Why Are Roofs in Norfolk County Covered in Algae? Understanding the Black Streaks and Green Algae and How to Remove Them Safely

If you've noticed black streaks or dark patches spreading across roofs throughout Norfolk County, you're not alone. From Simcoe and Port Dover to Delhi, Waterford, and the surrounding rural communities, roof algae is one of the most common issues homeowners face.

Many people assume these stains are simply dirt or mold, but the truth is they're caused by a living organism that thrives in our local climate. Left untreated, roof algae can affect both the appearance and longevity of your roof.

What Is Roof Algae?

The black streaks you see on asphalt shingles are most commonly caused by a type of algae called Gloeocapsa magma. This airborne algae spreads through spores carried by wind, birds, and other natural sources. Once it lands on a roof, it begins to grow in areas where moisture lingers.

As the algae matures, it forms the dark stains that often start on the north-facing side of a roof or in shaded areas before gradually spreading across the entire surface.

Why Is Roof Algae So Common in Norfolk County?

Norfolk County's climate creates ideal conditions for algae growth.

Several factors contribute to the problem:

• High humidity throughout the spring, summer, and early fall.

• Morning dew that keeps shingles damp for hours.

• Tree cover that limits sunlight and slows drying.

• Warm temperatures that encourage biological growth.

• Proximity to Lake Erie, which can increase moisture in the air.

  
  

Even newer roofs can develop algae within just a few years if conditions are right.

Is Roof Algae Harmful?

While algae doesn't usually cause immediate leaks, it should not be ignored.

As algae spreads, it retains moisture against the roof surface. Over time, this constant moisture can contribute to:

• Premature aging of asphalt shingles.

• Reduced curb appeal.

• Higher roof surface temperatures due to darker staining.

• Conditions that encourage moss and lichen growth, which can cause more serious damage.

  
  

Cleaning the roof before algae becomes severe helps preserve the appearance and lifespan of your roofing materials.

Why Pressure Washing Is the Wrong Choice

One of the biggest mistakes homeowners can make is using a pressure washer on an asphalt shingle roof.

High-pressure water can:

• Remove the protective granules from shingles.

• Damage sealant strips.

• Force water underneath roofing materials.

• Shorten the life expectancy of the roof.

  
  

Although the roof may look clean immediately afterward, the damage caused by pressure washing can be permanent.

The Importance of Soft Washing

Professional roof cleaning should always be performed using a soft washing system.

Soft washing uses low-pressure equipment combined with specially formulated cleaning solutions that eliminate algae at its source instead of simply blasting away the visible stains.

The process:

• Kills the algae rather than just removing the surface discolouration.

• Cleans without damaging shingles.

• Helps delay future regrowth.

• Restores the roof's original appearance safely.

  
  

Instead of relying on force, soft washing relies on chemistry to do the work.

Why Using the Right Chemicals Matters

Not all roof cleaning products are created equal.

Using the wrong chemicals—or mixing them incorrectly—can damage roofing materials, stain siding, harm landscaping, or fail to eliminate the algae completely.

Professional roof cleaning solutions are carefully selected and diluted to:

• Effectively kill algae and organic growth.

• Be compatible with asphalt shingles.

• Minimize impact on surrounding plants and landscaping when proper procedures are followed.

• Provide a longer-lasting clean than water alone.

  
  

At Under Pressure Power Washing we take precautions by protecting vegetation, rinsing surrounding areas, and applying the cleaning solution evenly for the best results.

Don't Wait Until the Roof Looks Bad

Roof algae doesn't disappear on its own. In fact, it typically becomes more widespread each year as spores continue to grow and spread.

Addressing the problem early can:

• Restore your home's curb appeal.

• Help extend the life of your roof.

• Prevent moss and lichen from becoming established.

• Protect one of your home's most valuable investments.

  
  

Keep Your Roof Looking Its Best

Living in Norfolk County means enjoying beautiful scenery, nearby lakes, and lush landscapes—but it also means dealing with humidity that encourages algae growth. The good news is that roof algae can be removed safely and effectively when the proper soft washing methods and professional cleaning solutions are used.

If your roof has developed black streaks or discolouration, avoid the temptation to pressure wash it. Choosing a professional soft wash treatment is the safest way to restore your roof while protecting it for years to come.