What roof moss cleaner and preventer works best?
Short answer. The products that both clean and prevent moss usually rely on zinc compounds, such as zinc sulfate, or on potassium salts of fatty acids, which kill the moss so it dries and releases from the shingles. Apply on a dry, mild day, let it work for days or weeks rather than scraping, and keep moss from returning with zinc or copper strips near the ridge and more sunlight on the roof.
How the main types work
- Zinc-based products: zinc sulfate solutions and granules kill moss and leave a residue that slows regrowth, but runoff can stain and harm plants and ponds.
- Fatty acid soap products: potassium salts of fatty acids act quickly and are gentler on surroundings, with less lasting prevention.
- Bleach solutions: sodium hypochlorite kills algae and surface growth fast but does little long term, can harm plants and is hard on metal flashing and gutters if not rinsed.
- Oxygen bleach cleaners: sodium percarbonate products lift stains and help with algae more than thick moss.
Application tips
- Check the shingle manufacturer's cleaning guidance first; some warn against specific chemicals.
- Wet and cover plants below, and rinse them again afterward.
- Apply with a garden sprayer from a ladder or the ground where possible. Moss-covered roofs are slick.
- Let the dead moss loosen and wash off with rain. Do not scrape or pressure wash, which strips granules.
In Georgia
Moss shows up mostly on shaded north slopes under hardwoods and pines, where the roof stays damp. Trimming limbs to let in sun and air is the most durable preventer. Robust Roofing's guide to black streaks and roof cleaning covers what not to do. Also read moss and lichen on roofs and black streaks and algae.