What are algae-resistant shingles?
A portion of the granules contain leachable copper ceramically coated, designed to protect against discoloration from algae on the roof. This does not protect from moss growth but does slow the growth. Moss likes to feed on algae and any other debris on the roof. Most manufactures offer a 5- to 10-year warranty against algae growth; 3M (scotchgard TM) offers a 20-year warranty.