What causes black straks on my Roof

What causes these black streaks on my roof?

Many people believe that the cause of the dark colorations on the roof come from jet airplanes bombarding their roof with toxic jet fuel. This is simply not true. The black coloration actually comes from photosynthetic cyanobacteria consisting of algae spores known as Gloeocapsa Magma. It feeds off of the limestone used to make both asphalt shingles and concrete roof tiles. These spores thrive in wet conditions and humid climates. This is one of the reasons that it is more prevalent on the north and west sides of the roof. These areas tend to be wet longer in the morning which allows the spores to thrive. There is no scientific proof that these spores have any major impact on your health although this is commonly advertised from roof cleaning companies. Some have gone as far as scare tactics. This is not necessary. It is however proven that the spores can absorb heat and reduce the ability of your roof to reflect the sun’s rays. The effect can cause your attic to absorb more heat and raise your electricity bill from you’re air conditioner working harder to keep your home cool. They can also have major effects on tarpaper and wood shingle surfaces. If left untreated the spores can retain more moisture and as they grow can start to breed lichens. They can root into the surfaces often causing granular loss to asphalt shingles or wood rot to cedar shake shingles. Finally most Home Owners Associations have strict rules on roof cleaning. On average they only allow a homeowner a maximum of three years between cleanings.