You might have recently noticed a black discoloration on some areas of your roof and assumed that this is mold or mildew. However, this is more likely to be moss or algae growth, and it can cause damage to your home if left untreated.
How Moss and Algae Can Damage Your Roof
Although both look similar, moss and algae are very different from each other. This means they require different procedures in cleaning and preventing them from growing on your roof. Typically, algae grow when moisture forms on roof surfaces, which often happens in coastal or humid climates. Some types of algae are even immune to ultraviolet (UV) rays by producing a dark pigment that you may see as streaks on the surface of your roof.
Moss, on the other hand, is a non-vascular plant that obtains water through its leaves. They thrive in a moist environment to survive, so they tend to grow on roofs that face north because that area receives little and indirect sunlight. Shade from nearby trees can also allow it to grow on other parts of your roof, and moss spores can be carried by small animals or the wind to neighboring roofs.
Cleaning Moss and Algae
Roof cleaning can be tedious and dangerous if you don’t have the right equipment, so be sure to hire a professional to do the job for you. Otherwise, you can try the most common method of mixing equal parts laundry strength chlorine bleach and water, and apply it on the affected area with a sprayer. Make sure to allow the solution to saturate the surface for about 20 minutes before rinsing it thoroughly with low-pressure water. Algae should be able to disappear and wash away with subsequent rains while moss will loosen over time until it can be removed with a leaf blower.
To prevent moss and algae from growing on your roof, you need to trim any overhanging branches that may block the sunlight. This will not only minimize debris on your roof, but also prevent moss and algae from growing. You’ll also need to clean your gutters regularly to allow the water runoff to drain smoothly and prevent water pooling.