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The black streaks running down asphalt shingles are a blue-green algae, not dirt, and the method you choose to remove them decides whether the roof gains years or loses them. Sodium hypochlorite blends kill algae, moss and lichen on contact and are what soft-wash contractors use; sodium hydroxide blends are gentler on planting but slower; zinc and copper strips at the ridge prevent regrowth rather than clean. Pressure washing strips the granules that protect the asphalt and voids most shingle warranties. This guide covers the three cleaner families, a safe low-pressure application sequence, dwell and rinse timing, plant protection, ladder safety and how long results realistically last.
Roof cleaning products are chemistry, not pressure. What removes algae and moss from a shingle roof is a solution left to dwell and then rinsed gently — anything that relies on force removes the granules with the growth.
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Soft washing — a low-pressure application of a cleaning solution, left to dwell, then rinsed gently. The chemistry does the work, which is why it removes algae without removing granules.
Sodium hypochlorite based products are the fastest-acting option and are widely used, but they need the planting below wetted down before and rinsed after. Sodium percarbonate is gentler and slower.
Not if it is soft washed. It will if it is pressure washed or scrubbed — both remove the granules that are the shingle's UV protection and fire rating, and most manufacturers void the warranty over it.
Zinc or copper strips near the ridge, so rain carries a trace of metal down the roof, plus cutting back overhanging branches. Both are cheap next to repeating the clean.