Do zinc strips stop roof moss?
Short answer. Zinc strips are thin bands of zinc installed just below the ridge so rain carries small amounts of zinc down the roof, which discourages moss and algae from regrowing. They work best as prevention on a cleaned roof, the effect weakens farther down long slopes, and they do not remove established moss on their own.
How they work
Each rain dissolves a tiny amount of metal from the strip and carries it down the shingles. Zinc and copper ions are toxic to moss, algae, and lichen, so growth struggles to take hold in the washed zone. Copper is generally more potent and longer lasting; zinc is less expensive.
Where they work and where they do not
- Best: moderate to steep slopes that get regular rain runoff from the strip, on a roof that has already been cleaned.
- Weaker: far down long slopes, where the concentration drops off. A second strip partway down may help on long runs.
- Weakest: heavily shaded slopes under dense trees, where conditions favor moss strongly, and low-slope sections where water spreads slowly.
- Not at all: on thick existing moss, which needs treatment and removal first.
Installing them
- Strips usually go just below the ridge cap on each slope, often tucked under the course above with only a narrow band of metal exposed to rain.
- Fasteners should be corrosion resistant and placed where the next course covers them, or sealed.
- Keep runoff in mind near ponds and vegetable beds.
Built-in protection
Many algae-resistant shingles include copper-containing granules for the same reason, which reduces black streaks. They are designed mainly for algae, so shaded slopes may still need moss control. See moss and lichen on roofs and black streaks and algae on roofs.