Black streaks or black roof stains on asphalt shingles are caused by a hardy type of airborne algae called Gloeocapso Magma but is simply known as roof algae. It usually first appears on the north facing roof sloproof suffering from roof algaees where moisture and shade are most prevalent.
The algae lands on your roof and feeds on the nutrients in the shingles. As it rains the algae is spread down the shingle roof causing unsightly black stains that dimish the home’s curb appeal and resale value. Most people are not aware what these black streaks are and that they can be cleaned. Too many people will consult with a roofing contractor and decide upon a complete roof replacement whether they were mislead by the contractor or the contractor was uneducated about roof algae as well. It is a fact that 50% of the roofs that are replaced in the Midwest are replaced due to their appearance and not their functionality. Replacing a roof that only needs cleaned is like replacing vinyl siding because it develops mildew, it doesn’t make much sense, yet many homeowners end up spending thousands of dollars to a replace a roof that only needed cleaned.
Some roofing contractors may not provide you with accurate information. Some won’t be honest because obviously they want to make money replacing your roof, while others are simply uneducated about roof algae and cleaning shingles. Some roofing contractors think that black streaks are a sign of wear. Or they may tell you that roof cleaning will damage your shingles.
It is true that using too much pressure on your shingles can do more harm than good, you should never allow a pressure washer to be used on your roof. With that said, the major shingle manufacturers do recommend cleaning shingles suffering from roof algae using low pressure methods so no damage is done. They also have suggested roof cleaners and roof cleaning chemicals that should be used.low pressure roof cleaning restores appearance and home value
Not taking care of a roof suffering from roof algae will result in the algae taking over the entire roof. This algae will diminish the life of your roof, will increase your home cooling costs, and will deplete your home’s perceived value. Low pressure roof cleaning can save you thousands of dollars over a premature complete roof replacement. You may not get the whole truth by calling a roofing contractor, so first educate yourself and consider calling a roof cleaning company to come out and discuss a possible cheaper solution.