How To Address The "Growing" Problems On Your Roof

Here are some facts, myths, and solutions addressing the “growing” problems on roofs caused by algae, lichen, fungus, and moss. Here are some facts to get us started:

  • Algae, or Gloeocapsa Magma, can spread from one infected roof to another via the release of airborne spores. As more homes are built closer together, this hardy algae has been able to spread rapidly.
  • Algae is well adapted to extreme conditions. Heat, long dry spells, UV rays, heavy rain, intense cold, thick snow, or high winds won’t deter it.
  • Algae can go for long periods of time without water. It is unaffected by heat or downpours and is dormant in winter. Algae secrete a material that adheres them firmly to the shingle surface.
  • The dark color of Algae is a pigmented protective sheath which encapsulates each cell to protect it from UV rays
  • Copper and Zinc can both inhibit algae growth. Zinc (including pellets), however, has other inherent problems such as it’s limited ability to be color-matched to roofing shingles, attachment method to roofing shingles, cost, and the occasional “bloom” effect due to the build-up of zinc oxide. Copper granules are used instead of zinc for these reasons.
  • Copper is 10 times more effective against algae than Zinc. Zinc actually becomes less effective against algae quicker than copper
  • AR shingles at work. Some granules covering the shingle contain copper encapsulated by a specially developed coating allowing the copper (cupric ions) to be time-released to prevent algae over a long period
  • Dew is the dominant source of water for algae and is the “agent” best suited for the release of the copper in Algae Resistant shingles. Rainwater, although effective, runs off a roof too quickly to provide significant leaching of copper. Dew is also present more days than rain.

Myth vs Fact

Myth 1: Algae is killed immediately by copper.

FACT: Algae cells are poisoned over time.

Myth 2: Algae is a fungus.

FACT: Algae, or Gloeocapsa Magma, belongs to the Cyanobacteria branch in the Eubacteria family and is not a fungus.

Myth 3: Installing a copper ridge or hip shingle with copper granules on an existing roof may overcome an existing colony of algae.

FACT: AR granules have not been proven to kill existing algae.

Myth 4: Fungus Resistant (FR) shingles are better.

FACT: “FR” is an inaccurate name since fungus is not the actual source of the suggested problem. Additionally, copper granules have not been proven to inhibit fungus growth.

Questions Answered

What Does it Look Like?

  • Dark/black or green stains or streaks on roof, also called “Blue-Green Algae” (Cyanobacteria) and “Gloeocapsa Magma”
  • Green, connecting colonies; includes mold & mildew
  • Green, spongy clumps can be random growths.
  • Orange, White, or Yellowish spots in a starburst shape

What’s Needed for Growth? 

  • Moisture, inorganic food sources (asphalt fillers), airborne spores, proper temperature
  • Moisture, organic food sources (soil), spores, proper temperature – 40 F to 100F

Where Does it Grow?

  • Nationwide; 80% +/-.
  • Mostly Southeast coastal and Pacific Northwest. 
  • High humidity, heavy shade, any exposure.
  • Heavy and/or low tree coverage aids growth.

What is the Typical Roof Exposure?

  • Mainly North-facing but can occur on all exposures.
  • Any exposure.
  • Heavy and/or low tree coverage aids growth.

What is the Impact on my Roof?

  • Aesthetics
  • Poor drainage
  • Slippery
  • Potential to lift shingles
  • Possible premature deterioration

Are Algae Resistant Shingles Effective?

  • Yes and No. It may inhibit growth in early stages only, but will not prevent growth.

How Do You Get Rid Of It?

  • Wash the roof shingles with an “Anti-Algae Solution”*. Apply at low pressure, wait 15 min. rinse with low-pressure water. Protect plants/shrubs. Do not power wash. Use Fall Protection.
  • Remove the initial bulk of growth with a stiff brush or broom. Then treat the roof as you would for algae.

*Anti-Algae Solution: 4 Gallons of water, 1 Gallon of bleach, 1 Cup of Tri-Sodium Phosphate (TSP).

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