How long does a roof moss treatment last?
Short answer. A single moss treatment usually protects a roof for a few months to about a year, depending on the product and how shady and damp the roof is. Zinc or copper strips near the ridge provide longer, ongoing protection for the area below them, while heavily shaded roofs may need a yearly treatment.
By type of treatment
- Soap based (fatty acid) treatments: kill moss quickly but break down fast, so regrowth protection is short.
- Zinc based treatments: leave zinc on the surface that keeps working with each rain, often protecting for a season or longer.
- Leave on quaternary ammonium products: work slowly and may keep growth down for months.
- Zinc or copper strips: installed under the ridge cap or near the top of the slope, they release metal with every rain for years, protecting the area below them. Effectiveness fades farther down long slopes.
Why moss comes back
Treatment kills what is there; it does not change the conditions. Shade from pines and hardwoods, debris in valleys and slow drying north slopes will grow moss again. In Georgia, regrowth usually shows in the cool, wet months.
Making protection last
- Trim branches to let in sun and air.
- Clear needles and leaves from valleys and from behind chimneys.
- Keep gutters flowing so water does not sit at the eaves.
- Add zinc or copper strips if moss is a repeat problem.
- Treat again at the first sign of green, before mats form.
When treatment is not enough
If moss has lifted many shingle edges or the roof is near the end of its life, repairs or replacement may be the better investment. See moss and lichen on roofs and the Georgia roof maintenance checklist.