Homeowners could spend days reading everything there is to know about roof stains and what to do about them. We've been removing those stains for 10 years now, day in and day out, so we have the necessary expertise. Here's what is going on up there:
Algae spores present in the atmosphere land on your roof all the time. If an area happens to be damp and shaded from the sun, algae and possibly moss, lichen, etc. start to flourish. You may notice your roof stains are worse on the shady side of your roof. In order to grow, algae needs nourishment, which it finds inside your shingles in the form of a limestone filler. In other words, algae is eating your shingles, which, as we all know, are pretty important in protecting your home. If allowed to grow long enough, you most likely will be looking at a premature and costly roof replacement.