Those dark streaks or green patches on your roof might look like harmless discoloration—but they’re likely algae, moss, or mold, and they can silently damage your roof over time. Left untreated, these organic intruders compromise curb appeal, structural integrity, and energy efficiency.

Here’s how to identify, remove, and prevent algae, moss, and mold—and when to call a professional.

Causes of algae, mold, and moss on the roof

These growths thrive in moist, shaded environments, especially in humid or rainy climates. Common causes include:

• Overhanging trees, which provide shade and drop organic debris

• Clogged gutters, which trap moisture at roof edges

• Poor roof ventilation, which creates condensation

• North-facing slopes, which receive less sunlight and stay damp longer

• Older or porous roofing materials, which hold moisture

How algae, mold, and moss damage your roof?

Each of these organisms possess different risks to your roofing system:

1. Algae

Usually appears as black streaks, particularly on asphalt shingles. While not immediately destructive, algae holds moisture and gradually breaks down roofing materials.

2. Mold

Can grow underneath shingles or in damp attic areas. It’s a health hazard and can cause rot in your roof decking and insulation.

3. Moss

A thick, green plant that grows in clumps and lifts shingles as it expands, allowing water to seep underneath.

4. Mold & algae growth combined

The presence of both can accelerate shingle decay and increase the risk of leaks, especially in shaded or poorly ventilated roofs.

5. Flashing & sealant issues

Organic growth can compromise flashing and seals, especially around vents, chimneys, and valleys—leading to internal water damage.

How to prevent roof algae, moss, and mold?

Prevention is the key to avoiding expensive roof damage and prolonging your roof’s life. Here’s how:

1. Trim overhanging branches

This allows more sunlight to reach the roof, keeping it dry and reducing moss or algae growth.

2. Clean your gutters

Clogged gutters cause water buildup along the roofline. Regular cleaning prevents trapped moisture and organic debris accumulation.

3. Use algae-resistant shingles

Opt for shingles with copper or zinc granules, which inhibit algae growth. These are especially recommended in shaded areas.

4. Install zinc or copper strips

Installed near the roof ridge, these strips release metal ions when it rains, killing moss and algae naturally.

5. Keep your roof clean

Remove debris like leaves and branches regularly. Avoid pressure washing, which can damage shingles—instead, use soft wash treatments or professional services.

6. Improve ventilation

A well-ventilated attic reduces heat and moisture buildup, making your roof less hospitable to mold and algae.

Roof inspection and cleaning with Masterpiece Roofing

At Masterpiece Roofing, we provide expert roof inspections and safe cleaning services tailored to the needs of New England homes. Whether your roof is starting to show signs of organic growth or already needs intervention, we help restore its integrity, safety, and appearance.

Our team uses low-pressure cleaning methods, algae-resistant treatments, and detailed inspections to stop the problem at the root.

Contact Masterpiece Roofing today for roof cleaning, treatment, or a full inspection—and keep your home protected from the top down.