Possible causes
- Nail fatigue — the fixings corrode and slates slide out
- High winds lifting edges
- Frost damage to older or porous tiles
- Foot traffic from other trades or aerial installers
Warning signs
- Slates or tile fragments in the garden or gutter
- Visible gaps or lines out of place on the roof
- New damp patches after windy weather
Typical solutions
- Replacing individual slates using copper or lead tingles
- Matching reclaimed slates or tiles where possible
- Re-roofing a slope if slipping is widespread