Many of the regions where roof tile is prevalent are susceptible to mildew and/or algae growth due the prevailing environmental conditions. Mildew is not analogous to roofing products as it can also form on any exterior surface including stucco, siding and driveways.

Mildew and algae do not grow directly on the roof tile. The amassing of dust and other organic materials that may settle on the surface of tile facilitates growth. When moisture and sunlight are present, spores will begin to grow. Many variables play a role in the growth of mildew, algae and moss such as the location of the structure, exposure to the sun, exposure to dew, surrounding trees and bodies of water. Environmental factors such as wind, changes in rain patterns and even animal activity will contribute to the accumulation of algae on a roof.

Mildew and algae growth can occur at any time during the life of the roof, and many factors will contribute to its presence, or reemergence on a previously cleaned roof. Man-made factors, including grading and excavation, tree trimming, CO2 emissions and even gutter cleaning can and will foster an environment where spores are released; promoting mildew and algae growth.

Don’t worry, there is something you can do, and you don’t necessarily need a new roof.  Most of the damage that mildew and algae does is completely superficial.  A roofing company will be able to come out and make sure your underlayment isn’t damaged and clean your roof with a water pressure cleaner.  According to Eagle roofing products who produce concrete roofing tiles, a pressure cleaner set at a maximum of 1200 psi should be used.  

If you decide to clean your roof yourself instead of hiring a professional, keep these 2 tips in mind.  

1) The tip of the nozzle on the pressure cleaner should be kept approximately 12 to 24 inches from the surface of the tile.Limiting the pressure and maintaining a safe distance from the surface of the tile is intended to prevent damaging the surface.

2) The addition of a mildew inhibiting solution should be limited to a 90% water, 10% solution ratio.

Roof tile manufacturers have no control over mildew or algae growth, but it can be easily removed or treated without compromising the integrity of the concrete tile.