Mold or algae streaks—typically appearing as black lines—are a common issue on the shaded sides of asphalt shingle roofs, especially in humid or tree-covered areas. The good news is they can be safely removed with the right approach.

Here’s a step-by-step method recommended by CertainTeed:

Use a gentle cleaning solution:
Mix a solution of 50% water and 50% household bleach. Add a small amount of liquid dish soap to help the solution stick to the roof surface. Avoid using harsh or high-strength chemicals that can damage shingles.
Apply the solution carefully:
Using a pump sprayer, gently apply the solution to the affected areas. Start at the bottom of the roof and work upward to prevent streaking. Let the solution sit for about 15–20 minutes, but don’t let it dry completely.
Rinse thoroughly with low pressure:
Rinse the roof using a garden hose with low water pressure. Do not use a pressure washer, as it can damage the shingle granules and shorten the life of your roof.
Prevent future streaks:
Consider installing copper or zinc strips near the roof ridge. Rainwater running over these metals will inhibit algae growth. Also, trimming overhanging branches can reduce shade and moisture buildup.
At CertainTeed, we also offer algae-resistant asphalt shingles with copper-infused granules designed to combat this problem before it starts. If you’re renovating or replacing your roof, choosing algae-resistant shingles is a smart, long-term investment.

If the mold streaks are severe or you’re unsure about working on your roof safely, it's always best to contact a professional roofing contractor.

— CertainTeed Roofing Expert

for more details please visit - Roofing Shingles

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phone no - 080 4697 8623

Saint-Gobain Grindwell Norton Limited Devanahalli Road