Covering Asbestos Siding
Exterior building envelopes built throughout the twentieth century relied heavily on asbestos-cement products, commonly commercialized under trade names such as Transite, Eternit, and Careystone. Manufactured by blending portland cement with ten to thirty percent chrysotile or amphibole asbestos fibers, asbestos-cement roofing shingles, corrugated sheets, and siding panels provided unprecedented weatherproofing, rot resistance, and fire immunity. While intact exterior panels remain non-friable, aging, weathering, power washing, and breakage during siding replacement require specialized handling to prevent environmental contamination.
Characteristics and Composition of Transite Asbestos Siding and Roofing
Transite shingles and siding panels represent dense, rigid composite products engineered for extreme environmental durability. Unlike organic asphalt shingles or wooden clapboards, asbestos-cement siding will not rot, warp, burn, or succumb to insect infestation. Shingles typically feature distinctive wavy bottom edges, embossed faux-wood grain striations, and uniform twelve-inch by twenty-four-inch rectangular dimensions fastened directly to wall sheathing with galvanized ring-shank nails.
Under undisturbed conditions, the portland cement matrix securely encapsulates asbestos fibers. However, decades of atmospheric weathering, acid rain, and solar ultraviolet degradation slowly erode the outer cement paste, exposing bare asbestos fibers on older exterior walls and roofs. The primary hazard occurs when contractors or homeowners attempt to cut shingles with circular saws, blast surfaces with high-pressure power washers, or shatter siding during demolition.
Examine the technical specifications, asbestos content, and performance characteristics of exterior asbestos-cement products:
| Exterior Product Type | Common Trade Name | Asbestos Content | Physical Composition | Expected Service Lifespan |
|---|---|---|---|---|
| Asbestos Cement Siding Shingles | Transite, Careystone | 15% to 30% Chrysotile / Amosite | Hydraulic cement, mineral pigments, silicate fibers | 60 to 100+ years |
| Corrugated Roofing Panels | Transite Industrial Roofing | 20% to 35% Chrysotile | Heavy-gauge corrugated cementitious sheets | 75+ years |
| Roofing Underlayment & Felts | Johns-Manville Asbestos Felt | 10% to 20% Chrysotile | Asphalt-saturated organic asbestos paper | 30 to 50 years |
| Roof Flashing & Ridge Mastic | Black Asbestos Plastic Cement | 5% to 15% Chrysotile | Petroleum asphalt mastic with mineral fibers | 25 to 40 years |
Remediation Options: Siding Over vs. Complete Exterior Removal
When renovating a home with existing Transite siding, property owners generally evaluate two primary strategies: siding over (encapsulation) or complete removal. Siding over existing asbestos panels is fully recognized by municipal building departments and environmental protection agencies. Contractors install a 3/8-inch foam backer board or fanfold insulation directly over the flat Transite shingles, subsequently nailing modern vinyl, composite, or fiber-cement siding into underlying wall studs.
Siding over saves thousands of dollars in hazardous removal fees, avoids the risk of wall sheathing damage, and adds significant exterior R-value thermal insulation. However, if shingles are severely shattered, crumbling, or if the homeowner plans structural additions or window replacements, full professional removal is necessary. Removal involves manually pulling individual fastener nails using specialized shingle-ripper tools, carefully lifting intact shingles without snapping, and wrapping them in 6-mil poly bundles for hazardous disposal.
Compare costs, safety, and operational considerations between siding over and full siding removal:
| Project Consideration | Siding Over (Vinyl Overlay) | Complete Professional Removal | DIY Unpermitted Removal (Dangerous) |
|---|---|---|---|
| Average Cost Range | $4 to $8 per sq ft (New siding cost) | $7 to $15 per sq ft (Removal only) | Low upfront; high legal liability |
| Hazardous Waste Disposal | None; materials stay on wall | Mandatory certified asbestos landfill | Illegal dumping fines up to $25,000 |
| Air Quality Safety | High; zero shingle breakage | High when wet manual removal is used | Extremely poor; soil & yard contamination |
| Exterior Thermal Insulation | Adds R-2 to R-4 foam backer value | No insulation added by removal alone | Exposes bare historic wall sheathing |
Safe Replacement Shingles and Minor Siding Repairs
When single Transite shingles are cracked or chipped by lawnmower pebbles or fallen branches, homeowners do not need to replace their entire exterior wall. Several architectural specialty manufacturers produce non-asbestos fiber-cement replacement shingles—such as GAF WeatherSide—that match the exact dimensions, wavy edge contours, and textured surfaces of historic 12x24-inch asbestos shingles.
