Shingle roof cleaning is usually done because mold, mildew, algae or fungi have started growing. This is not only unsightly, it poses a risk to the waterproofing of your roof. Check with your manufacturer before cleaning to see if there are any products which will void your warranty.
Spray Down With Hose/Pressure Washer
While you should never use a high-powered pressure washer, the average garden hose or low-pressure washer easily removes fungi. To avoid granule removal and water damage, keep the spray a few feet from the shingles and spray downwards.
Gently Scrub With Brush
Using a scrub brush with soft bristles will remove dirt and most fungi, but you must do it very delicately. Applying too much pressure will scrape off the granules and damage the shingle.
Mix a Bleach Solution
There are chlorine bleach and oxygen bleach solutions on the market. Chlorine bleach can harm shingles if not applied properly. Oxygen bleach is safer and less toxic.
Apply Copper Sulfate
Copper sulfate can be sprayed onto roof mildew, allowed to sit until the mildew becomes a brownish color, and then swept off with a broom. After removing the mildew, spray the roof down with water and make sure to rinse out metal gutters.
However you clean your roof, make sure to take safety precautions, as moisture and whatever is growing there makes for a slick surface.