What is the best roof moss and mildew remover?
Short answer. Look for a product labeled for roofs that lists both moss and mildew, typically based on sodium hypochlorite (bleach), quaternary ammonium compounds, or potassium salts of fatty acids. Bleach based soft washes clean mildew and algae fastest, while quaternary ammonium spray and leave products handle moss and mildew more slowly with no rinsing.
Common active ingredients
- Sodium hypochlorite (bleach): kills mildew, algae and moss on contact, and whitens stains quickly. Needs plant protection and rinsing.
- Quaternary ammonium compounds: the base of many spray and leave cleaners. Kill moss, mildew and algae gradually, with rain rinsing them off over weeks.
- Potassium salts of fatty acids: soap based moss killers. Fast on moss, less effective on stains.
- Zinc sulfate: strong on moss, little effect on mildew stains, and can leave light residue.
- Sodium percarbonate (oxygen bleach): gentle cleaner for mildew and algae, weaker on established moss.
Matching product to problem
- Mostly black streaks and mildew, a little moss: bleach soft wash.
- Mostly moss with some mildew: a quaternary ammonium or soap based moss product, then a soft wash if stains remain.
- Plants close to the eaves: oxygen bleach or spray and leave products.
Check before you buy
- The label says it is safe for your roofing material.
- Application instructions do not involve pressure washing.
- Your shingle manufacturer does not prohibit the ingredient.
Why mildew keeps coming back
Mildew on a roof lives on organic debris. If leaves and pine straw keep collecting, it returns. Clearing debris matters more than the product. See pine needles and leaves on the roof and moss and lichen on roofs.