How to Keep Your Asphalt Shingles Free from Algae

Apr 12, 2017

How to Keep Your Asphalt Shingles Free from Algae

What Causes Algae to Grow on Shingles?

Algae growth is attributed to high moisture levels in humid areas of the country. The Southern, Northeastern, Southwestern and outermost Western regions of the U.S. are affected the most by high humidity and thus, algae. If your asphalt shingles are covered in a dark stain, it’s probably the Gloeocapsa Magma known for its blue-green hue. It develops when airborne spores land and settle in between the cracks of individual shingles where they can feed on rainwater and air moisture to help them grow.

How Bad Can It Get?

If you get lazy or decide to leave it alone, you’re taking a big risk as algae don't only take away from the roof’s aesthetic, it can be detrimental to how well it insulates your home. All asphalt shingles are coated with a thin layer of mineral granules to protect them from the sun’s light and UV rays and help them perform better at trapping or reflecting heat (whichever is more appropriate for a said region’s climate). Algae do two things here that can render asphalt shingles’ protective properties obsolete:

  1. Algae thrive on moisture or water as mentioned earlier, which means that there will always be pooling in the cracks, increasing the chances of water penetration into your home and undermining its structural durability.
  2. If your area sees snow and frost every year, the water trapped in algae will turn into frost and ‘freeze’ the shingles’ mineral granules, prompting them to break down and taking away from the shingle roof’s energy-efficient qualities.

The Best Way to Keep Your Shingles Algae-Free

Metal Flashing

One simple solution to keep algae from forming is to install metal flashing all around the roof peak’s perimeter (or just the base of a chimney or vent). The point is to let any water collected in the metal flashing’s crack to chemically react and flow down to kill the algae. So long as the metal flashing is coated with zinc or copper, the water running through the cracks from the top-down will make it too toxic for algae to grow. And will keep it that way.

Today, some roofing shingles are covered in tiny copper fragments to make the shingle itself resistant to algae attacks. If you live in a town or city with particularly high moisture levels, ask your contractor for this upgrade to bring the roof’s required rate of maintenance down to a minimum.

Cleaning with Chemicals

Cleaning your roof with a chemical solution and using a pressure washer to rinse it off will have an immediate effect on the cleanliness and look of your roof. However, regular cleaning using such harsh chemicals and pressure washing will damage it and take away from its longevity.

Chlorine or oxygen bleach cleaning products are good at killing algae and restoring your shingle roof’s appearance (more or less). Chlorine is definitely the most effective option and the most immediately apparent after a wash.

All in all, any method of cleaning you choose of these will work. But if you’re looking for a permanent solution, metal flashing is the way to go because it maintains your roof’s original look the longest, which means sustainable longevity, less maintenance work and costs, and ‘curb appeal’ for your home.

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