Bitumen-impregnated sheets – deterioration of roofing

With one particular product imported from the 1990s to the mid 2000s, there have been cases where the bitumen coating has been found to break down, leading to water reaching the cellulose fibres inside the material and subsequent product failure. If you have bitumen-impregnated roof or wall cladding that was installed in this period, we recommend you inspect it closely at least once a year.

 

Causes

The roof remains continuously damp due to insufficient cleaning or overhanging branches resulting in the accumulation of leaf debris 

The roofing is at the end of its serviceable life

Listed under: Roof, cladding, moisture, roof cladding, bitumen-impregnated sheets

Cause

The roof remains continuously damp due to insufficient cleaning or overhanging branches resulting in the accumulation of leaf debris 

Repair

  • cut back overhanging branches that may be keeping the roof wet or dropping leaves onto it
  • remove debris and moss regularly but avoid walking on brittle roofing such as this. You can find more details in the WorkSafe publication Working on roofs
  • where degredation is minor and limited to the surface of the cladding, coating with 2 coats of good quality acrylic paint may be at least a temporary solution, but ask the cladding supplier for their advice first. Solvent-based paints should not be used
  • if the damage is serious and/or the roof is leaking, replace the roofing without delay. If the roofing has performed satisfactorily for over 15 years, it can be replaced with comparable lightweight roofing material without a building consent
  • if the roof was installed less than 15 years ago, or it will be replaced with a very different type of roofing (such as clay tiles, which are much heavier), replacing it will require a building consent
  • if there is a possibility that the roof has been leaking for some time, engage a building surveyor to check the roof space for potential damage

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Cause

The roofing is at the end of its serviceable life

Repair

  • replace the roofing. If the roofing has performed satisfactorily for over 15 years, it can be replaced with a comparable lightweight roofing material without a building consent
  • if the roof was installed less than 15 years ago, or it will be replaced with a very different type of roofing (such as clay tiles, which are much heavier), replacing it will require a building consent

 

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