Roof Care · 2026-02-19

What Causes Black Streaks on Roofs in Fort Wayne (and How to Get Rid of Them)

Those dark streaks on Fort Wayne roofs aren't dirt. They're a living organism, and they're shortening the life of your roof every day they're up there.

The Streaks Are Algae

The black streaks running down asphalt shingle roofs are a specific algae called Gloeocapsa magma. It feeds on the limestone filler in asphalt shingles, which is why it's been growing more aggressively over the past few decades — modern shingles have higher limestone content for fire-resistance ratings.

Why They Run Downward

Gravity. The algae starts at the top of the roof (often near tree-shaded areas), and rain spreads spores downhill. That's why streaks always run vertically and are usually worse on the north-facing slope.

Why It Matters (The Expensive Part)

Algae physically degrades shingles. Studies show that algae-infested roofs lose up to 40% of their expected lifespan. A roof rated for 25 years can fail at 15. At Fort Wayne re-roofing costs of $12,000–$25,000+, that's a serious financial hit.

The algae also reduces your roof's solar reflectance, which can increase summer cooling costs by 10–15%.

What Doesn't Work

  • Pressure washing: Destroys shingles. Voids your warranty. Don't do it.
  • Walking the roof and scrubbing: Damages granules. The protective layer.
  • Bleach poured from the ridge: Damages plants below and only treats the visible streaks, not the spores.
  • Zinc strips at the ridge: Helps prevent new growth but does nothing for existing algae.

What Does Work: Soft Washing

Professional soft washing is the only manufacturer-approved method. We apply a low-pressure sodium hypochlorite solution that:

  • Kills the algae at the cellular level
  • Penetrates spores so regrowth is delayed 2–5 years
  • Doesn't require walking on the roof or stripping granules
  • Costs $400–$900 versus $12,000+ for a new roof

The Visible Result

Most homeowners expect immediate clean shingles. Reality: the algae dies during the wash, but it takes 1–7 days of weather for it to fully break down and rinse away. The first day after, you'll see slight improvement. By day 7, the difference is dramatic.

How Often?

Most Fort Wayne roofs benefit from a soft wash every 3–5 years. Heavily shaded properties may need it every 2–3 years. If you see streaks, it's time.

Learn more about roof soft washing or get a free quote.

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