What Causes Black Stains on a Roof?

The short answer to the question, "Why are there black stains on roof shingles?" is one word: algae. As roof shingles get wet, they can create environmental conditions that support algal growth. Algae might seem harmless, but over time, the algae can degrade the structure of the shingle material. 

Several types of algae, including Gloeocapsa magma, grow on roofs. They can grow on many types of roofs, including asphalt, slate, clay, metal, concrete, and architectural shingles.

If you have asphalt shingles, like many homeowners, do not neglect algal growth on your roof. Asphalt shingles contain limestone, which algae use as a nutrient. As the algae consume limestone, the shingles become less durable,

Without treatment, algae on roofs can lead to missing shingles, leaks, and reduced structural integrity. Some experts view algae on roof shingles as an aesthetic problem rather than a source of damage, while others point out that algae can shorten the lifespan of a roof.

If your roof shows signs of algae and your property is in northern Virginia, trust Low Cost Roofing, the roof repair specialists in Falls Church, VA, to treat algae and other threats to your roof.

Why Does Algae Develop on Shingle Roofs?

The roof’s exposure to water and sunlight provides a supportive environment for algae. Many forms of algae do better in limited sunlight, so they tend to grow on the north-facing side of roofs in the northern hemisphere. The dark color is part of the algae’s defense against bright sunlight. 

Algae can travel from wind-blown debris such as leaves and tree branches. Once they land on a damp section of the roof, algae cells proliferate until they cover the shingle surface.

What Can I Do About Algae on My Roof Shingles?

Fortunately, algae growth is easy for experienced roofing contractors to fix. Depending on your budget and the extent of algae growth, you can opt for long-term or short-term solutions.

Fight Discoloration with Household Bleach

The Asphalt Roofing Manufacturers Association recommends using a solution of roughly equal parts bleach and water to kill algae and reduce the black stains on roof shingles. They advise against using high-pressure power washing on asphalt shingles because the force of the water can damage or dislodge the shingles.

Replace Damaged Roof Shingles

Replacing shingles, particularly asphalt shingles, eliminates discoloration and removes any damaged sections that could become a weak point in your roof. 

Installing Algae-Resistant Shingles

Copper oxide kills algae, so some manufacturers add a layer of copper oxide to their algae-resistant lines of shingles. The expense of replacing your roof shingles will be worth it if it saves you the cost of repeatedly removing coatings of algae from your shingles.

Book a Service Call for Algae Treatment and Roof Repair by Low Cost Roofing

Don't let black stains on roof shingles keep you from taking pride in your roof. For affordable roof repair and replacement in Falls Church, VA, count on Low Cost Roofing for quality materials at affordable prices. We handle commercial and residential roofing projects.