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Can You Identify What’s Growing on Your Roof?

There are four types of growth to watch for:

  1. Algae
  2. Lichen
  3. Fungus
  4. Moss

Algae Growth

  • Extensive Algae growth – in both green and black.
  • Different colors are evident.
  • Dark appearance is a protective layer the algae have developed to protect itself from damaging UV rays.

Algae Growth

Algae, Lichen, Fungus

Algae, Lichen, Fungus

  • Evident in this image are Lichen, Fungus & algae.
  • Notice the vent metal has inhibited growth. This observation is what initially prompted researchers to finding metals which prevent algae growth.
  • Note the algae-free surface on dormer roof. This is due to exposure to the sun, allowing that portion of the roof to dry faster.

Algae Growth

  • Extensive algae growth.
  • The area below the window is free of algae due metal flashing… run-off of the metal inhibits growth and algae.
  • Algae predominantly grow from the bottom up, due in part to the amount of time water is on the roof.



Lichen & Fungus Growth

  • Fungus is predominantly at the shingle edges and keyways.
  • Left to grow may eventually damage the shingles by lifting them and further inhibiting water run-off.


  • Moss due partly to low slope, shady location, organic material & exposure.
  • Water is retained on the roof; thus essentially aiding the growth.
  • Organic material needs to be present for growth or moss cannot take root.


Geographical Predominance

  • White: Very Low Algae, Moss, Lichen and Fungus Growth
  • Yellow: Low Alga, Moss, Lichen and Fungus Growth
  • Red: Severe Algae, Moss, Lichen and Fungus Growth