Properly maintained, a quality metal roof can last for a lifetime. To ensure that your roof stays in top condition, a regular cleaning is suggested. This is particularly important if your roof is in an area that lends itself to the buildup of mold or mildew.
How to Clean Metal Roofs
Assess the condition of your roof. An old roof, with excess paint and corrosion will require extra steps in preparation, cleaning, and restoration. A relatively new, or well-cared for roof will require less work.
Ensure that you can safely work on the roof, and reach all the areas you wish to clean with ease.
Scrape away any excess paint or corrosion if necessary. A wire brush will be necessary for this step. Do not use metal implements on the roof unless absolutely necessary.
Prepare a solution of TriSodium Phosphate (TSP) (available at most paint stores) and water, mixing 1/2 cup per gallon of water. Using a soft brush, apply the TSP to any mold or mildew covered areas, scrubbing until clean. Rinse the areas you've worked on with water.
Spray the entire roof with a power washer. Plain water is fine for most applications. If necessary, repeat the process.
If you had to remove corrosion or damaged paint in step 3, prime and paint those areas now.