Cleaning your roof—and particularly your drainage system—is an important part of fall and winter home maintenance. Rainy, wet winter weather offers the perfect opportunity for algae and moss to reproduce—not exactly the best look! But regular roof cleanings reduce the chances of algae, moss, and lichen growth. And that’s important, since overactive fungi can eventually eat through your shingles and decking, which causes rot, leaks, and all kinds of problems.

However, if you’re headed for a hard freeze, you obviously don’t want to start cleaning your roof. First of all, that can create hazardous conditions for your roof cleaner. And just like you wouldn’t want to wash your walkways in subzero temperatures, a frigid roof wash could create ice dams—slabs of ice on your roof that can lead to water infiltration. To avoid a problem like that, wait until the weather is amenable (ideally at least 50 degrees Fahrenheit), and follow the tips below to get a clean slate without any roofing hazards!


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Always Hire a Professional

It’s really not advisable to climb up on your roof and do a roof cleaning yourself. The roof cleaning kits for sale at hardware stores often contain petroleum-based cleaners that can damage delicate asphalt shingles. And while you may be able to reach your roof from the ground with a hose, pure water isn’t really going to get to the root reason for your roof cleaning—that is, algae and moss.

Instead, hire a professional roof cleaning service to wash away algae, moss, and dark streaks. Look for a pro that’s certified by the RCIA, a.k.a the Roof Cleaning Institute of America. Also, ask your contractor what kind of cleaning solutions they use and whether or not they use pressure washers. Anything over about 30 PSI (about the strength of a garden hose) is too rough for asphalt shingles, so if your cleaner uses one, go with another company!

Ice dams and snow on roof and gutters

Other Ways to Prevent Algae

Once you have your roof cleaned, there are ways to reduce the likelihood of algae and moss from returning. The methods described below will help you avoid another fungi outbreak and keep your roof living its best life.

  • Install Zinc or Copper Sheets Along the Ridge of the Roof. High levels of copper are poisonous to most living things, algae and moss included. Zinc or copper strips installed as flashing or beneath courses of new shingles can deter new growth as rain washes down the roof, carrying a mixture of copper wash along with it. However, these products come with risks too—they may be harmful to nearby plant life or aquatic habitats as well.
  • Use a Moss or Algae Killer. Similarly, copper mixtures, like copper sulfates, can be spread across roofs as a powder to prevent algae from returning. Ask your cleaners if they have a similar product that they can use when they wash your roof.
  • Replace Your Roof with Algae Resistant Shingles. If your roof is getting close to the end of its lifespan, you may want to save your money and instead hire a roofer to install some new algae resistant shingles instead. These products are covered with small granules of copper that have the same preventative power of copper flashing.

Algae, you’ve finally met your match!