Maintaining a healthy roof is crucial for the overall integrity and longevity of your home. One common issue that homeowners face is the growth of moss and algae on their roofs. These unwanted invaders not only affect the aesthetics of the roof but can also cause damage if left untreated. In this comprehensive guide, we will explore the causes of moss and algae growth, the impact they can have on your roof, and effective methods to handle them as part of your roof repairs.

Understanding Moss and Algae Growth

Moss and algae are two distinct organisms that can thrive on roofs under certain conditions. Moss is a non-vascular plant that requires a moist environment to survive. It tends to grow on north-facing roof planes that receive less direct sunlight and stay damp longer. Overhanging tree branches provide additional shade and drop debris on the roof, creating an ideal habitat for moss.

Algae, on the other hand, is a type of single-celled organism that appears as black discoloration and streaks on roofs. It tends to grow in coastal or humid climates where moisture is abundant. The most common type of algae, known as gloeocapsa magma or blue-green algae, protects itself from damaging ultraviolet rays by producing a dark pigmented sheath.

The Impact of Moss and Algae on Your Roof

While moss and algae may seem like harmless nuisances, they can have detrimental effects on your roof if left unchecked. Moss, in particular, has the potential to cause the leading edges of shingles to lift or curl, increasing the risk of shingle blow-off during wind events. In severe cases, moss build-up can also cause lateral water movement, resulting in moisture damage to the roof deck and potential leaks.

Algae, although not damaging to asphalt shingles, can significantly impact the aesthetics and long-term effectiveness of highly reflective or “cool” roofs. Additionally, the presence of algae on rooftops is unsightly and can spread from one rooftop to another through wind or animals, affecting an entire neighbourhood or complex.

Preventative Measures

Taking proactive steps to prevent moss and algae growth on your roof is essential. Here are some preventative measures you can implement:

  • Trim tree branches: Trim back overhanging tree branches to allow more sunlight to reach the roof and minimise debris accumulation, creating an environment less inviting for moss and algae growth.
  • Regular cleaning: Clear debris that begins to accumulate on the roof regularly. Use a leaf blower or a similar non-abrasive method as part of your regular maintenance program.
  • Ensure proper airflow: Direct air flows down the slope of the roof to avoid driving debris under the edges of the shingles.
  • Maintain clean gutters: Keep gutters clean to promote proper water drainage. Avoid allowing gutters from an upper roof to drain directly on a lower roof; extend the downspout from the upper roof into the lower gutter.
  • Consider preventative solutions: Explore options such as adding zinc or copper strips to the roof to prevent both algae and moss growth. Some asphalt shingles are also available with algae-resistant copper granules.

It’s important to note that adding zinc or copper strips to an existing roof is not recommended as it may cause damage or require breaking the sealant bond.

Cleaning Moss and Algae from Your Roof

When it comes to cleaning moss and algae from your roof, following proper techniques is crucial to avoid causing damage. Here’s a step-by-step process to effectively remove moss and algae:

  • Safety precautions: Before starting any roof cleaning, ensure your safety by using appropriate personal protective equipment, such as gloves and safety goggles.
  • Homemade cleaning solution: Create a homemade mixture by combining equal parts water and bleach. This solution is effective in washing away algae and moss without damaging your roof or shingles. However, be cautious with pressure level settings when applying the solution to prevent roof damage.
  • Soaking and scrubbing: If you’re removing moss, allow the cleaning solution to soak on the moss for 15 to 20 minutes. Afterward, gently scrub away the moss using a brush to ensure thorough removal.
  • Rinsing: After cleaning off moss or algae, rinse your roof thoroughly with low-pressure water to remove any residue. Avoid letting the solution dry completely, as this may prevent complete rinsing.
  • Additional treatments: In severe cases of moss growth, it may be necessary to apply multiple bleach treatments to kill all the moss. However, never use a pressure washer to clean an asphalt shingle roof, as it can cause granule loss and premature failure of the roof system.

Copper Strips as a Preventative Measure

As mentioned earlier, copper can be an effective deterrent for algae growth on your roof. Applying copper strips along the side of your roof, just below the roof vent or chimney, can help prevent algae from taking hold. When it rains, the water that washes down your roof will contain traces of copper, which are toxic to algae.

Hiring Professionals for Roof Maintenance

While DIY roof cleaning can be effective, it’s essential to consider hiring trained professionals for roof maintenance, including handling moss and algae growth. Trained roofers have the expertise and equipment to safely and effectively clean your roof while minimising the risk of damage. If you’re in the Sunshine Coast area, Sunshine Coast Roofers can connect you with reputable roofing companies that specialise in roof repairs and maintenance.


Proactively handling moss and algae growth as part of your roof repairs is crucial for the overall health and longevity of your roof. By implementing preventative measures and following proper cleaning techniques, you can effectively remove moss and algae from your roof while minimising the risk of damage. Remember, if you’re unsure or uncomfortable with cleaning your roof yourself, it’s always a good idea to consult with professionals who can provide expert advice and assistance. Maintain a healthy roof, and your home will thank you for it.For more information on roof repairs and maintenance, contact Sunshine Coast Roofers for a free estimate.