Recently I was asked what is going on with asphalt roofs. They appear streaked with black and growing things on them. Here is my response.
In the late 70's-early 80's we had a petroleum shortage here in the U.S. Long gas lines,odd and even license plates determining when you could buy fuel etc. At that time asphalt shingle manufacturers were having trouble getting petroleum to use in their products, asphalt shingle. They had to come up with a new formula for their product so they added fillers to take the place of the missing petroleum. They added limestone dust to the base and coated with small amounts of asphalt. Calcium Carbonate,a food product was also introduced and used in shingle manufacturing. These fillers seemed like a good plan at the time.
The problem with using these fillers they learned a few years later is they are food for algae,moss and lichen. All these organisms slowly eat away at the shingles seeking more food. The Shingle manufactures first noticed the flaw in their plan on roofs in the lower states. The higher humidity increased the growth dramatically. The manufactures had to come up with a plan for cleaning their product without voiding their own warranty. This method gave birth to the asphalt roof cleaning industry.
Call it climate change,global warming, whatever, but the fact is it is more humid in the northern states now then it was 20-30 years ago, enabling the spread of the algae to flourish on roofs throughout the U.S.
After all these years of complaints and lawsuits the Shingle manufacturers are once again changing the formula for their product. Rather then go back to the old formula they've decided to just add another mineral to the existing formula. The outcome of the new formula is still unknown.
by Sussex County Roof Cleaning