How do you prevent moss on a roof, and which prevention methods work?
Short answer. The methods that prevent roof moss best work in combination: zinc or copper strips near the ridge, a periodic gentle treatment labeled safe for asphalt shingles, regular removal of leaves and needles, and trimming trees for more sun. Avoid pressure washing and scraping, which damage shingles more than the moss does.
Methods compared
- Zinc or copper strips: installed just below the ridge cap with a few inches exposed. Rain carries metal ions down the roof, which discourages moss and algae. They work best within several feet below the strip and are least effective on long slopes. Nails should be placed under the course above or sealed.
- Moss treatment sprays: products labeled for roofs can kill existing moss and slow regrowth. Apply in mild, dry weather, protect plants below, and let dead moss loosen and wash off with rain rather than scraping it.
- Debris removal: clearing leaves and pine needles from valleys and gutters a few times a year removes the damp layer moss roots in.
- Tree trimming: more sun and airflow is the most durable prevention on heavily shaded Georgia lots.
- Algae resistant shingles: copper containing granules resist the dark algae streaks common in the Southeast. They help, but they are not a guarantee against moss.
Methods to avoid
- Pressure washing: blasts off protective granules and can force water under shingles.
- Scraping or wire brushing: tears shingle edges and breaks seal strips.
- Strong, undiluted bleach: can harm plants, gutters, and some roofing materials; follow the shingle manufacturer's cleaning guidance.
- Walking on a mossy roof: moss is slippery and dangerous, especially on steep slopes.
When moss is a sign of something bigger
Thick moss lifts shingle edges, holds water against the mat, and can let wind driven rain under the shingles. If moss has been there for years, have the shingles checked for curling, granule loss, and soft decking before treating. See moss and lichen on roofs and black streaks and algae on roofs.