How Does Summer Sunlight Impact Algae Growth on Roofs?

by | Jun 9, 2025 | roof cleaning

A Good Front Window Cleaning and Pressure Washing

Warm temperatures, humid air, and long hours of sunshine are hallmarks of summer in Highlands Ranch, CO. But while summer feels great for backyard BBQs, it’s also a prime season for an unwelcome guest—roof algae. Those dark black streaks or green patches creeping across your shingles? That’s not just dirt. It’s likely a combination of algae, moss, and even mold, all of which thrive in the summer heat and humidity.

If left unchecked, this growth doesn’t just hurt your curb appeal—it can cause long-term damage to your roof. Here’s what every homeowner needs to know.

1. Understanding Roof Algae and Black Streaks

Those mysterious dark stains on your roof are often caused by a type of blue-green algae known as Gloeocapsa magma.

Why you’re seeing more in summer:

  • Algae feeds on the limestone filler in asphalt shingles.
  • It flourishes in hot, humid weather—common during Highlands Ranch summers.
  • Once it appears, it spreads quickly down the roof, forming black streaks.

These black stains aren’t just ugly—they’re acidic and can wear away your shingles over time. Regular roof cleaning services can remove these stains and prevent permanent damage.

“What are the black streaks on my roof?”
They’re not just dirt—they’re a form of algae that feeds on your shingles and thrives in the summer sun.

2. Why Moss and Lichen Love Summer Too

Algae isn’t the only problem. Moss and lichen often grow in tandem with algae, especially on shaded or north-facing roof slopes.

How moss grows:

  • It starts as a thin green film in spring.
  • Summer warmth and humidity speed up its growth.
  • Moss holds moisture, which leads to shingle rot and wood damage.

Moss grows roots into your shingles, lifting them and making your roof more vulnerable to wind and water. If your roof feels spongy or looks uneven, moss may be the culprit.

Soft washing—not pressure washing—is the safest way to remove moss without damaging your shingles. A Good Front uses specialized equipment to gently clean your roof.

3. How Summer Sunlight Fuels Algae Growth

You’d think the sun would dry things out and kill algae, right? Not quite.

Here’s why summer sunlight actually worsens algae growth:

  • The UV exposure weakens shingles, making it easier for algae to take hold.
  • Morning dew and high humidity in Colorado’s summer climate create a daily moisture cycle that algae love.
  • The sun heats the roof, speeding up microbial activity and helping algae grow faster.

The darkest roof areas are often the hottest—and most algae-prone. Shaded sections stay wet longer, while sun-exposed areas experience the most heat stress.

4. The Cost of Ignoring Roof Algae and Moss

Letting organic growth fester through the summer can shorten your roof’s lifespan and cost you thousands in repairs.

Risks of not cleaning your roof:

  1. Shortened shingle life due to acidic algae and moss roots.
  2. Increased utility bills—algae-darkened roofs absorb more heat.
  3. Water damage from lifted or cracked shingles.
  4. Mold and mildew entering your attic or HVAC system.
  5. A dramatic drop in curb appeal, especially if you plan to sell.

5. How to Prevent Roof Algae Growth This Summer

While it’s nearly impossible to prevent algae spores from landing on your roof, you can prevent them from thriving.

Prevention tips:

  • Trim overhanging trees to increase sun exposure and air circulation.
  • Clean gutters regularly to avoid moisture pooling.
  • Schedule annual roof cleaning to remove early growth before it spreads.
  • Use algae-resistant shingles if you’re replacing your roof.
  • Ask about professional soft washing to sanitize and protect your roof surface.

“Can you clean algae off a roof yourself?”
Technically, yes—but it’s dangerous, time-consuming, and if done incorrectly, can cause more damage. It’s safer and more effective to hire pros like A Good Front who specialize in soft wash roof cleaning.

Don’t let the summer sun turn your roof into a breeding ground for algae and moss. With the right roof cleaning strategy, you can protect your investment, reduce cooling costs, and boost your home’s appearance—all without lifting a ladder.

Call A Good Front today at 720-545-8422
Visit agoodfront.com
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Beat the summer grime before it beats up your roof. Your Highlands Ranch home deserves the best—give it the clean it needs.