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Why it’s Important to Keep your Roof Clean

Published on Thursday September 28, 2017

Roof cleaning tips.

When the siding on the exterior of your home is dirty, or the paint is peeling, it makes your entire house look dingy.

As homeowners, we know we’re expected to keep our homes looking nice — no one wants to come home to a mess, and no one wants to own the house that the neighbors grumble about whenever they drive past. That includes your roof.

Not only can a dirty roof ruin your home’s curb appeal, but it can actually damage your roof. That’s why it’s important to keep your roof clean.

More than Dirt

Your roof is exposed to the elements all day, every day. Dirt and debris will collect on it. Natural rainfall is typically enough to wash off the appearance of most dirt. However, the dark stains and green areas that appear on your roof are caused by other natural elements:

  • Algae
  • Fungus/Lichen
  • Moss

These substances are much trickier than simple dirt and require some explanation.


Black stains are called gloeocapsa magma or GM. GM algae is a bacterium that feeds off of both asphalt and limestone roofing in moist, cool and shaded areas of the roof. When there is minimal light, GM forms a blue-green color.

The more shaded areas of the roof are more likely to have these algae, which can harbor various types of molds. This explains why some roofs are stained only on one side.

A report by the Asphalt Roofing Manufacturing Association (ARMA) notes that these algae spores are transported by wind or animals. They can quickly spread from rooftop to rooftop in neighborhoods of single family homes, townhomes and apartment complexes.


Lichens are basically the combination of algae and fungus. ARMA describes lichens as fungus that grow symbiotically with algae.

These plant-like organisms form a branching growth of “root-like tentacles that penetrate deep into the shingle’s organic, oil base for nourishment.” Lichens are tough to remove from the roof and can reappear from humidity and rain.


Moss on roof.

Unlike the algae and lichens, moss is an actual plant. Moss has a shallow root system and requires a lot of moisture to survive. Areas with less sunlight remain damp longer.

Overhanging tree branches not only provide more shade, but they also drop debris that serves as a food source for moss. Like algae, moss spores are often transferred by wind or animals and can easily spread throughout neighborhoods.

How Can Stains Damage a Roof?

The stains and growth patches caused by algae, fungus and moss can damage your roof through shingle deterioration and wood rot. Both lead to expensive repairs and can shorten the life of your roof. A roof cleaning can help minimize or eliminate this damage.

Shingle Damage

As mentioned above, GM algae is a bacterium that feeds off of both asphalt and limestone. That means that these organisms are literally eating away at your shingles.

Furthermore, according to ARMA, roofs with algae stains absorb heat. This results in an extremely high heat in the attic, which can reduce the lifespan of the shingles by essentially baking them from the inside out.

Lichen colonies can be quite damaging to shingles. The penetrating tentacles create pock marks where they grow and eventually ruin the shingles.

Moss is even more detrimental to roof shingles. Moss can cause the edges of the shingles to lift or curl—often the first sign that a roof replacement is needed. And because moss holds in moisture, it can freeze in the winter, causing even more shingle damage.

Wood Rot

Wood rot on roof.

Moss has the ability to hold in moisture and divert water, which makes your roof deck susceptible to wood rot and leaks. Moss tends to grow in the slots between shingles, which is the last place water evaporates from a roof.

Moss growth on your roof is easy to spot. But the signs of wood rot are not always obvious to the average homeowner. “You don’t know how much damage is done to your house,” says Yanni Avramidis, vice president of production for Long Roofing.

“You may have a leak and you don’t even know it. This will cause even more wood damage.”

Wood rot not only shortens the life of your roof, it can cause mold growth, which can be hazardous to homeowners and their pets.  

Do you have guests in your attic or on your roof? Unwanted critters can cause more damage when the wood begins to rot.

Animals, such as squirrels, have been known to cause roof and attic damage by chewing through areas of the roof and supporting wood systems. Rotted wood makes it easier for these creatures to bore through.

Professional Cleaning

Roof cleaning professionals.

Roof cleaning not only maintains a beautiful appearance, it protects your investment by extending the life of the roof. While it is tempting to make roof cleaning a DIY project, it is recommended to hire a professional roof cleaning company.

Standard, high-pressure washers can damage your roof when you’re trying to clean it. It’s important to use special equipment that does not harm the shingles and cause them to be torn from the high pressure.

Reputable roof cleaning companies will also use a biodegradable cleaning solution. A DIY roof cleaning project typically uses a solution of water and bleach. While that can help rid the roof of algae, it is harmful to plants and the environment.

Preventing Future Growth

Once the stains are removed, you can take steps to prevent regrowth sooner. ARMA notes the biodegradable chemical cleaner can ward off growths indefinitely if reapplied every 18 to 36 months.

ARMA also recommends steps that can be taken to discourage moss and algae growth including:

  • Trimming tree branches
  • Clearing off existing debris that has accumulated on the roof
  • Ensuring your roof had proper airflow to avoid driving debris under shingle edges
  • Cleaning your gutters regularly

When Cleaning Is Not Enough

In some cases, the algae, fungus or moss growth is so severe that it has already caused significant damage to your roof. At this point, roof cleaning is not enough.

Angi advises that, “If you are missing shingles, your shingles are more than 25 years old, there are no granules left on your shingles, tabs are flipping up or if the shingles are brittle, then yes, you likely need a roof replacement.”

Has Algae, Moss or Fungus Damaged Your Roof?

If you think your roof may need to be replaced due to damage caused by algae, moss or fungus, contact Long Roofing online.

A licensed professional will come to your home for a free, no obligation assessment to replace your old roof with a beautiful new roof with a 50-year warranty.   

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*Excludes labor. Subject to credit approval.

**Excludes labor. Subject to credit approval.

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