Why Moss Is Growing On Your Steel Roof & What You Can Do About It

Metal roofs are highly functional and extremely durable, but that doesn't mean that they are not susceptible to damage from moss. Some people falsely believe that moss cannot grow on metal roofing, but moss can grow on steel. As with anything in life, the best way to solve a problem is to know why it happened in the first place. Here are a few frequently asked questions about moss on steel roofs, along with a few tips for how to get rid of it.

Why is moss growing on your roof?

Moss spores are tiny enough to get carried up to the roof by the wind. Spores can also hitch rides on animals and birds or drop from nearby tree branches where it may be growing. Moss does not have roots, but it does need something organic to grow on. Without an organic material on your roof the moss would not be able to "stick" long enough to grow. In other words, it would wash off of the roof the next time it rains.

The organic material that may be on your roof could be anything, such as pollen from nearby trees or droppings from birds. When these types of materials are on the roof, moss spores can easily attach to them and begin to grow while feeding off of the nutrients it gets from the organic substance.

Why is there more moss on one side of the roof?

Moss thrives in shady and moist environments. That is why your most northern-facing roofing structure may have more moss than the other sides. Sunlight can actually destroy moss and keep it from growing. This is also why moss tends to grow on houses that are built deep within the woods where little-to-no sunshine is able to reach the roof.

What kind of damage can moss do to steel roofing?  

Moss can damage any type of roofing material simply because moisture tends to get locked into the mushiness of moss. It becomes like a sponge and holds onto water every time it rains. With moss growing in sections on your roofing, it can cause the roofing to become discolored from staining and/or fading.

Over a period of time, the moisture can cause your steel roof to corrode, especially if the protective zinc coating isn't working anymore and it's allowing moss to grow on your roof. The moisture-soaked moss could become heavy, which can be problematic if the roof corrodes extensively. Of course, this is a worst-case scenario, but it's important to be aware of the possibility so you can prevent it from happening to your roof.

Corrosion, staining, and fading can be repaired. Of course, the moss growth would need to be removed from the roof first in order for a roofing contractor to be able to fully assess the damage caused by the moss. Therefore, hire a metal roof repair contractor to remove the moss from the roof and ask him or her to inspect the roof after the moss removal is completed.

Why isn't the protective coating working anymore?

When the metal was manufactured it was covered with a protective coating of zinc. The reason zinc is used in this type of treatment is because it is known to kill moss. Just as with many other types of protective coatings for a wide range of building materials, the zinc coating will not last forever. If moss is growing on your roof, it would be a good time to call a metal roofing repair service to schedule the removal of the moss followed by the application of another protective coating of zinc. 


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