Does Algae Damage Roof Shingles?

August 15, 2023

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roof algae

If you've noticed dark green or black spots on your roof, you may be dealing with an algae problem. Algae is a plant-like organism that grows in moist environments, and roofs provide ideal conditions for algal growth. 

The question is, does algae damage roof shingles or is it just an aesthetic issue? Algae itself does not directly damage most roofing materials, but over time, excessive algal growth can accelerate degradation and deterioration by trapping moisture against roof surfaces. So while the algae alone is not immediately damaging, the moisture retention and staining caused by algal growth can contribute to roof damage long-term if the growth is not controlled.

What Causes Algae to Grow on Roofs?

Several factors contribute to algal growth on roofs:

  • Moisture - Algae needs a damp environment to survive. When dew, rainwater, or snowmelt lingers on your roof, it creates a moist environment for algae. Areas that don't get much sun are especially prone to algae.
  • Temperature - Algae thrives in warmer temperatures. Roofs heat up in the sun, making them an ideal home for algae.
  • Nutrients - Algae gets its nutrients from dirt, dust, bird droppings, and other debris that collect on your roof. These materials provide food for algae.
  • Roof Material - Some types of roofing, like asphalt shingles, are more prone to algae growth because they absorb and retain moisture.

The Big Question: Does Algae Damage Roof Shingles?

The algae itself does not directly damage asphalt or composite shingle roofs if not removed from the roof. However, over time algae can contribute to the degradation of the roof in a few ways:

  • Retains moisture - The algae mats retain moisture on the roof surface. This excessive moisture can lead to loss of granules on asphalt shingles and damage the protective mat on composite shingles.
  • Growth underneath shingles - Algae hyphae (root-like filaments) can grow underneath shingles, causing deformation or detachment.
  • Erodes surface - As algae grows and spreads, it can slowly erode the mineral surface layer of asphalt shingles.
  • Stains - The pigments in algae can stain shingles, decreasing overall reflectivity and leading to increased temperatures.

So while algae alone will not directly cause leaks or roof failure, if left unchecked it can accelerate normal weathering and degradation of shingles.

does algae damage roof shingles

Will Algae Hurt Other Roof Types?

Algae is less likely to damage other roof types like metal, tile, or slate. However, if the growth is extensive, it can still cause problems:

  • Retains moisture - Just like on asphalt shingles, thick algae mats hold moisture against metal and tile roofs, which can lead to corrosion and deterioration.
  • Clogs drainage - Buildup of algae in roof gutters and drains can impede proper drainage, leading to moisture issues.
  • Aesthetic issues - All roof types can suffer from unsightly black stains from algal pigments. This is mainly an aesthetic problem.

So while algae itself won't compromise the integrity of these materials, heavy growth can contribute to moisture issues that speed up deterioration over time.

Options for Removing Algae from Roofs

If your roof is suffering from an algae problem, here are some ways to remove and control it:

  • Pressure washing - Power washing using a pressure washer with a roof cleaning attachment can blast away algae and debris from the roof. Take care not to damage shingles.
  • Chlorine bleach - Using a dilute bleach solution to kill algae is effective. Rinse thoroughly. Don't use bleach on metal roofs.
  • Algaecide products - Roof cleaners containing algaecides like zinc sulfate, copper sulfate, or sodium hypochlorite can help remove and prevent regrowth.
  • Ridge venting - Improving air circulation under the roof with ridge vents can help control moisture and algae growth.
  • Roof coatings - Applying reflective roof coatings after cleaning can inhibit algal regrowth. Look for algae-resistant coatings.

Prevent Algae Growth by Limiting Moisture

The key to controlling roof algae long term is limiting moisture. Here are some tips:

  • Clear debris like leaves from gutters and drains so water flows off the roof properly.
  • Trim back overhanging tree branches to reduce shade and moisture-trapping debris.
  • Ensure bathroom and kitchen vents aren't venting moisture into the attic space.
  • Install ridge and soffit ventilation to improve air circulation.
  • Repair any roof leaks promptly to avoid wet conditions.
  • Consider preventative algaecide treatment if your roof is highly prone to algae.

Following good roof maintenance practices is the best way to stop algae in its tracks and keep your shingles looking their best.

roof cleaning


While algae alone won't cause immediate roof failure, extensive growth over time can accelerate wear and tear on asphalt and composite shingle roofs. Keeping your roof clean, dry, and well-ventilated is key to preventing algae from taking hold and potentially contributing to costly roof damage down the road. With proper maintenance and cleaning, algae doesn't have to be a roof's worst enemy.

About Largo Pressure Washing Services

With over 20 years of experience, you can count on Largo Pressure Washing Services to clean your home and business exteriors right the first time. The team uses a combination of truck-mounted equipment and eco-friendly soaps for a job well done. Please call (727) 758-2424 to schedule an appointment.


Should you clean algae off roof?

Algae should be cleaned off roofs to prevent long-term damage. Although algae alone won't directly cause leaks or failure, over time it can accelerate wear by trapping moisture against shingles. Thick layers of algae can also clog gutters and drains, leading to other moisture issues. Using pressure washing, bleach solutions, algaecides or other cleaning methods can remove algae and prevent continued growth that could eventually contribute to roof deterioration.

Do algae stains affect the life of shingles?

Algae stains can potentially decrease the lifespan of certain roof shingles. The pigments in algae can cause dark stains on asphalt shingles, reducing their overall reflectivity. This causes the shingles to absorb more heat from the sun and leads to faster deterioration of the mineral surface layer. While algal stains alone won't directly damage shingle integrity, the increased temperatures contribute to faster weathering, granule loss, and breakdown of the protective mat over time.

How long do algae-resistant shingles last?

Algae-resistant shingles are formulated to inhibit algal growth and last just as long as standard asphalt shingles. Manufacturers claim algae resistant shingles have a useful life of 20-25 years under normal conditions when properly installed. However, just like standard asphalt shingles, factors like roof ventilation, weather, and sun exposure will determine actual lifespan. While algae resistance may help the shingles better maintain their appearance over time, it does not significantly impact the underlying durability of the shingle materials themselves.

Do Algae on roofs decrease property value?

Extensive algae growth on a roof can potentially decrease a home's property value. Algae stains result in an unattractive black discoloration that is visible from the curb. This unsightly appearance may turn off potential buyers and lower perceived home value. However, algae presence alone is unlikely to significantly impact value if it is just a cosmetic issue that can be remedied with cleaning and maintenance prior to sale. As long as the algae has not led to any major damage, its effect on value is mostly aesthetic.

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