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It may require stronger cleansers or chemicals, higher-pressure spray, or scrubbing to completely remove algae from a metal roof. Start with a mild cleanser; if that doesn’t work and you're comfortable doing so, use a stronger mix of ⅓ cup of laundry detergent, 1 quart of bleach, and 3 quarts of water to gently scrub the algae with a soft-bristled brush. If algae is present across large portions of your roof, doesn’t come off with gentle scrubbing and cleansers, or is in hard-to-reach areas, this may be a job better left to a pro.

The average cost to clean a roof is around $500, but prices can fall between $150 to $1,000 or more. The size and complexity of your roof are the most significant cost factors, as larger roofs and those with various bump-outs and gables will increase your cost. Your roof material will also make a difference. An asphalt roof will require more labor, as your professional will need to be careful not to damage the shingles. A metal roof can stand up to more intense scrubbing and shouldn’t take as long to clean.

It generally involves soft washing with eco-friendly detergents to remove contaminants, avoiding high-pressure methods that can damage materials.

Soft washing chemicals typically consist of a mix of sodium hypochlorite (or a chemical component of bleach) and water. While sodium hypochlorite and bleach are often thought to be the same thing, there is one small but key difference between the two: sodium hypochlorite comes in powdered rather than liquid form, which means that it’s also more concentrated and more effective from less product overall.