It is possible that over time, unsightly stains may appear on your roof. These are caused by moisture, which may alter the color of some roofing materials or favor the appearance of mold and mildew that also stain the roof.
Mold and mildew are often found on the northern part of the roof which is not so exposed to the sun; if leaves and other debris remain on the roof for a longer period, they retain moisture and allow mold and mildew formation. These stains can be cleaned easily with special solutions, often including chemicals, to destroy potential bacteria and microbes that can spread from the roof to the walls inside the house, if they are not removed promptly. Before using chemical cleaning solutions, an informed Denver roofer recommends testing them on a small area, to see how the material reacts under the action of chemical ingredients.
Sometimes simply washing the roof can be enough to remove the stains. However, it is also possible that the stains indicate a worn out and degraded roof profile; in this case, repairs or even a roof replacement might be in order.
If you find that your roof has what appear to be water stains, contact a specialist to determine what is to be done about them.