In damp, shaded climates like coastal BC, moss thrives on roofs. Left alone it holds moisture against the shingles, lifts them, and shortens roof life, so removing it and keeping it away protects your roof.
Remove it gently
Never pressure-wash an asphalt roof — it strips the protective granules and does more harm than the moss. Instead, gently brush or scrape moss off working downward, or apply a moss-killing roof treatment and let it die and wash off over time.
Treat and prevent
Roof-safe moss treatments kill remaining moss. To keep it from returning, install zinc or copper strips near the ridge — rain carries trace metal down the roof that inhibits moss growth. Trimming overhanging branches lets sun and air dry the roof.
Address the cause
Moss loves shade and trapped moisture. Improving sun exposure, clearing debris that holds water, and maintaining gutters all reduce the damp conditions moss needs.