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Shingles are manufactured with different degrees of quality. Most shingles installed by the builder are in the low to medium quality range with little, if any, fungus fighting elements like zinc or copper. Even on roofs with fungus resistant shingles the protection can begin to fail within a couple years. When the protection fails, airborne spores that settle on the shingles begin to grow and reveal themselves as an ugly black fungus.
These spores need three things to grow: moisture, heat and nutrients. Growth usually begins on the North side of the house because it’s normally the last part of the roof to dry after a rain or morning dew. The sun begins to heat up the shingles raising the humidity and creating the ideal environment for growth. The nutrients can be found within the shingles themselves. The asphalt used in making the shingles is the perfect food source because fungus lacks chlorophyll and is unable to manufacture food like other plants. The fungus secretes enzymes into the asphalt that digests the raw material which is then absorbed.
Because the asphalt at the granule base is consumed first, dislodging the granules that protect your home against UV radiation and insulate the roof against excessive heat, your 25-year roof will most likely last less than 15 years.
In addition, a roof covered with fungus will absorb more heat causing under roof temperatures to significantly increase making your A/C run longer!
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