What to Do About the Algae on Your Asphalt Roof

One of the unfortunate facts of living in a high-humidity environment – especially ones hit with constant storms – is the threat of algae growing almost everywhere. A particularly common strain of algae called Gloeocapsa Magma can collect on asphalt roof tiles as airborne spores, leading to unsightly dark stains. While shingles coated with zinc and copper granules inhibit the growth of these spores, some asphalt shingles don’t have this feature and easily become a spawning ground for algae. While the experts at Horisons can always assist, here are some steps you can follow to rid your home of this infestation and have a sparkling clean roof again.

Ingredients you’ll need:

  • A cleaner (whether a professional algae remover or a solution of 50% water 50% bleach, although keep in mind multiple washes with harsh chemicals can damage shingles)
  • A pump sprayer
  • Garden hose with a spray nozzle
  • Safety goggles
  • Rubber gloves
  • Safety rope (a reliable way to keep yourself from falling while you work)
  • Old expendable clothes
  • Ladder
  • Slip-resistant shoes

Remember to always be cautious when working on a roof. Avoid working and stepping on wet surfaces. We recommend cleaning your roof in overcast weather as this will prevent your cleaning chemicals from evaporating. Water any plants beneath your roof before you clean as well to protect them from the chemicals that will spill over the edge.

The cleaning procedure is as simple as pumping the cleaning mixture onto a section of the roof, letting it sit for 15 minutes, and then rinsing it off with your garden hose. We recommend working a section at a time to give yourself space to work.


To keep your roof algae-free in the future, the best thing you can do is install a strip of copper or zinc-coated sheet metal along the ridge of your roof. Horisons can assist in this regard as well. These metals inhibit algae growth, and whenever it rains, molecules of metal will wash down your roof, killing any spores that would normally grow.

From leaks in your roof to complete roof or siding renovations, the professionals at Horisons are ready to help you today. Contact us online a free quote, consultation, or inspection or give us a call at 713-782-7663. 

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