Concrete or clay tiles – blocked drainage

Drainage channels under the side laps of tiles have become blocked


Moss growth under side laps


Moss growth under side laps


  • clean roof regularly with a solution of 1 part household bleach to 4 parts water to restrict moss growth; brush on with a stiff broom or wire brush. Do not use where the water is collected for drinking.
  • nail a 150 mm wide copper strip along the roof ridge; alternatively install copper ridge flashing – the copper oxide solution produced by the rain is toxic and will restrict moss growth. Check that copper is compatible with adjacent building materials such as guttering and downpipes.
  • Do not waterblast as this can force water up between the tiles.