Why do colorbond roofs get so dirty? It’s a combination of dust, pollution, mould, lichen, algae, bird and animal droppings over time. Colorbond roofs will get dirty quicker if they are surrounded by trees which shade the roof and drop leaves and debris. Your roof will probably need cleaning every 2-3 years. This house at Peregian Springs needed a clean, so we worked our magic and got rid of all the grime, and cleaned the gutters and solar panels too. Looks so much better, and should last for years.