Asphalt Asbestos Roof Shingles
Asphalt asbestos roof shingles were widely manufactured and installed across North America from the 1920s through the late 1970s. Formulated by blending oxidized petroleum bitumen with organic felts and ten to thirty percent chrysotile asbestos fibers, these composite shingles provided superior fire-resistance, weatherproofing, and dimensional stability before public health regulations restricted asbestos in residential building materials.
The Engineering and Manufacturing of Asbestos Asphalt Roofing
During the early twentieth century, asphalt roofing manufacturers sought additives that could improve fire resistance and prevent shingles from curling under intense solar heat. Traditional asphalt-saturated organic felt shingles were vulnerable to flying embers and degraded rapidly in harsh weather. By incorporating chrysotile asbestos fibers into the felt substrate and asphalt coating, manufacturers created composite shingles that achieved Class A fire ratings—the highest fire-safety benchmark in construction.
Asbestos fibers acted as micro-reinforcing rebar within the bitumen matrix, resisting thermal expansion, repelling moisture infiltration, and preventing cracking during freezing winter temperatures. These products were produced as multi-tab shingles, interlocking hexagonal shingles, and roll roofing felts marketed by major building suppliers including Johns-Manville, Flintkote, CertainTeed, and Philip Carey. Because the mineral fibers are embedded within dense asphalt bitumen, undamaged shingles are classified as Category I non-friable materials.
| Roofing Product Type | Manufacturing Era | Typical Asbestos Content | Friability Classification |
|---|---|---|---|
| Asphalt-Asbestos 3-Tab Shingles | 1920 to 1980 | 10% to 25% Chrysotile | Category I Non-Friable (intact bitumen) |
| Interlocking Hexagonal Shingles | 1930 to 1975 | 15% to 30% Chrysotile | Category I Non-Friable (unless brittle) |
| Asphalt-Saturated Underlayment Felt | 1925 to 1982 | 5% to 15% Chrysotile | Category I Non-Friable (flexible organic) |
| Transite Cement-Asbestos Shingles | 1910 to 1985 | 15% to 25% Chrysotile / Amosite | Category II Non-Friable (rigid Portland cement) |
Deterioration Mechanisms and Safe Teardown Protocols
While asphalt asbestos shingles are classified as non-friable when new, decades of ultraviolet solar radiation, freeze-thaw cycles, and organic degradation alter their physical integrity. Over thirty to fifty years, the volatile oils within the asphalt evaporate, leaving the bitumen dried out, brittle, and cracked. In this weathered state, walking on the roof deck or aggressively prying shingles during roof tear-offs can fracture the shingles, releasing microscopic mineral fibers into the surrounding environment.
Under federal EPA NESHAP regulations, roof demolition procedures must prevent non-friable materials from becoming friable. Roofing contractors are strictly prohibited from using high-speed rotary saws, power sanders, or dry leaf blowers on asbestos roof assemblies. Shingles must be continuously misted with surfactant-amended water to suppress dust, gently pried up using manual shingle shovels, and lowered to the ground in covered hoist containers rather than thrown into open dumpsters.
| Demolition Practice | Safety Specification | Prohibited Action | Regulatory Health Rationale |
|---|---|---|---|
| Fastener Removal | Manual shingle spade beneath nail head | Power sawing across shingle courses | Prevents mechanical fiber aerosolization |
| Dust Suppression | Continuous surfactant water misting | Dry prying or sweeping roof deck | Keeps fibers saturated and grounded |
| Waste Transport to Ground | Chute or crane hoist into lined bin | Throwing shingles off roof edge | Prevents impact breakage and neighborhood drift |
| Debris Packaging | Double 6-mil poly bags or wrapped pallets | Disposal in municipal curbside trash | Mandated by state hazardous waste laws |
Property owners considering a roof replacement can frequently choose between complete tear-off or roof encapsulation (re-roofing). If local building codes permit a second roof layer and structural rafters can support the weight, installing a layer of recovery insulation board directly over intact shingles followed by new architectural shingles is an approved, economical containment solution.
However, if multiple roof layers already exist or if roof decking is soft and rotting, complete professional abatement is required. Always engage an accredited testing laboratory to verify asbestos content before planning demolition.
How to Safely Handle Asphalt Asbestos Shingles
Step-by-step assessment and tear-off procedure for vintage asphalt roofing.
Confirm Content via Laboratory PLM Analysis
Collect a small one-square-inch core sample of shingle and underlayment felt, sending it to an NVLAP laboratory for PLM testing.
Evaluate Encapsulation vs. Complete Removal
Consult a roofing engineer to determine whether installing a second roof layer over intact shingles is structurally viable.
Implement Continuous Wet Dust Suppression
If tearing off, saturate shingle courses with amended surfactant water before and during fastener extraction to prevent dust.
Package Shingles in Certified Hazmat Bags
Carefully place intact shingles into labeled six-mil polyethylene disposal bags and manifest for transport to an authorized landfill.
Frequently Asked Questions (8 Questions Answered)
Q1: Do old asphalt roof shingles contain asbestos?
Yes, asphalt shingles manufactured between 1920 and 1980 frequently contained ten to thirty percent chrysotile asbestos for fireproofing.
Q2: Are asphalt asbestos shingles dangerous if undisturbed?
No, undisturbed shingles are non-friable and pose negligible health risks because fibers are locked within the asphalt bitumen matrix.
Q3: Can I install a new roof over asphalt asbestos shingles?
Yes, many building codes allow installing a second layer of modern shingles or metal roofing over intact existing shingles as encapsulation.
Q4: Why can't you power wash an asbestos asphalt roof?
Power washing pulverizes the weathered asphalt, atomizing millions of microscopic asbestos fibers into the surrounding neighborhood air.
Q5: How do you identify asphalt asbestos shingles?
Visual inspection cannot confirm asbestos; you must send a small sample to an accredited laboratory for Polarized Light Microscopy.
Q6: What respirator is required for asphalt shingle removal?
Workers must wear a NIOSH-approved tight-fitting elastomeric respirator equipped with P100 particulate (HEPA) filters.
Q7: How much does it cost to remove asphalt asbestos roofing?
Professional removal typically costs between $6 and $14 per square foot, depending on roof pitch, story height, and disposal fees.
Q8: Can removed asbestos shingles go into regular dumpsters?
No, asbestos roofing waste must be double-bagged in six-mil poly sheeting and transported under manifest to a permitted hazardous monofill.
Final Thoughts & Key Takeaways
Asphalt asbestos roof shingles provided outstanding durability and fire protection throughout twentieth-century construction. By understanding their material composition, avoiding abrasive power tools, and employing wet-removal or professional encapsulation methods, homeowners can safely manage aging roofing without hazardous fiber exposures.