Dirty Roof

Black streaks on your roof are often the result of a hardy, blue-green algae known as Gloeocapsa magma. This organism spreads through airborne spores, flourishes in warm, humid climates, and feeds on the limestone filler found in modern asphalt shingles, leading to dark, unsightly streaks that are especially prevalent on shaded or north-facing roofs.

Why It Happens:

The algae thrives in moist, shaded areas, consuming the mineral fillers in shingles. It is more frequently found on older roofs or in humid environments, often spreading from neighboring roofs, which can ultimately prevent roof damage.

Is It Harmful?

While primarily a cosmetic issue that diminishes curb appeal, the presence of algae can lead to premature aging of shingles, retain moisture that fosters moss and mildew growth, and reduce the roof's energy efficiency by absorbing heat.

How to Remove It:

Avoid using a pressure washer, as it can damage or destroy shingles. Instead, opt for a soft wash roof cleaning approach, applying a specialized cleaning solution (often a mixture of water, bleach, or sodium hypochlorite) to effectively kill the algae, followed by a gentle rinse.

How to Prevent It:

To help prevent roof damage, install copper or zinc strips along the ridge of your roof. As rainwater washes the metal ions down, they become toxic to algae and inhibit future growth. Additionally, when replacing your roof, consider choosing algae-resistant shingles that often contain copper-infused granules.