Asphalt roofs are susceptible to stains over time. Moss, algae, and debris can accumulate on your shingles, especially if your roof is in a shaded area. In order to get the longest lifespan possible out of your roof, you'll have to clean it. Knowing how to clean your roof properly will prevent you from damaging your roof and make sure you get the most out of its lifespan.
Soap And Water
Lightly soapy water is probably the easiest and safest way to clean your roof. The soap won't harm the plants below if used in small enough quantities and it provides just enough cleaning power to remove most gunk from your roof. Just mix enough soap and water together so that it's lightly soapy. Apply it to your roof with a sprayer so there's no risk of spilling, and gently scrub your roof with a soft bristled brush. When you're finished just rinse your roof off.
While soap is powerful to remove most stains, it may not be enough to remove mildew stains. You may have to use a specialized roof cleaner or bleach solution.
If you have severe staining on your roof you can use a bleach solution. The proper ratio to use is 1 1/2 cups of bleach to two gallons of water. Use a hand sprayer to apply the solution to your roof and then scrub with a soft brush.
If using bleach makes you worry for the health of any gardens around your home, you can also use a vinegar solution. You should add vinegar to water in the same ratio as the bleach solution. Vinegar can still kill plants though in a high enough concentration. No matter what solution you choose to use, you should always rinse your roof and surrounding area with plenty of water.
What You Shouldn't Use
You should never use a pressure washer or abrasive scrubber on your roof. Pressure washers and abrasive scrubbers may damage your roof. The pressure of intense scrubbing will remove small portions of your roof and wear it down. While the damage may not be immediately visible to you, it can lead to leaks and severely shorten the lifespan of your roof.
If you don't feel comfortable climbing up on your roof and cleaning it, you can ask a local roofing contractor at companies like All Weather Exteriors to do it for you. They can send someone skilled in dealing with your roof's stains and you won't have to worry about climbing on your roof yourself. You can even schedule regular cleanings at your convenience.