What to look for from the ground
Asbestos cement roofing is cement. Almost every reliable tell follows from that one fact, and all of them are visible from a ladder at the edge, a neighbouring vantage point, or the ground with a phone camera zoomed in.
- Colour. Dull, flat, mid-grey, weathering to a chalky white-grey. Painted roofs are common in Sydney and hide this completely — check the underside in the carport or the eave instead.
- No rust, ever. Cement does not rust. An old grey roof with no rust streaks at the fixings, but with lichen, moss or dark organic growth, is a strong indicator.
- Thick, blunt edges. At the gutter line and the barge, asbestos cement is visibly thick and squared off. Metal sheeting is thin enough to see as a line.
- Fixings. Hook bolts or large-headed screws with washers through the ridge of the corrugation, often with cracks radiating from them on older sheets.
- Ridge capping in the same grey material, rather than a metal cap.
The profile: count the ridges
Corrugated asbestos cement was made in two main profiles in Australia, and the shape is the most useful single clue on the roof.
- Eleven narrow ridges with a half-lap edge — the early twentieth-century profile. Rare now, mostly on very old sheds and outbuildings.
- Seven wider, deeper ridges — the profile that dominated from the mid-1920s onward, and the reason the best-known trade name for it is Super Six.
From the ground, spacing is easier to judge than an exact count. Asbestos cement corrugations sit roughly 145 mm apart, and each one is fixed through the top of the ridge. Steel corrugated iron runs at about 76 mm — roughly twice as many ribs across the same width of roof.
Other names on the same product include Fibrolite, Durabestos, Master Seven, Standard, Tasbestos and Asbestolite. Tasbestos "Trojan Tile" was made in roughly one-metre sheets and was coloured red-brown rather than grey, which catches people out. Flat asbestos cement sheeting on a roof or eave is a different product — see fibro sheeting.
On average, corrugated asbestos cement roofing contained around 15% asbestos.
Telling it apart from metal roofing
| Asbestos cement | Galvanised iron / Colorbond | |
|---|---|---|
| Surface | Matt, chalky, holds moss and lichen | Smooth, often glossy or faded paint |
| Ageing | Flaking, surface erosion, hairline cracks | Rust, especially at laps and fixings |
| Edge | Thick and blunt, several millimetres | Thin, sheet-metal line |
| Sound | Dead thud; no drumming in rain | Rings; loud in heavy rain |
| Profile | Seven deep ridges (or eleven narrow, if very old) | Many narrow ribs, or trapezoidal ribs |
The awkward case is a roof that has been painted. Paint hides colour, texture and weathering all at once, and it is common on Sydney garages. Fall back on the edge thickness, the underside, and the age of the structure.
Weathering, gutters and tank water
An asbestos cement roof does not stay the way it was installed. The national product guide describes how daily expansion and contraction, plus decades of weather, erode the cement matrix at the surface until fibre bundles are exposed — and the resulting fine material washes into the gutters and downpipes.
Three practical consequences:
- Gutter sludge under an old asbestos roof should be treated as contaminated debris, not garden mulch, and not something to scoop out by hand on a Sunday.
- Runoff should not be used for drinking water or to fill a tank — the product guide advises against it directly.
- Heavily weathered sheeting can be assessed as friable. Material that crumbles under hand pressure is no longer the stable bonded product it was, which changes the licence class and the controls the job requires — see friable vs bonded asbestos.
This is also why "just pressure-wash it" is one of the worst things that can be done to an asbestos roof, and why repainting a badly degraded roof is often a way of postponing a job that has already become necessary.
Where it is on a Sydney property
Whole-house asbestos roofs still exist across Sydney's post-war suburbs, but the far more common survivor is the outbuilding. In order of how often we are called about them:
- Detached garages and carports, including the roof over a shared driveway.
- Back sheds and workshops, and the lean-to on the side of one.
- External laundries and old outside toilets.
- Patio, pergola and awning roofing.
- Whole roofs on fibro cottages and post-war housing that has never been re-roofed.
Commercial and industrial buildings are the other half of the picture — the product guide lists foundries, factories, warehouses, workshops and electricity substations, which is much of Sydney's older industrial stock. See commercial asbestos removal for how that work is scoped around occupied premises.
Do not walk on it
Asbestos cement roofing is fragile roofing. It is brittle when new and more brittle after forty years of Sydney sun. Falls through it are among the most serious injuries in this trade, and standing on a sheet cracks it — turning stable bonded material into broken debris and a bigger job than you started with. Identify it from the ground. If it needs to be walked, it needs a crew with fall protection.
Also, and for the same reason:
- Do not pressure-wash, water-blast or scrub the roof surface.
- Do not drill it to run a cable, mount an antenna, or fit a solar bracket.
- Do not cut a hole in it for a skylight, a vent or a flue.
- Do not break sheets down to fit them in a skip. Asbestos waste is a regulated stream in NSW and cannot go in general waste — see asbestos disposal.
Solar installation is worth calling out on its own. A pre-1990 grey roof needs to be identifiedbefore panels are quoted, because drilling mounts into asbestos cement is licensed work and most installers will not touch it.
How it gets confirmed
As with every other asbestos product, appearance is an indicator and aNATA-accredited laboratory is the answer — analysis under AS 4964-2004 on a sample taken under controls. On a roof, sampling is not a matter of snapping a corner off: the access risk is the reason it is done by someone equipped for it. See asbestos testing.
Removal, or replacement
Roofs are the one asbestos product where removal and replacement are usually the same conversation: the sheeting comes off and something has to go back on before the next storm. See asbestos roof removal and replacement for how that is sequenced, and the cost guide for the published market ranges for roof work, including why a garage roof and a house roof are priced so differently.
Where this information comes from
Profile, brand, asbestos-content and weathering details are from the national Asbestos Product Guide (opens in a new tab) published by the Asbestos and Silica Safety and Eradication Agency. General identification guidance and the pre-1990 rule of thumb are from asbestos.nsw.gov.au (opens in a new tab).