How and Why Moss Grows and Damages Your Roof

Moss growth on your roof is a serious concern. Left unattended, moss can spread and cause all kinds of damage. While moss is the most common form of growth on your roof, homeowners should also be aware of the spread of algae and lichen, as well as the buildup of organic matter–such as fallen leaves, twigs, branches and nuts–which will support the buildup of moss.

Just how does moss grow on your roof? Let’s look first at just what might be up there growing, and then we’ll examine why it needs to be taken care of.

What Are Moss, Algae and Lichens Anyway?

Moss, algae and lichens are all different types of growth that can be found on your roof. Each of them can damage your roof in various ways. But while most people simply see growth on their roof and assume it’s all the same, the truth is that there are subtle differences between them.

Moss is a bryophyte that develops from water-based plants. A carpet of moss is generally springy to the touch, with short tendrils shooting upwards. While moss requires water to grow, it cannot grow immersed in water.

Algae is a thallophyte and grows in water. It has no root, stem or leaves. Algae are single-celled plants that grow in clusters.

Lichen is a combination of algae and fungi. Lichen is not technically a plant at all, but rather a type of fungus that exists in a symbiotic relationship with algae. There are four types of lichen with varying appearances, and it is easy to mistake lichen for moss.

Why Does Moss Grow on My Roof?

Moss, algae and lichen grow on your roof through a combination of two things: moisture and organic debris. The more water and the more debris, the greater the chance of moss growth. Another critical factor is the amount of shade your roof receives. A well-shaded roof prevents the evaporation of moisture, creating excellent conditions for moss to thrive.

Moss and algae can often be spotted from the ground, but most roofs can actually support moss growth that can remain unseen for long periods of time. This is because moisture gets under your shingles and allows moss to grow out of the light of the sun. For this reason, evaluating moss growth on your roof takes more than just glancing up and taking a look.

How Moss Damages Shingles

Moss damages your shingles in three significant ways.

First, moss will strip away the protective oils on your shingles, making them susceptible to erosion and sun damage. Without any protection, your shingles will warp and crack in the sun, significantly shortening their lifespan.

Second, moss absorbs water. So every time it rains, the moss sucks up more moisture and spreads farther across your shingles, eating away at this outer protective layer. If ignored, this moisture buildup will ruin your shingles, and you will eventually need to replace your roof.

Finally, moss spreads beneath your shingles. This moss absorbs water and thus allows moisture to invade into the interior of your home. When moisture builds up on the inside of your home, it leads to wood rot. This is the worst case scenario because it can mean far more extensive (and far more costly) repairs to your home.

How to Prevent Moss Growth

Now that you have a better understanding of how moss grows on your roof, the next question is how can you prevent moss from growing in the first place. Homeowners can take two approaches to prevent moss growth.

First, keep your roof clean. Removing buildup and debris on your roof goes a long way in ensuring that moss, algae and lichen have less of a chance of spreading. At least twice a year, be sure to clean out your gutters and downspouts. Remove fallen leaves, twigs, and branches from your roof. Look for punctures, broken shingles or tiles, and other kinds of damage that might allow in moisture. Patch all damage properly.

Second, hire a professional roof cleaning service to remove moss and algae buildup. A professional roof cleaner has specialized equipment that will remove all the grime, dirt, stains, moss and algae from your roof, and industrial cleaners that are environmentally friendly but will kill moss and algae down to the root. This kind of cleaning both removes restores the original luster of your roof and increases its longevity.