Your roof is exposed to an entire wealth of good and bad natural elements.
In Brisbane, it can be hit by hours of intense sunlight, smashed by hail and other debris, and soaked by heavy rainfall. If you live in an area where it snows, it can be covered in ice and water for hours at a time. As time progresses, these conditions can cause grime and algae to form, no matter how impervious your roof is. Because of these superficial and more malignant forms of damage, occasionally cleaning your roof can be a good idea. The best way of doing this? With a pressure washer.