How do you clean algae off a tile roof?
Know your tile
- Glazed clay: smooth and fairly resistant to growth. Algae usually sits in dirt along the edges.
- Unglazed clay: porous, holds moisture, and grows algae and moss readily.
- Concrete tile: porous with a colored surface coating. Pressure washing can strip that coating and expose bare concrete that then grows algae faster.
The soft wash method
- Wet and cover plants below the roof.
- Test the cleaner on a small, hidden area to check for color change.
- Apply with a low-pressure pump sprayer, working in sections.
- Give it the dwell time on the label, keeping it from drying.
- Rinse with a garden hose at normal pressure.
Walking on tile
Tile breaks under point loads. If someone must walk the roof, they should step on the lower part of each tile where it overlaps the tile below, distribute weight, and avoid ridges and unsupported edges. Many pros clean tile entirely from ladders or lifts for this reason.
After cleaning
Look for cracked or slipped tiles, which let water reach the underlayment. On tile roofs, the underlayment usually wears out long before the tile, so a roof with recurring leaks may need the tiles lifted and the underlayment replaced rather than more cleaning. Concrete tile can be resealed after cleaning to slow regrowth. Tile is less common in Georgia than shingles, so choose a cleaner or roofer with real tile experience.
See moss and lichen on roofs and black streaks and algae on roofs.