Asbestos cement siding and roofing: keep or remove?

What it is

From the 1920s into the 1980s, cement was reinforced with asbestos fibre to make thin, strong, fireproof and rot-proof building products. They were widely used on Canadian houses, garages, cottages and farm buildings:

• Siding shingles, usually about 30 by 60 centimetres, often with a wavy or straight bottom edge and a pressed wood-grain or stippled texture
• Roofing shingles and slates, sometimes in a diamond or hexagonal pattern
• Flat sheets used for soffits, porch ceilings, skirting and wall panels
• Corrugated sheets on garages, sheds and barns
• Pipes and flues

The trade names included Transite and Johns-Manville, and the material is often simply called transite.

Recognising it

• Hard, dense and brittle, like thin slate or unglazed tile
• A sharp, ringing sound when tapped, not the dull sound of wood or vinyl
• Grey right through where chipped or broken, even if painted
• Fixed with exposed nails, usually two or three near the bottom edge of each shingle
• Sometimes a dimpled pattern on the back
• Does not rot, burn or dent, but cracks and snaps

Modern fibre cement siding looks similar and contains no asbestos. It has been made without it since the 1980s, generally comes in long planks, and is on newer houses. Age is the best guide, and a laboratory test of a small piece settles it.

Older siding is often hidden. Vinyl or aluminium was frequently installed straight over asbestos cement shingles, and they come to light during renovations.

Is it dangerous?

The fibres are locked into the cement. This is a non-friable material: it cannot be crumbled by hand. While it is intact and undisturbed, it releases very little, and Health Canada’s general advice is that asbestos-containing materials in good condition and left alone pose little risk.

The risk comes from making dust:

• Cutting or sawing
• Drilling
• Sanding or grinding
• Breaking it up
• Pressure washing, which erodes the cement surface and releases fibres
• Scraping or wire brushing

Very weathered material can become soft and crumbly at the surface, especially old roofing. That deserves more caution.

Living with it

Asbestos cement siding in good condition can stay for decades. Sensible care:

• Leave it alone as far as possible
• Do not pressure wash. Clean gently with a soft brush, a garden hose and mild detergent if you must.
• Paint it. It takes paint well. Prepare the surface by washing only. No sanding or scraping.
• Repair small damage by sealing cracks with exterior caulk
• Replace a broken shingle with a non-asbestos fibre cement shingle made to match the old profiles
• Tell tradespeople before they drill for a vent, cable or light fitting

Covering it

New siding is sometimes installed over the old. This avoids removal, but:

• Nailing through the old shingles cracks them, so furring strips fixed at the framing are the usual method, and it is still work on asbestos material
• The asbestos remains and should be disclosed to future contractors and buyers
• It adds thickness at windows and doors

Removal

Removal is usual before an addition, new windows that change openings, new siding installed properly, or demolition. Roofing is removed when it is leaking or at the end of its life.

Ontario Regulation 278/05 governs the work when done by a contractor or employer. It classifies jobs as Type 1, 2 or 3:

• Removing non-friable asbestos material without breaking, cutting, drilling, abrading, grinding, sanding or vibrating it is generally a Type 1 operation, the lowest level. Careful removal of whole shingles by taking out the nails fits here.
• Where the material has to be broken, cut or drilled, it generally remains Type 1 only if it is wetted and worked with non-powered hand tools. Done dry with hand tools, or with power tools fitted with HEPA dust collection, it is generally Type 2, with greater precautions.
• Power tools without HEPA dust collection move the job to Type 3.

In practice a careful removal means:

• Keeping the material wet
• Removing nails and lifting shingles off whole, not prying and snapping
• Lowering pieces to the ground, not dropping them
• Plastic sheeting on the ground to catch fragments
• Windows and doors closed, and neighbours informed
• Workers in respirators and disposable coveralls, as the type of operation requires
• Double bagging or wrapping in heavy plastic, sealed and labelled
• Cleaning up fragments by hand and with HEPA vacuums, not by sweeping

Disposal

Asbestos waste in Ontario is handled under the province’s waste regulation. It must be sealed in rigid containers or double bags, labelled, and taken to a landfill that accepts asbestos, usually by appointment. It cannot go in household rubbish or a mixed renovation bin. Ask the contractor for the disposal record.

Can a homeowner do it?

The regulation’s duties fall on employers and contractors, and it does not apply to an owner working on their own occupied house. The disposal rules still apply, and so does the risk. Health authorities recommend hiring trained people, especially for roofing, which adds working at height on a brittle surface. Asbestos cement roofs will not bear a person’s weight reliably and people have fallen through them.

After a storm, fire or impact

Broken asbestos cement from hail, wind, a fallen tree or a fire should be treated as asbestos waste.

• Keep people and pets away from the debris
• Do not sweep, rake or mow over it
• Dampen fragments gently and cover them with plastic
• Have it collected and the area cleaned by a contractor equipped for it
• Tell your insurer. Where the damage is from an insured cause, handling the asbestos safely is normally part of the repair claim.

Buying or selling

Asbestos cement siding is common on older houses and is not usually a reason to walk away. Inspectors typically report it as present and note its condition. Buyers should budget for careful handling if they plan to re-clad or extend. Some insurers ask about it, so check with your broker.

More: asbestos removal and abatement.