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Those dark stains aren't dirt — they're alive and eating your roof.

High-pressure water can do serious damage in seconds. Pressure washing damages shingles, shortens roof lifespan, and may void warranties. Water forced under shingles can cause mold, leaks, and rot.

QDEAR TIM: My roof needs cleaning. It's a newer asphalt shingle roof, but parts of it are covered with moss, lichens and algae. Is a pressure washer a good tool for cleaning roof shingles? Will it ...

Your roof takes a beating from weather, sun, and debris from nearby trees. After years of abuse it can start to look dirty, with algae growth, mold and dark streaks. You might be tempted to pressure ...