What is roof moss, and what does it do to a roof?
Short answer. Roof moss is a small, rootless green plant that grows in damp, shaded spots and anchors itself in the texture and joints of roofing. Over time it holds water against the roof, lifts shingles, loosens granules and lets moisture reach the decking, which leads to leaks and rot.
What roof moss is
Moss is a simple plant that absorbs water and nutrients through its leaves rather than roots. Tiny anchoring threads called rhizoids hold it in place. It spreads by spores carried on wind, so any roof that stays damp and shaded can grow it.
Why your roof has moss
- Shade from nearby trees, often on the north side.
- Leaves and pine needles trapped in valleys and along gutters.
- Low pitch or poor drainage that keeps water around.
- Georgia's humid weather and mild, wet winters.
What it does over time
- Year one: thin green fuzz in shingle joints. Mostly cosmetic.
- Next few seasons: cushions form along the bottom edges of courses, holding water and loosening granules.
- Later: shingle edges lift, seal strips break, and wind driven rain gets underneath.
- Long term: underlayment and decking stay damp, leading to leaks, rot and mold on the attic side.
It also sheds into gutters, causing overflows that rot fascia, and makes the roof slick and dangerous to walk.
How to get moss off a roof
- Apply a roof labeled moss killer on a dry day.
- Wait for it to brown and loosen.
- Remove it gently downslope by hand or soft brush, and let rain do the rest.
- Never pressure wash or scrape live moss.
Then prevent it with sunlight, debris removal and zinc or copper strips. See moss and lichen on roofs and trees and your roof.