How do you eliminate roof moss for good?

Part 1: Kill it

Apply a moss treatment labeled for asphalt shingles on a mild, dry day, following the label's rain-free time. Zinc-based products last longer; soap-based products work faster. Wait for the moss to brown and loosen, which can take days to weeks.

Part 2: Remove it gently

Brush the dead moss downhill with a soft brush on a pole, rinse with a garden hose at normal pressure or let rain do it, and clean the gutters afterward. Never pressure wash or scrape upward under shingle edges.

Part 3: Remove the reasons it grew

• Sunlight: trim overhanging limbs and thin dense canopy over the roof. This is the single most effective long-term step. See trees and your roof.
• Debris: keep valleys, the area behind chimneys, and roof-to-wall corners free of leaves and pine straw. See pine needles and leaves on the roof.
• Drainage: keep gutters flowing so the lower courses dry out.
• Metal strips: zinc or copper strips near the ridge release small amounts of metal with each rain, discouraging regrowth below them.

Keep watch

Check the shaded slopes each fall and spot-treat new growth while it is thin. On a roof near the end of its life, moss elimination is mostly about protecting what remains; at replacement time, trimming and drainage fixes give the new roof a head start. See moss and lichen on roofs for more on prevention.