Black streaks and moss on your roof

What you’re seeing

Black streaks on a shingle roof are usually a type of algae. It spreads with wind and grows best on shady, damp parts of the roof. Green moss and crusty lichen grow in the same conditions, often on north-facing sections and under trees.

Why it matters

• Moss holds water against shingles and can lift their edges.
• Water held on the roof can lead to leaks and shorter roof life.
• Streaks make the whole home look older than it is.

What not to do

Don’t pressure wash a roof. High pressure strips the granules that protect shingles from the sun, and it can force water under them.

The fix

A soft-wash treatment kills algae, moss and lichen at low pressure. Loose moss is brushed off by hand, gutters are rinsed, and any remaining streaks fade over the next few rains. That’s how our roof cleaning works.

Keep it from coming back

• Trim branches that shade the roof.
• Keep gutters clear so water drains. Gutter cleaning twice a year helps.
• Plan a roof treatment every few years.