Short answer
- Slipped or broken slates, corroded nails (“nail sickness”) and failed lead flashings are the most common causes of slate-roof leaks.
- Repairs should reuse sound slate and match the size, type and colour of the existing covering; lead and lime details should be repaired in kind.
- Like-for-like repairs in matching materials often do not need listed building consent, but it is sensible to confirm with your local planning authority first.
- Work at height is high risk, so checks beyond ground level should be left to a roofer with safe access.
Common faults on traditional slate roofs
Most slate-roof problems start at the fixings and details rather than the slate itself. Over decades, iron nails corrode and lose their grip, so slates slip or slide out of course — often called “nail sickness”. Wind-driven Scottish rain then finds the gaps, and a single slipped slate can let water track along the timbers some distance from the visible stain.
Lead is the other common weak point. Flashings, soakers and valley linings work hard at junctions with chimneys, abutments and roof valleys, and split or fatigued lead is a frequent leak source on older roofs.
- Slipped, cracked, delaminating or missing slates
- Corroded nails or failed fixings causing repeated slippage
- Split, lifted or fatigued lead flashings and valleys
- Open or eroded mortar at ridges, hips and verges
- Damp staining near chimneys, valleys and roof junctions
Matching slate, lead and lime details
On a traditional roof, the repair should be sympathetic to what is already there. Sound salvaged slates can often be reused, and replacements should match the size, type and colour of the existing covering so the roof keeps a consistent appearance and weathering line.
Lead details should be repaired or renewed in appropriate gauges, and mortar bedding at ridges and verges is usually best repaired with a suitable lime-based mortar rather than hard cement, which can trap moisture and crack. Sealant coatings or spray-applied foams are not a substitute for sound slating and can damage slate and roof timbers.
Permissions on listed and conservation-area buildings
Many traditional Scottish roofs are on listed buildings or sit within conservation areas. Like-for-like maintenance in matching materials may not need listed building consent, but altering the roof’s appearance, materials or detailing can, and unauthorised work to a listed building can have serious consequences.
Before work begins on a listed or conservation-sensitive property, it is sensible to check with your local planning authority and to use materials and methods suited to a traditional roof.
Safe access and survey-led repair
Roof work is treated as high risk, and proper planning, competent people and suitable access equipment are part of the job. Checks beyond a safe ground-level or window view should be left to a roofer with appropriate access rather than attempted from a ladder.
A survey should record the condition of the slate, fixings, lead, mortar and roof structure, note access constraints, and set out repair priorities with photographs — so the work that follows is specified around the actual defects, not a guess.
- Safe access assessed before any close inspection
- Slate, fixing, lead and mortar condition recorded with photos
- Repair priorities and likely causes set out clearly
Useful Scottish references
- Engine Shed: slate roofs Scottish slate roof guidance on inspection, repair, reuse and permissions.
- Historic Environment Scotland: maintenance of traditional buildings Scottish maintenance guidance covering water ingress, roof coverings, gutters, chimneys and inspection tips.
- Historic Environment Scotland: listed building consent Scottish guidance on listed building consent, like-for-like repair and planning authority checks.
- HSE: roof work Roof work guidance covering safe access, roof edges, fragile surfaces and method statements.
