Roof Cleaning and Moss Removal in Louisville

Dealing With Moss, Algae, and Black Streaks

Louisville's humid climate creates ideal conditions for biological growth on roofs. Here's what's growing up there and how to deal with it safely.

What's Growing on Your Roof?

Black Streaks (Gloeocapsa Magma)

Those dark streaks running down your roof aren't dirt — they're algae. Gloeocapsa magma feeds on the limestone filler in asphalt shingles. It's the most common roof discoloration in Louisville.

Is it harmful? Mostly cosmetic. Heavy growth can accelerate granule loss slightly, but the primary issue is appearance and potential impact on home value.

Moss

Green, fuzzy growth that thrives on north-facing and shaded roof areas. Unlike algae, moss is physically destructive — its root system lifts shingle edges, allowing water intrusion.

Is it harmful? Yes. Moss causes real damage and should be removed.

Lichen

A combination of algae and fungus that appears as circular patches of white, green, or gray. It's strongly adhesive and very difficult to remove without damaging shingles.

Is it harmful? Moderately. It's harder on shingles than algae but less immediately destructive than moss.

The #1 Rule: NEVER Power Wash Your Roof

Power washing strips protective granules from shingles, shortening their lifespan by years. It also forces water under shingle edges, potentially causing leaks. Every major shingle manufacturer explicitly prohibits power washing and will void your warranty if it's done.

We cannot stress this enough: do not let anyone power wash your roof.

Safe Cleaning Methods

For Algae (Black Streaks)

Mix a 50/50 solution of household bleach and water. Apply with a garden sprayer (not a pressure washer). Let it sit for 15–20 minutes, then rinse gently with a garden hose. Work in sections, starting from the top.

Safety: Protect landscaping by wetting plants before and after treatment. Work on a cloudy day to prevent the solution from evaporating too quickly.

For Moss

Apply a moss-killing product (zinc sulfate or copper sulfate-based) according to directions. Allow several weeks for the moss to die and dry out. Dead moss can be gently brushed away with a soft broom.

Do NOT scrape live moss aggressively — it can tear shingle surfaces.

Prevention

• Install zinc or copper strips along the ridge — rainwater washes metal particles down the roof, inhibiting growth
• Trim trees to increase sunlight and airflow
• Choose algae-resistant shingles (with copper-infused granules) when you replace your roof

When to Call a Professional

• Moss growth is extensive (covering more than 20% of the roof)
• You're uncomfortable on a ladder or working at height
• Lichen has bonded to shingles (requires careful treatment to avoid damage)
• You're unsure whether the growth is cosmetic or causing structural damage

Questions about roof cleaning? Call (502) 208-5432.

Related Reading

• Signs You Need a New Roof →
• How to Extend Your Roof's Lifespan →

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