How do you treat moss on a roof, and how often?
Short answer. Treat roof moss by applying a roof safe moss killer on a dry day, waiting for the moss to die and loosen, then gently removing it from the top down without scraping granules off. On moss prone shaded roofs, a preventive treatment once or twice a year, or zinc or copper strips near the ridge, keeps it from returning.
Stage 1: kill it
- Choose a product labeled for roofs and your roofing material, such as a zinc sulfate, potassium soap or bleach based treatment.
- Apply when the roof is dry and no rain is forecast for the period the label specifies.
- Protect plants and keep runoff out of streams and storm drains.
Stage 2: remove it gently
Dead moss turns brown or yellow and loosens over days to weeks. Rain washes much of it off. What remains can be pushed off by hand or with a soft brush, always working downslope so you never lift the shingle edges. No pressure washer and no metal scrapers.
Stage 3: prevent it
- Trim branches to bring sun and airflow to the roof.
- Keep valleys, gutters and the roof surface free of leaves and pine needles.
- Install zinc or copper strips just below the ridge.
- Choose algae resistant shingles at replacement.
How often to treat
- Active moss: one full treatment, then a follow up if patches survive after a month or two.
- Prevention on shaded slopes: once or twice a year, often in fall and spring, or as the product label directs.
- Sunny roofs with no history: usually no routine treatment, just inspect yearly.
Moss is most common in Georgia on north slopes under hardwoods and in the mountains. See moss and lichen on roofs and trees and your roof.