The Truth About Roof Mold and Algae—And How to Get Rid of It

Maintaining your roof isn’t just about shingles and gutters. In East Tennessee’s warm, humid climate, mold and algae are some of the most overlooked threats to your roof’s longevity—and your home’s appearance.

Left unchecked, these growths can lead to roof damage, reduced energy efficiency, and even health concerns. The good news? With regular maintenance and the right approach, you can eliminate roof mold and algae and keep your home protected.

What Causes Mold and Algae to Grow on Your Roof?

If you’ve ever noticed dark streaks or green patches on your roof, you’re likely dealing with mold, algae, or a combination of both. These organisms thrive in moist, shaded environments, especially on north-facing roofs that receive less sunlight.

Common causes include:

• High humidity and frequent rainfall (common in the Knoxville area)

• Poor attic ventilation, which allows heat and moisture to rise and linger

• Overhanging trees, which provide shade and drop organic material

• Clogged gutters, allowing water to pool and seep beneath shingles

Why Mold and Algae Are a Problem

While some homeowners think those dark streaks are just cosmetic, they can cause real damage over time. Here’s why mold and algae need to be addressed:

• Reduced roof lifespan: Algae feeds on the limestone filler in asphalt shingles, gradually degrading them.

• Increased moisture retention: Mold and algae hold water against your roof, leading to rot, leaks, and damaged decking.

• Energy loss: A dark, algae-covered roof absorbs more heat, making your cooling system work harder.

• Health concerns: In severe cases, mold can make its way into attic spaces and affect indoor air quality.

How to Safely Remove Mold and Algae from Your Roof

It’s important to take the right steps—the wrong methods can damage your shingles or void your warranty. Here’s how professionals like Garrett Roofing tackle roof mold and algae safely:

1. Soft Wash Cleaning

Unlike power washing, soft washing uses a low-pressure sprayer with a specialized cleaning solution that kills algae and mold at the source without damaging your shingles.

2. Algae-Resistant Shingles

If your roof is due for replacement, ask about algae-resistant shingles. These contain copper or zinc granules that naturally inhibit algae growth—great for homes in humid areas like Knoxville.

3. Trim Overhanging Trees

Less shade means less moisture. Keeping your roof exposed to sunlight helps prevent mold and algae from forming in the first place.

4. Improve Ventilation and Drainage

Proper attic ventilation helps reduce internal moisture, while clear gutters keep water from pooling along your roofline.

Preventative Maintenance Tips

The best way to avoid dealing with mold and algae is to make roof maintenance part of your home care routine:

• Schedule a roof inspection every year (especially after wet seasons)

• Keep your gutters clear and your attic well-ventilated

• Watch for early signs of discoloration or soft spots

• Don’t wait until it spreads—treat small patches early

Protect Your Home from the Top Down

Roof mold and algae aren’t just an eyesore—they’re a signal your roof needs attention. Taking care of your roof now helps avoid expensive repairs later and keeps your home looking its best.

Looking for roof repair or installation near you?

With 20+ years of experience, Garrett Roofing’s dedicated team of experienced professionals is ready to partner with you to give you the quality roof you deserve. Contact us to get a quote today!