To repair an isolated damaged shingle, carefully slide a shingle ripper tool beneath the cracked unit to slice the holding nails, mist the area with soapy water, gently extract the broken pieces, and slide the new non-asbestos replacement shingle into place, securing it with hot-dipped galvanized siding nails.
How to Safely Manage and Repair Asbestos Siding in 5 Steps
Follow these step-by-step procedures to repair isolated cracked shingles or prepare exterior walls for safe siding overlay.
Perform a Thorough Exterior Visual Inspection
Walk your home perimeter to identify cracked, loose, or weathered shingles, checking for fiber erosion or missing fastener nails.
Never Power Wash or Mechanically Grind Shingles
Strictly avoid high-pressure washing or wire brushing, which strips cement binders and releases millions of fibers into the surrounding yard.
Stabilize Minor Cracks with Exterior Elastomeric Sealant
Seal small hairline fractures using high-grade exterior acrylic or polyurethane caulk, smoothing with a damp cloth to prevent water penetration.
Replace Broken Units with Non-Asbestos Fiber-Cement Shingles
Slide a shingle ripper under damaged tiles to sever nails, remove broken shards while damp, and install modern fiber-cement replica shingles.
Install Rigid Fanfold Foam and Siding Overlay
If re-siding, fasten rigid fanfold insulation directly over the existing Transite siding and nail modern vinyl or composite siding into wall studs.
Frequently Asked Questions (9 Questions Answered)
Q1: Is asbestos siding dangerous on a house?
Intact asbestos siding is generally not dangerous because the fibers are bound tightly in cement. It only poses a health hazard if cut, broken, sanded, or power washed.
Q2: Can you put new siding over asbestos siding?
Yes. Siding over existing Transite shingles with fanfold foam insulation and new vinyl or composite siding is an approved and cost-effective encapsulation method.
Q3: Can you paint asbestos siding?
Yes. Painting asbestos siding with high-quality 100 percent acrylic latex paint encapsulates the surface, binds loose fibers, and extends the siding's lifespan.
Q4: How do you tell if siding is asbestos?
Asbestos siding is typically hard, brittle, fireproof, 12x24 inches in size, features wavy edges or faux-wood grain, and was installed between 1920 and the 1970s.
Q5: How much does it cost to remove asbestos siding?
Professional removal typically costs between $7 and $15 per square foot, including certified containment, manual nail pulling, and hazardous waste disposal.
Q6: Where can I find replacement shingles for broken asbestos siding?
Modern non-asbestos fiber-cement replica shingles, such as GAF WeatherSide, are manufactured in matching dimensions and textures for spot repairs.
Q7: Can I power wash my asbestos siding?
Never power wash asbestos siding. High-pressure water strips away the cement binder, pulverizing fibers and contaminating your soil, yard, and neighbors' property.
Q8: How do you dispose of asbestos siding legally?
Asbestos siding must be kept wet, double-bagged in 6-mil poly bags with OSHA warning labels, and transported to a landfill permitted for asbestos waste.
Q9: Does carpet padding trap asbestos dust from underlying tiles?
While carpet padding may physically cover old tiles, standard carpet tack-strip nailing frequently shatters brittle tiles, leaving pulverized fibers trapped underneath that get aerosolized during future carpet removal.
Final Thoughts & Key Takeaways
In conclusion, understanding covering asbestos siding provides essential clarity, practical strategies, and actionable advice. By incorporating these foundational insights, adhering to verified safety guidelines, and following structured best practices, you ensure reliable, long-term outcomes while preventing common mistakes. Stay informed, consult certified professionals when needed, and maintain consistent quality care.