Algae vs. Moss

One day you’ll up at your once new looking roof and notice some discoloration. If you live in the Northwest this will likely be on the North side of your home. The added sun on the South side of the roof often keeps it fairly clean. The first thing you need to do is to identify what is discoloring your roof: is it algae or is it moss? Take a look at the following photos to see how moss and algae may appear on the roof.

The large tufts of green and brown are moss. As they grow they expand and collect granules from the roof and dig their roots under your shingles. This holds water against the roof, which can cause rot, and it may allow water intrusion. The next photo is from the same roof and highlights the algae growth as well.

The dark streaks staining the roof are from algae. You can notice the algae is most prevalent in sections with lots of moss. This is because the moss holds on to water and those sections of the roof remain moist for longer and therefore grow more algae in the damp areas. By soft washing the roof we can address both the algae staining and the moss growth without causing further damage to your shingles from high pressure washing. The next photo shows the immediate effects of soft washing on roof discoloration.