Homeowners in the bay area experience special weather conditions that they have to learn to adapt to. An area with so much moisture in the air creates an algae feeding ground, so homeowners and building owners have to watch their roofs carefully and make sure they are aware of any potentially hazardous algae growths.
Surprisingly, algae does not actually have any long term harmful effects, but it is more of an aesthetic eyesore. If it is left for too long, the stagnant moisture can begin to rot the roof membrane underneath, so it is always best to treat it sooner rather than later.
There are many different cleaning methods once the stains already appear. However, a better tactic is to try to prevent it right from the beginning. One way to do this is to install metal flashing around your chimney, or even along the top of your roof. With just these flashes of metal you can protect areas of your roof from algae. Metal is toxic for algae, so when it rains it carries trace amounts of zinc and copper over top of the shingles. The rain only run directly down from any areas with metal flashing, so any section of your roof that is without metal will show a stark difference in its resistance to stains.
Algae proof shingles are actually becoming a really popular option for contractors to use. By mixing copper elements directly into the roofing shingles, it creates an algae resistant formula.
However, if it is past the time for algae prevention and you need to clean off some already existent stains, do not worry. It can be done in only a few steps.
1) Make sure you have the right chemicals
Many people make the mistake of going straight to a chlorine bleach cleaning agent. This method is not recommended because the chlorine bleach is corrosive and will leave your shingles looking significantly discolored. Not to mention the fact that while bleach will kill the surface algae, it does not sink deep enough to eliminate the algae colonies altogether, so you will see the stains return fairly quickly.
2) Prepare the area
Preferably, you should choose a somewhat overcast, but not windy day to clean your roof. Prepare your roof by removing any stray leaves, sticks, or dirt. Then, you will want to repair any damaged or loose shingles and clean out your gutters so that the spray can drain freely.
3) Spraying the shingles
First, you will want to spray down your shingles with just water to cool down your roof and prepare them for the cleaning spray. Once they are fresh and ready you will want to mix your cleaning solution and water at a 1:7 ratio. Using a pump sprayer you are then ready to spray down all of your shingles. You will want to apply your cleaning solution evenly across the stains and other shingles and enjoy your new clean roof.