When you discover ugly, dark-green or black streaks on your roof, you might be stymied as to the cause. Usually, the presence of green or black growth on the roof means that you have algae or moss growing. Algae and moss are different types of plants, but they can have the same effect -- staining the roof and reducing the overall lifespan of your roof, especially if your roof is designed to be highly reflective. Here's what you need to know about algae and moss growth on your roof and what you can do to prevent it.
What causes moss and algae growth?
Algae grows best on roofs when the roof itself remains moist -- usually because the roof is shaded or because the house itself is located in a humid environment. Coastal homes or homes in the humid south are particularly susceptible to roof algae growth. Spores come to rest on the house (they are carried through the air and are more common in moist climates as it is), and if the roof is not cleaned well, the algae flourishes. Once it is established enough to create visible discoloration, it is likely the algae has been present for several months.
Moss is slightly different. It also begins with spores, but it prefers shaded places on the roof with plenty of moisture for the moss's surface. This means you're more likely to find moss on sides of the house that collect rain water and dry out slowly after storms. Trees can also provide a steady drip of moisture onto moss as it grows. Falling leaves, sap, and other carbon-based debris provide ample food for growing moss. Over time, moss will lift shingles or curl them back, leading to premature roof failure.
What can you do to prevent moss and algae growth?
- Stay on top of cleaning your gutters. Clean gutters are important for preventing algae and moss growth. If your gutters are clogged, the water inside them keeps the neighboring shingles moist, making it a perfect place for a moss or algae to thrive. Keeping gutters clean also keeps water from collecting too much on the roof itself -- roofs without working gutters will drain less quickly, giving moss and algae plenty of needed moisture before the roof dries. If you have roofs with two elevations, make sure each section drains independently -- your upper roof should not pour onto the lower roof before reaching the gutter. The place where the water flows from an upper level will have trouble drying fast enough.
- Trim trees. Branches that hang over and shade the roof are especially concerning. Remove trees that hang over your roof, or call a tree service to cut the branches back. They not only foster the moist environment needed to grow moss and algae, but they are also a safety hazard during storms and winter weather. Do not try to remove the trees yourself, as you can harm the tree if you are not experienced in trimming and pruning. Direct, hot sunlight really helps to prevent algae and moss development.
- Remove collecting debris from the roof. Leaves can accumulate during the fall. These should be removed promptly, as they trap water on the roof.
- Have a roofing company remove some shingles and install copper or zinc strips to repel algae before replacing the shingles. Copper and zinc naturally repel algae.
You can carefully inspect your roof and gutters each year for signs of plant growth. If you do notice moss or algae, it's best to remove it as soon as possible to preserve your roof's aesthetics and prevent any damage. For professional assistance with cleaning your gutters, contact a company like Mr.Gutter, LLC.