How Moss Damages Asbestos Cement Roof Sheets | Long-Term Effects & Prevention

Asbestos cement roof sheets were once widely used in industrial, commercial, agricultural & domestic buildings. However, over time, these roofs face a silent but serious threat—moss growth. Moss doesn't just affect the appearance of the roof; it actively contributes to the deterioration of asbestos cement roofing materials.

In this article, we explore why moss grows on asbestos sheets, how it damages them, and what property owners can do to prevent long-term structural issues.

Why Does Moss Grow on Asbestos Cement Roofs?

Moss is a non-vascular plant that doesn't require soil to thrive. Instead, it uses moisture and a stable surface to establish itself—making asbestos cement roofs the perfect host.

Key reasons moss thrives on asbestos roofing:

• Porous Surface: The rough, fibrous texture of asbestos cement allows moss to anchor easily.

• Moisture Retention: Roofs exposed to frequent rain or humidity create an ideal environment.

• Shaded Areas: Buildings surrounded by trees or in low-sunlight regions are especially prone.

  
  

How Moss Damages Asbestos Cement Roof Sheets:

While moss may appear harmless, its presence can have serious consequences for the integrity of asbestos cement sheets.

1. Moisture Retention & Added Weight

Moss acts like a sponge. It absorbs and retains large amounts of water, making your roof heavier. This persistent dampness promotes wear and adds stress to roofing materials, especially around joints and fastenings.

2. Structural Penetration

Moss uses tiny structures called rhizoids to grip and penetrate the cement matrix. Over time, these structures disturb the binder holding the asbestos and cement together. This weakens the sheet, exposing more asbestos fibres and accelerating material decay.

3. Freeze-Thaw Damage

During cold months, trapped moisture within the moss can freeze and expand. This causes small cracks in the roofing sheets to widen, accelerating deterioration—especially in temperate climates.

Long-Term Risks of Moss on Asbestos Roofs:

Ignoring moss on your asbestos cement roofing can lead to:

• Material Breakdown: Gradual erosion of the cement binder.

• Asbestos Fibre Exposure: Damaged sheets may release hazardous fibres.

• Costly Repairs or Replacement: The longer you wait, the more expensive the fix.

• Structural Hazards: In extreme cases, moss damage can compromise roof stability.

How to Prevent Moss Damage on Asbestos Roof Sheets:

✅ 1. Regular Roof Inspections

Check your asbestos roof at least once a year—especially after rainy seasons or heavy storms. Look for dark green patches, pooling water, and debris buildup.

✅ 2. Safe Moss Removal

Avoid pressure washing, which can disturb asbestos fibres. Instead, use an asbestos professional with specialised equipment & approved methods to remove moss safely and in compliance with guidance & regulations.

✅ 3. Moss Prevention Treatments

Fungicidal washes and moss inhibitors can be applied to discourage future growth. Be sure to use products approved for asbestos-containing materials & seek guidance.

✅ 4. Consider Roof Replacement

If the roof is severely compromised, a full asbestos roof replacement might be the safest long-term solution. Always use trusted asbestos contractors with the appropriate training, experience & insurances in place.

Conclusion: Moss and Asbestos Don’t Mix:

Moss may seem harmless, but when it comes to asbestos cement roofing, it poses a serious threat. Its ability to trap moisture, disturb the structural matrix, and accelerate wear makes it a silent destroyer of these once-durable roofing materials.

Whether you're managing an industrial building, farm structure, or an older property, routine maintenance and early moss removal can prolong the life of your asbestos roof and reduce health and safety risks.