Most people don't pay much attention to roof cleanliness, but there are several roof cleaning problems that if left ignored can cause chaos on shingles, shakes and tiles. These issues could eventually lead to the decay of the roof's very structure. There are many things the average homeowner can do to notice signs of trouble and exterminate any potential problems. Black algae is usually found on shady spots of the roof and is often mistaken for mildew or fungus. Unlike the black streaks seen when asphalt shingled bleed-through, the staining of black algae is consistent. This stain is in actuality dead organic debris.
Shingles made of zinc or copper granules prevent algal growth, but a simple way to avoid black algae growth is by cutting overhanging tree branches by the affected area of the roof to let more sunlight through. There is also zinc or copper strips designed to be attached to the ridge so when it rains algae-killing metal salts will wash down the roof. Pressure-washing the algae is another option but can be adverse to shingle integrity. There are numerous types of chemical remedies to solve this problem, however it is best to contact a professional roofing contractor to help come to the best decision.
Debris staining is another fairly common problem, and has the most effect on low pitched roofs with overhanging tree branches. This occurs when piles of debris, for instance leaves or pine needles collect on the roof. The debris retains water and can cause critical damage if left unchecked. Algae and fungus can form here, but even actual plants may start growing. Plants that grow too large will produce elaborate and destructive root systems that move into the roof structure. Moss, lichens and other plant life are often able to survive on a neglected roof, so the most effective method to prevent this problem is to physically remove debris by sweeping the rood. Take care not to damage any roof materials, such as shingles.
If black stains appear on your roof in the shape of streaks, you more than likely have a "bleed through". When the material in asphalt shingles begins to break down it bleeds from the shingles and causes black streaking. On the down side this is most often a sign of faulty materials. It can be difficult to differentiate between bleed-through and black algae, which is why it is important to get the advice of a reputable roofing contractor before deciding on a solution.