Making roof shingles look new involves cleaning, removing biological growth, and addressing cosmetic issues without damaging the shingle's protective granules. The most effective method is a thorough but gentle cleaning to remove black algae streaks, moss, and dirt. Start by removing debris like leaves and branches with a soft broom from ridge downward. For black algae streaks caused by Gloeocapsa magma, use a shingle-safe cleaner. Manufacturers like GAF and Owens Corning recommend a solution of oxygen bleach, sodium percarbonate, mixed with water and mild soap, applied with a low-pressure garden sprayer, allowed to dwell 15 to 20 minutes, and rinsed gently with a garden hose, never a pressure washer which strips granules and voids warranties. Commercial products like Spray and Forget, Wet and Forget, and Roof Shampoo are designed to clean without rinsing and work over weeks with rain. For moss, kill it first with zinc sulfate or potassium salts, then gently sweep dead moss off after it dries. Trim overhanging branches to increase sunlight and reduce shade that promotes growth. Replace any missing, cracked, or curled shingles with matching ones. Installing zinc or copper strips near the ridge helps keep the roof clean longer by preventing algae regrowth. There is no coating that truly makes old shingles new, and rejuvenator sprays offer limited benefit.
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