Have you looked up lately and noticed black streaks creeping across your roof? You’re not alone. Those unsightly stains are a common sight for homeowners here in Summerville, SC—especially in our warm, humid climate. But what are they exactly? And more importantly, are they dangerous?

Let’s break it down. In this blog, we’ll cover:

What causes black streaks on your roof
Why you shouldn’t ignore them
How to safely remove them with soft washing
When to call a professional roof cleaner like Soft Wash Pros

What Are the Black Streaks on My Roof?

Those dark streaks on your roof aren’t just dirt—they’re usually algae.

Specifically, the culprit is Gloeocapsa magma, a hardy blue-green algae that thrives in humid environments like ours in the Lowcountry. Over time, this algae:

Clings to asphalt shingles
Feeds on the limestone filler inside them
Spreads down the roof in dark, streaky trails

It may look like dirt or soot—but it’s actually living bacteria eating away at your roof material.

Why Should I Worry About a Black-Stained Roof?

A few dark lines may not seem like a big deal, but they can lead to serious roof issues if ignored:

Shingle Damage
The algae slowly eats away at the protective granules on your shingles, shortening your roof’s lifespan.
Heat Retention
Black streaks trap more heat, raising your cooling bills in spring and summer.
Mold and Mildew Growth
Moisture-loving bacteria and fungi thrive on shaded, algae-covered roofs—and that can spread to your siding and attic.
Curb Appeal Crash
Stained roofs make your home look old, dirty, and neglected—even if everything else is pristine.

A clean roof can actually increase your home’s value and extend the life of your shingles.

Can I Pressure Wash My Roof to Remove the Black Streaks?

No! While pressure washing might seem like a quick fix, it can actually cause serious damage.

Here’s why:

High pressure can dislodge shingles
It strips off the granules that protect them
Water can force its way under shingles, leading to leaks

Instead, professionals use a method called soft washing—a low-pressure, high-solution approach that safely dissolves algae, moss, and mold without damaging your roof.

What’s the Best Way to Clean a Black-Streaked Roof?

At Soft Wash Pros, we use a soft wash system specifically designed for roofs. It includes:

Eco-friendly cleaning agents that target organic growth
Low-pressure application that won’t damage shingles or flashing
Thorough rinsing to leave your roof looking like new
Optional preventative treatment to help slow algae regrowth

You’ll be amazed at the before-and-after difference—and your roof will thank you.

How to Prevent Black Streaks from Coming Back

While there’s no way to stop algae entirely, there are a few smart steps you can take:

Trim tree branches to let more sunlight hit your roof
Keep gutters clean to prevent moisture buildup
Install zinc or copper strips near the roof ridge (algae hates metal)
Schedule routine roof cleaning every 1–2 years

Need help staying on schedule? Soft Wash Pros offers annual and seasonal service plans.

FAQs About Roof Algae and Black Streaks

Q: Is roof algae dangerous to my health?
A: Not directly—but it creates the perfect environment for mold and mildew, which can pose health risks if they spread indoors.

Q: Will my homeowner’s insurance cover roof damage from algae?
A: Most policies don’t cover preventable damage, so regular cleaning is essential for protecting your roof investment.

Q: Can I clean it myself?
A: It’s not recommended. Roof cleaning requires the right chemical mixture, safety precautions, and technique. One misstep could damage your roof—or lead to injury.

Don’t Let Algae Win—Call Soft Wash Pros Today!

If your roof is looking streaky, dark, or discolored, don’t wait. The longer algae sits, the more damage it can do.

Soft Wash Pros provides:

Safe, effective roof soft washing
Full exterior cleaning services
Local, friendly technicians you can trust

Call us at (843) 696-6121
Visit washmyhouse.org
Check us out on Google Maps

Restore your roof’s beauty and protect your home—one gentle wash at a time.

What Turns My Roof Black?

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