Why is my shingles algae growth

RoofingUpdated March 2026

The answer to 'why is my shingles algae growth' is that algae growth on asphalt shingles is a common issue, often caused by moisture, shade, and warm temperatures. Algae can cause discoloration and deterioration of the shingles over time.

Some common causes of algae growth include: poor roof ventilation, overhanging trees or structures that block sunlight, and high humidity in the local climate. Symptoms include dark green or black streaks or spots on the shingles. While algae growth is primarily an aesthetic issue, it can lead to premature shingle deterioration if left untreated.

Sources

National Roofing Contractors Association— authority

OSHA Roof Cleaning Safety Guidelines— reference

This Old House: Removing Roof Algae— guide

Step-by-Step Guide

1
Clean the roof
You can try cleaning the algae yourself using a soft-bristle brush and a mild detergent solution, but be careful on the roof. For extensive algae growth, it's best to call a professional roofing contractor.
2
Apply an algaecide treatment
An algaecide treatment can help kill and prevent future algae growth. This is something a roofing professional can apply, or you can use a DIY algaecide product if the growth is limited.

Frequently Asked Questions

How can I prevent algae growth on my roof?

To prevent algae growth, ensure proper roof ventilation, trim back any overhanging trees or structures, and consider using algae-resistant shingles when it's time to replace your roof.

Is algae growth on my roof a serious problem?

Algae growth is primarily an aesthetic issue, but if left untreated, it can lead to premature shingle deterioration over time. It's generally not an urgent structural concern, but it's best to address it proactively.

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