Is Roof Moss Bad?

Yes, roof moss IS bad — and for many more reasons than you might have initially thought. That’s why you should never ignore it if you spot neighbor’s or other homes in the area suffering with the green problem. Instead, you should spring into action and get your own property roof inspected, just to make sure that the organism can’t become a problem for you.

Wind can carry the spores off moss from one roof to another, so it won’t take long for the green stuff to ‘jump’ from one building to the next. Wind isn’t the only thing responsible, however; wild animals and birds can easily carry the spores between the locations without realising it.

Moss will struggle to grow in areas where the sun hits and the temperatures are high, and that’s why you usually see North American homes with moss on just the northern-facing rooftops. The southern side gets a lot more sun, and any moisture is quickly dried up by the direct light and heat. The northern side, on the other hand, is cooler and retains moisture more, caused by reduced sunlight. You will commonly find roof moss in cool, damp areas — under tree branches or where trees/structures cause shadows, the cool area around the chimney, etc. Garden debris, such as leaves and branches, can get blown onto the roof with high winds or bad weather, and this can create cool spots that moss can thrive beneath. This is why it is important to remove mess and waste from the roof as soon as possible.

Finally, around the guttering is an area where moss flourishes, and it is important that you inspect and clean them as frequently as you need to, to allow them to work as they should. It takes the smallest buildup of moss and other waste to cause a very big problem, specifically with leaks, and it's not a risk that we advise taking.

Roof moss is bad for the roof because it can cause damage that, in some cases, could cause the need for a full roof replacement. It is possible to stop roof moss from growing, but it won’t happen with a one-off treatment that then allows you to kickback and relax. Just as your garden requires maintenance and repair every now and again, or your vehicle, so does the roof. Regular inspections, professional or otherwise, will ensure that you pick up on the start of moss growth, alongside a host of other problems. Leaks or standing water, for example, cause not just the growth of moss, but also black mold and other organisms that could prove costly to the health of those in the building. Stop the leaks and standing water and you’ll go some way to stopping the moss. That's not the only thing you can try, though.

You should also look at what might be causing damp or cool spots on your roof, such as the shadow of trees or their branches, the chimney stack, vents, etc. You will find that these cool spots are prime points for moss, especially if they’re on the north-facing side of the roof. Cutting back the trees is a fairly simple task, but you won’t be able to remove the chimney stack and place it in a better position. Instead, you could look at incorporating copper or zinc strips to the roof, so that rainy weather encourages a coating of the material lightly across the entire roof. This prevents the growth of both moss and algae, as well as various other problematic organisms. High-acidity products can also work well at discouraging moss and algae, but too much of the products left on the roof for too long a period of time could result in stained shingles and other materials. Products that are high in acidity could also cause corrosive activity on the roof. We don’t recommend attempting this without prior research and/or professional guidance.

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