- 1). Fill a power washer with cold water. Set the power washer to a pressure of 1,000 to 1,500 PSI and use a 15-degree spray fan. Do not use too much pressure as this can damage the shingles. Hold the power washer's sprayer 8 to 12 inches from the shingles and spray. Move from the top of the roof down, being careful to stand only on the dry part of the roof. If you cannot power-wash or would prefer not to, move on to the next steps.
- 2). Fill a garden pump sprayer with one part chlorine bleach, 1/4 cup trisodium phosphate and three parts water. Spray the solution onto the shingles, working from the top of the roof down. Be careful not to spray shrubbery or other parts of the building. Use a rate of 1 to 1 1/2 gallons per hundred square feet. Let the solution set for 15 to 30 minutes. For tough stains, move on to the next step before rinsing.
- 3). Scrub stains with a sponge or other gentle cloth. To avoid damaging asphalt shingles, a gentle method is best. If you have wood or other shingles, a more abrasive sponge may speed the process.
- 4). Rinse the solution off of the shingles with a hose. For asphalt shingles, use a gentle setting. For wood or other shingles, rinsing with a power washer can give better results.
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