What roof moss prevention products actually work?
Short answer. The prevention products with the best track record are zinc or copper strips installed just below the ridge, which release metal ions with every rain, zinc-based granule or spray treatments applied periodically, and algae-resistant shingles made with copper-containing granules when the roof is replaced. None of them overcome deep shade and constant dampness, so trimming trees is part of any prevention plan.
Product categories
- Zinc strips: a few inches wide, fastened under the ridge cap or the course below so only a narrow band is exposed. Rain carries zinc down the slope, and the effect weakens farther from the strip, so long slopes may need a second row.
- Copper strips: more potent than zinc but costlier, and can leave green staining on light surfaces over time.
- Zinc sulfate granules or sprays: applied to affected areas once or twice a year. Runoff can harm plants.
- Algae-resistant shingles: major manufacturers offer shingles with copper-containing granules aimed at algae streaking; they may slow moss too. Algae resistance is usually covered by a separate, limited warranty.
What does not work well
- Galvanized flashing near the ridge: the zinc coating is thin and short lived.
- Pressure washing: removes moss but also granules, shortening shingle life.
- Painting or coating asphalt shingles: can trap moisture and may affect warranties.
Installation cautions
Strip fasteners should be covered by the overlying shingle or sealed, because exposed nails through shingles become leak points. Strips should never dam water or debris. See moss and lichen on roofs and trees and your roof.