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Can Moss and Algae Hurt My Roof?

How can Moss and Algae Hurt my Roof?

Mold, mildew and moss not only look unsightly on a rooftop, they can deteriorate roofing shingles, causing them to lift and allow water to enter your home. Because of the potential for moisture problems, both moss and algae can shorten the lifespan of your roof if you don’t keep it clean of these damaging organisms.

How Algae Can Lead to Roof Damage

What is known as blue-green algae appears as black streaks on your roof, which hurts the appearance of your home. Since certain types of algae only discolor roofing shingles at first, you might not realize you have a problem until the algae turn black.

If you live in a region where the humidity is high, algae — more commonly known as mold and mildew — might accumulate on your roof, especially on areas that are shaded. If not removed, this mold and mildew on roofing shingles turns black and holds moisture from rain, snow and ice. Trees hanging over the roof creating shady spots can make the problem worse.

Algae can grow anywhere on your roof, but it normally grows on the side of the roof that faces to the north. The lack of direct sunlight on areas of the roof — generally on the north side — leads to the accumulation of moisture that the sun doesn’t dry up. Rain and morning dew, in particular, evaporate more slowly on areas of the roof that don’t get a lot of light from the sun.

The crushed limestone that is used to bind asphalt and fiberglass together on roofing shingles provides food for algae. Algae, which are simple plants, will continue to grow until you or a professional roof cleaning company removes the algae by killing it with the use of a fungicide or biocide.

Moss Keeps Roofing Shingles Damp, Eventually Eroding Them

Why Moss Is an Enemy to Your Roof

When mold and mildew aren’t removed and are left to build up on a roof, moss — a thick, green spongy material — can develop. Like algae, moss thrives in a humid environment as it needs water to grow. When moss isn’t removed, it keeps roofing shingles damp, allowing moisture to rot the shingles.

Although moss grows slowly, it feeds on components of asphalt shingles. As the roots of the moss implant themselves into the roof, they begin pulling on the granules that coat asphalt roofing shingles. As shingles lose granules, they become less resistant to adverse weather conditions. Also, with the moss roots pulling on the shingles, they can eventually loosen and allow water to leak into the house.

How a Roof Cleaner Can Help

While it might be necessary to clean your roof annually to control the growth of algae and moss, professional roof cleaners often use a low pressure spray that won’t damage roofing shingles. If you’re worried about the use of chemicals, the roof cleaner will either use cleaning products that are not harmful to the environment, or will take the steps necessary to protect shrubbery, flowering plants and your lawn from any cleaning chemicals that run off the roof.

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