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At Rainguard Roofing, based in Twin Falls and serving all of Southern Idaho, we’re familiar with the unique challenges our clients face when it comes to roof maintenance. One common issue that can affect the aesthetic appeal of your home is algae growth on asphalt shingles, which may result in unsightly brown or black streaks across your rooftop.

It’s easy to confuse these dark streaks for soot, dirt, or tree droppings, which typically cause only localized discoloration. However, the discoloration caused by algae is a widespread issue, especially prevalent in areas exposed to warm, humid conditions—a situation not uncommon in various parts of the U.S., including here in Idaho.

The culprit behind these dark streaks is a species of cyanobacteria known as Gloeocapsa magma, an airborne algae that finds a welcoming home on our roofs. This is different from the green algae or moss you might find in areas of your roof that receive less sunlight or have higher moisture levels.

Can You Tackle Algae Discoloration Yourself?

While algae discoloration can be stubborn, it’s possible to lighten these dark streaks by applying a diluted solution of chlorine bleach and water. However, we at Rainguard Roofing stress the importance of consulting with a professional roofing expert before attempting any cleaning. Roof safety is paramount, and the cleaning process can make your roof slippery.

Steps to Lighten Algae Discoloration:

  1. Protect Your Ground Vegetation: Before applying any solution, ensure the plants directly beneath the affected area are covered to protect them from chemical runoff.
  2. Prepare the Solution: Mix equal parts bleach and water (a 1:1 ratio) and gently spray this solution over the algae-affected areas.
  3. Wait and Rinse: Let the solution sit for 10-20 minutes, then rinse off with water, ensuring you thoroughly flush both the roof and the surrounding greenery.

It’s important to note that using high-pressure washing equipment or scrubbing can damage your shingles by removing granules, thus shortening the lifespan of your roof.

The Impact of Algae on Asphalt Shingles

While algae growth is mainly an aesthetic concern and does not directly impact the performance of asphalt shingles, it can significantly affect your home’s curb appeal. At Rainguard Roofing, we understand that the appearance of your home is important.

Algae-Resistant Shingles: The Long-Term Solution

To combat algae growth effectively, Rainguard Roofing recommends considering asphalt shingles with algae-resistant (AR) features. These shingles are designed with copper-lined mineral granules to inhibit algae growth, offering a durable solution to keep your roof looking pristine.

Observations have shown that metals like copper naturally reduce algae growth, a discovery made apparent by the lack of algae staining beneath metal vents or flashing on roofs.

Warranty and Protection

Rainguard Roofing offers products featuring StreakGuard® Protection, incorporating this algae-inhibiting technology to ensure your roof stays beautiful and virtually maintenance-free. This protection is a testament to our commitment to quality and customer satisfaction, providing a robust solution against the common issue of algae growth on roofs.

For homeowners in Southern Idaho, Rainguard Roofing is your go-to source for expert advice and solutions tailored to the specific needs of your home. Our range of algae-resistant shingle options ensures that you can find the perfect fit for your home’s style and protection needs.


The technical information provided herein is offered as a courtesy to our customers and is based on our extensive experience and knowledge in roofing. However, it is essential to consult with a professional roofing contractor, like Rainguard Roofing, to address your specific needs and for any actions taken based on this information. Rainguard Roofing disclaims liability for any damage or injury resulting from the use of the information in this document.

At Rainguard Roofing, we’re dedicated to keeping your home protected and looking its best. If you’re battling algae growth or any other roofing concern, reach out to us—your local roofing experts in Southern Idaho.

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