Asbestos roofing was the dominant choice for New Zealand residential and commercial buildings from the late 1940s through the 1980s. Millions of square metres of asbestos-cement (AC) roofing were installed across the country during this period and a significant proportion of it remains in place today. Knowing how to identify an asbestos roof, and what to do if you suspect one, is essential knowledge for any NZ homeowner, landlord, or building professional.
Important Warning
Never touch, disturb, or attempt to sample suspected asbestos roofing yourself. Even walking on an asbestos-cement roof can crack the material and release fibres. Always call a licensed asbestos professional to inspect and test your roof.
The Age Rule Start Here
The single most reliable indicator of asbestos roofing is age. In New Zealand:
- Homes built before 1940: Low asbestos risk in roofing (AC products not yet widely available)
- Homes built 1940 1990: High asbestos risk this is the peak asbestos-cement era
- Homes built after 1990: Very low risk (phase-out was well advanced)
- Homes built after 2000: Negligible risk from original materials (comprehensive import ban in effect)
If your property was built or significantly reroofed during the 1940 1990 window, asbestos-cement roofing should be assumed present until proven otherwise by laboratory testing.
Visual Signs of an Asbestos Cement Roof
While you should never touch or disturb suspected asbestos, there are visual signs you can observe safely from the ground or a safe distance:
1. Corrugated Profile with Flat-Looking Texture
Traditional asbestos-cement corrugated roofing sheets have a distinctive appearance: a corrugated profile (similar to corrugated iron) but with a flat, grey, slightly rough cement texture rather than the shiny metallic finish of steel corrugated iron. The sheets are typically 1.8 2.4 metres long and the corrugation profile is consistent across the entire sheet.
2. Grey-Green Colouring with Algae Growth
Older asbestos-cement roofing is typically a weathered grey or grey-green colour, often with significant lichen or algae growth. Unlike metal roofing, asbestos-cement is porous and absorbs moisture, which encourages biological growth. Heavily algae-covered roofing that has a rough, textured appearance (not smooth and metallic) is a strong indicator of AC roofing.
3. Crumbling, Flaking, or Pitting Surface
Weathered asbestos-cement roofing often shows surface deterioration: pitting, surface erosion, crumbling edges, or flaking corners. This surface breakdown is known as "friability" and is a key indicator of asbestos-cement aging. Importantly, surface breakdown also indicates that fibres may be releasing making urgent professional assessment essential.
4. Heavy Overlapping Sheet Pattern
Asbestos-cement roofing was typically installed in overlapping sheets with a regular pattern of fixing holes and a pronounced overlap at ridges, hips, and valleys. The sheet-to-sheet overlap is typically more pronounced than in modern metal roofing systems.
5. Cracked or Missing Sheets
Asbestos-cement becomes increasingly brittle with age. Cracked, broken, or missing roof sheets in an older property are a significant warning sign both of possible asbestos content and of immediate fibre release risk.
Did You Know?
Asbestos-cement roofing sheets are heavier than steel corrugated iron typically 15 20 kg per square metre versus 4 6 kg for steel. If you've ever noticed that your old roof seems unusually heavy, that's consistent with asbestos-cement content.
Types of Asbestos Roofing Materials in NZ
Several distinct asbestos-containing roofing products were used in New Zealand:
- Corrugate AC sheeting: The most common corrugated sheets used as the primary roof cladding
- Flat AC sheeting: Used for fascias, bargeboards, soffits, and some flat roof sections
- AC roof tiles: Less common but used in some areas look like a pressed cement tile
- Bituminous roofing felt: Some older felt products contained asbestos fibres
- Roofing underlay: Some older paper-based underlays contained asbestos fibres
What You Cannot Tell Visually
It is critically important to understand that you cannot confirm or deny the presence of asbestos through visual inspection alone. Many materials that look like they could contain asbestos grey corrugated sheets, fibrous-looking boards may not, and vice versa. Some asbestos-containing materials look perfectly normal and modern.
The only way to confirm asbestos is through laboratory testing of a sample collected by a trained professional. IANZ-accredited laboratories use polarised light microscopy or transmission electron microscopy to identify asbestos fibres in building materials. JP Asbestos can arrange sampling and analysis with results typically available within 2 5 working days.
What to Do If You Suspect Asbestos Roofing
- Don't touch it or walk on it. Even stepping on an asbestos-cement roof can crack it and release fibres.
- Don't wash it. High-pressure cleaning of asbestos roofing releases large quantities of fibres and is illegal in NZ.
- Call a licensed professional. Contact JP Asbestos for an inspection and sampling service.
- Get it tested. Arrange IANZ-accredited laboratory analysis to confirm or rule out asbestos.
- Decide on management or removal. Based on the condition and test results, determine whether the material should be managed in place, encapsulated, or removed.
Summary
If your property was built between 1940 and 1990, you should treat any grey corrugated cement-style roofing as potentially containing asbestos until proven otherwise by laboratory testing. Visual identification can suggest asbestos but cannot confirm it. Never disturb suspected asbestos roofing call a licensed professional like JP Asbestos for inspection, testing, and safe removal.
Not Sure About Your Roof?
JP Asbestos provides professional roof inspections, bulk sampling, and IANZ-accredited testing across Auckland and NZ-wide.
