Roof cleaning questions answered by D.C. area experts

Roof cleaning questions answered by D.C. area experts

My roof is in the shade much of the day, and it has areas of discoloration that I suspect may be mildew or something similar. Is roof cleaning necessary? Is it safe for the roof? - Angie's List member Dora Garrett

The discoloration comes from algae, says Paulo Baesse, owner of highly rated Roof Real Clean in Falls Church, Va. "Curb appeal is important, but the biggest thing is the damage it does to a roof," he says. "You have a living organism eating your shingles."

Joan Crowe, technical services director for the National Roofing Contractors Association, which takes no position on whether roof cleaning is necessary, says discoloration is usually a problem that affects asphalt shingles. "You can clean it, but the discoloration will come back," she says.

Most homeowners choose to clean their roofs for aesthetic reasons, Crowe says. She recommends using a mild bleach-water solution with a soft brush or sponge but advises against using pressure washers, which can damage shingles.

Victor Fedoseyev, owner of highly rated Roof Clean Bright in Rockville, Md., says shingle manufacturers offer products treated with copper or zinc to inhibit algae growth, but their effect wears down over time. His company uses a mild cleaner with a low-pressure wash to clean discolored roofs.

Baesse says his non-chlorine cleaner and low-pressure wash typically prevents algae growth for several years. He estimates the average cleaning costs $350 to $795, depending on the roof's size, pitch and height.

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He uses low pressure. He is damaging roofs. NO pressure at all should be used!

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