Q & A - Why Does Moss Grow on Rooftops?

Will moss damage my roof?

Yes, it can.  Moss forms on a roof when it is wet or constantly damp and shaded. It occurs most of the time on the north side of homes in the northern hemisphere but can develop anywhere the roof that doesn’t get sunlight. Moss can develop from algae spores blowing from the wind or even as simple as a bird carrying a twig for making a nest and it drops a spore on the fertile roof.

As moss grows on your roof it can actually work its way under your shingles. The moss, because it is a plant, can literally push up the asphalt shingles as it grows and can cause them to become detached which makes them susceptible to blowing off in high winds. Moss is also a real unpleasant look for your roof. Selling a home with moss can give an impression of a worn-out roof to a buyer.

What can I do to get rid of the moss from my roof?

First of all, remember the roof is steep and with the moss it is very slippery to walk on. Note cedar shakes are by far the most dangerous to walk on with moss. It is advised to use a licensed roofing contractor to clean the roof. There are specialists that do just this type of work. I strongly advise using a professional for this project.

Is there anything to keep moss from growing on my roof?

It is very customary in Europe to install copper near the top of a roof to keep moss from growing. A little investigation of this proved to me that this was true. When rainwater and copper touch, it precipitates a fluid that kills the moss or at least retards the growth. The moss just hates it. This picture is of a job I contracted. Using the copper at the ridge line helps keep the moss under control.

There are shingle manufacturers that now claim resistance to algae discoloration on the shingle for the same reason. They have embedded in their shingle mat tiny zinc chips that react the same as the copper does. Zinc Strips about four feet long are also available to install on your roof and should be installed with zinc-coated nails.

Most of all, keeping the roof free of debris and trees pruned/trimmed back should help reduce moss growth on your roof. This will allow more sunlight to reach the surface of your roof helping it to stay dry and free of moss.

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