Fault diagnosis
Nail Sickness Explained: Why Victorian Slates Slip in Patches
Nail sickness is the corrosion failure of a slate roof's iron fixings, which releases sound slates in scattered patches while the slate itself remains serviceable. Compare the pattern on your own slopes against nail sickness, then book a survey to settle it. Nail sickness produces slips across multiple slopes at once; a localised cluster indicates a different cause.
Nail sickness is corrosion failure of the iron fixings, not of the slate. Storm damage looks similar from the ground and is a different job, so the pattern is what separates them.
- How long the fixings last
- An iron nail runs 60 to 100 years before corrosion releases the slate.
- How long the slate lasts
- Natural slate reaches 100 years, outlasting its own original fixings.
- What a tingle does
- It refixes one slate without lifting the course. It is a holding repair, it is visible, and it does nothing for the adjacent fixings.
What is nail sickness?
Nail sickness is the corrosion failure of the iron nails fixing a slate roof. The nails rust through and lose their grip, releasing individual slates while the slate itself stays sound. Roofers also call it nail fatigue or nail rot.
How do you know it is nail sickness and not storm damage?
Nail sickness produces slipped slates scattered across several slopes over months. Storm damage produces a concentrated group of losses on one slope on one date. Scatter and repetition identify nail sickness; concentration and a single event identify wind.
The service life of the iron nail is 60–100 years before corrosion releases the slate. Natural slate lasts up to 100 years, exceeding its original fixings.
- Diagnostic pattern: scattered, not localised; multiple slopes; accelerating rate
Why do the slates outlast their nails?
Natural slate resists frost and water for a century or longer, while the iron nails holding it corrode within sixty to a hundred years. The covering therefore reaches the end of its fixing life long before the end of its material life.
A tingle is a metal clip refixing a single slate without lifting the course.
- Tingle limitation: a holding repair; visible; does not address adjacent fixings
Can nail sickness be repaired with tingles?
No, not permanently. A tingle is a metal clip that refixes one slipped slate without lifting the course, and it holds that slate only. Every adjacent nail continues corroding, so slips recur and accumulate across the slope.
A strip and relay means slates lifted, sorted, refixed on new battens and membrane with non-ferrous nails; a copper / aluminium nail is the non-ferrous replacement that prevents recurrence.
What does a strip and relay involve?
A strip and relay lifts every slate, sorts the sound units from the broken, renews the battens and underlay, and refixes the reusable slates with non-ferrous nails. Seventy to eighty-five per cent of slates are typically reusable.
- Victorian terrace relevance: Balsall Heath, Sparkbrook, Handsworth, Moseley — Welsh slate over cut timbers
- An iron nail corrodes, releases slate, exposes underlay and admits wind-driven rain.
The decision is a whole-roof judgement.
Which Birmingham roofs are affected?
Victorian and Edwardian terraces built with Welsh slate over cut timber roofs are affected, concentrated in Balsall Heath, Sparkbrook, Handsworth, Moseley and Harborne. Properties built between 1870 and 1914 now sit at or past their original fixing life.
- A tingle refixes slate but does not remedy nail sickness.
- A strip and relay reuses sound slate on a new batten with non-ferrous fixing.
Getting the roof assessed
- Nail sickness is diagnostic of a whole-roof fixing failure, not of a slate wear.
7 symptoms route to their own diagnosis: A damp patch on an upstairs ceiling, Water coming in with no visible damage outside, Slates or tiles slipped out of line, Water spilling over the gutter, Damp in the loft with no rain, A ridge line that dips in the middle and Moss across the slope.
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