on Roof
Asbestos on roof structures is frequently encountered on vintage residential houses, commercial warehouses, and agricultural barns built between 1900 and the mid-1980s. Incorporated into corrugated transite cement panels, imitation slate shingles, and bituminous roofing felts for non-combustible durability, asbestos roofs offer decades of weather resistance but present significant environmental and health risks when weathered, moss-covered, or improperly cleaned.
Common Types of Exterior Asbestos Roof Systems
During the twentieth century, building codes demanded rigorous fire ratings for commercial and domestic roof envelopes to prevent flying embers from igniting structural roof timber. Manufacturers met this demand by combining chrysotile or crocidolite asbestos fibers with Portland cement or petroleum asphalts.
The most widely installed residential application was asbestos-cement roofing shingles, manufactured to mimic natural quarried slate. On industrial and agricultural buildings, large corrugated transite sheets measuring eight to twelve feet in length became standard, offering completely rot-proof, termite-proof, and fire-resistant roofing at low initial cost.
| Roof System Type | Material Composition | Expected Service Lifespan | Friability & Risk Dynamics |
|---|---|---|---|
| Corrugated Transite Panels | Portland cement & 15% to 25% chrysotile/crocidolite | 50 to 80+ Years | Non-friable Category II (Friable if cut, cracked, or crushed) |
| Asbestos-Cement Shingles | Pressed cement slate substitute (15% to 30% asbestos) | 40 to 60 Years | Non-friable Category II (High risk during power saw cutting) |
| Built-Up Coal Tar & Felt | Multiple plies of asphalt-saturated asbestos felt | 20 to 30 Years | Non-friable Category I (Pulverized during mechanical tear-off) |
| Roof Flashing & Lap Mastic | Asphaltic bitumen paste blended with asbestos fibers | 15 to 25 Years | Non-friable Category I (Tightly bound in bitumen) |
Weathering, Lichen Growth, and Prohibited Maintenance Practices
While intact asbestos roofing is legally classified as non-friable, decades of exposure to ultraviolet solar radiation, acid rain, freeze-thaw cycles, and organic moss growth inevitably break down the surface cement binder. Over time, the outer cement matrix erodes, exposing loose mineral fibers directly to rain and wind.
Homeowners often cause severe environmental contamination by attempting DIY roof maintenance. Using a high-pressure power washer on an asbestos roof is illegal in many jurisdictions because the high-pressure water stream pulverizes the weathered cement, blasting millions of toxic fibers into the air and contaminating downspouts, gardens, and neighboring properties.
| Roof Maintenance Action | Operational Hazard Generated | Regulatory Legality | Approved Alternative Method |
|---|---|---|---|
| High-Pressure Power Washing | Aerosolizes fibers and spreads toxic slurry into soil | Strictly Prohibited by environmental laws | Apply biocide spray at low pressure (< 50 psi) |
| Mechanical Wire Brushing | Scrapes cement binder into dry airborne dust clouds | Prohibited under OSHA / EPA NESHAP | Low-pressure chemical moss killer with soft rinse |
| Walking Directly on Transite | Brittle panels can crack and collapse underfoot | Severe safety and fall hazard | Use crawling boards or roof ladders spanning purlins |
| Elastomeric Encapsulation | Seals weathered surface without disturbing fibers | Fully Approved and recommended | Spray high-build elastomeric acrylic roof membrane |
When an asbestos roof reaches the end of its useful lifespan, property owners must choose between encapsulation and complete replacement. If the roof deck is structurally sound, applying a heavy-duty elastomeric acrylic coating encapsulates weathered fibers, stops leaks, and extends roof life for another ten to twenty years.
If full replacement is necessary, licensed asbestos abatement contractors must remove panels intact. Technicians wet the shingles with surfactant, unfasten screws or nails manually with hand tools, lower panels in padded slings, and double-wrap debris in 6-mil plastic for transport to a licensed landfill.
How to Safely Manage and Maintain an Asbestos Roof
Step-by-step roadmap for inspecting, cleaning, and replacing an asbestos roof.
Confirm Asbestos Content with Lab Testing
Collect a small broken corner fragment from a shingle while wearing a P100 respirator, misting with water, and submit it to an NVLAP laboratory.
Inspect Roof Structural Condition from Ground
Use binoculars from ground level to inspect shingles for cracking, missing panels, or heavy moss without walking on brittle panels.
Apply Low-Pressure Chemical Biocide for Moss
Treat moss and lichen with a garden sprayer applying approved moss-killing biocide at low pressure without wire brushing or power washing.
Apply High-Build Elastomeric Coating
Seal sound weathered shingles with an airless spray application of thick elastomeric acrylic coating to encapsulate fibers permanently.
Hire Certified Abatement Roofers for Removal
When replacing, retain a licensed abatement company to unfasten fasteners manually, lower panels intact, and manifest waste at a certified landfill.
Frequently Asked Questions (7 Questions Answered)
Q1: Is an asbestos roof dangerous to live under?
No, if the roof is intact, in good condition, and not disturbed, it poses very little health risk because the fibers are bound in cement.
Q2: Can I power wash moss off my asbestos roof?
Never power 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 you put a new roof over an existing asbestos roof?
Yes, installing furring strips and an over-roof metal sheet system over intact asbestos shingles is an approved encapsulation method.
Q5: How much does it cost to remove an asbestos roof?
Professional asbestos roof removal typically costs between $8 and $16 per square foot, including containment, labor, and hazardous disposal.
Q6: Can I walk on an asbestos roof?
Avoid walking on asbestos roofs; aged panels are brittle and can shatter under human weight, presenting severe fall and contamination risks.
Q7: Where does discarded asbestos roofing go?
It must be wrapped in 6-mil plastic and transported under hazardous waste manifests to landfills licensed to receive asbestos waste.
Final Thoughts & Key Takeaways
Having asbestos on roof assemblies does not require immediate panic, as intact cement panels present minimal risk while left undisturbed. Never pressure wash, scrape, or power-saw older cement shingles. By utilizing low-pressure elastomeric encapsulation or hiring licensed abatement contractors for intact removal, property owners ensure durable weather protection while protecting household health.