What is nail fatigue on a slate roof?

Two nails through holes near the head of each slate hold it to a timber batten. On older roofs, including many Victorian ones, those nails were commonly iron. Iron rusts wherever damp reaches it, and a roof is damp for much of the year, especially under moss and at the thinner, more exposed edges of a slope.

Rust eats the shank of the nail. Hidden under the slate above, the nail is never seen or painted, so corrosion carries on unnoticed. It swells, flakes and weakens until the nail snaps under the slate's own weight or a gust of wind, or until the thin shank pulls clean out of the batten. A nail that began as a firm fixing becomes a thread of corrosion. Once a few have gone, the weight moves onto neighbouring nails, which are just as old, and they follow.

That is why the word fatigue fits. Nothing has been struck or broken. The fixings have simply been worn out by time and moisture, in a roof whose slates are often still perfectly good.

All the nails on a slope were driven at the same time, from the same stock, into battens that have had the same weather. They age together. The first slipped slates are the weakest, but the rest are only a few seasons behind.

Wind accelerates it. A slate loosened by a rusted nail rattles, which fatigues the second nail, and a gust that lifts one slate can break the hold of the one beside it. After a stormy winter an owner can go from two or three slipped slates to several dozen. Our guide to how slates are fixed explains the nails, hooks and clips involved, and why modern copper or stainless nails are chosen for new work.

It also explains why tingles stop being useful. A strip nailed into the batten can restore one slate, but it cannot rescue the fixings around it.

The early warnings can be seen without climbing. Binoculars in the garden or a photograph from an upstairs window will show most of them.

• Slates sitting lower than their neighbours, leaving their lines uneven
• Gaps in a course, or a slate resting at a slant
• Whole patches of slipped slates, especially near the lower edge of the slope
• Pieces or whole slates in the gutter, on a path or in the garden
• Rust-coloured streaks on slates, a sign that iron fixings beneath are corroding
• Tingles that have themselves loosened or stretched

Any one of these can be a one-off. Two or three together on the same slope usually are not.

Inside, damp patches on the upstairs ceilings or daylight showing in the loft are signs that water is already getting through the gaps. A roofer can also lift one or two slates and look at the nails, which shows the rust directly. Lifting a slate to look is a quick test, and it tells us whether you are dealing with a few loose slates or a slope that has run out of life. We would rather find that out for you before you spend money on repairs that will not last.

What a survey adds

From inside the loft we can see whether the underside of the battens is dark with damp, whether nail points show through, and whether daylight shows between slates. That view often settles the question in minutes.

When the nails across a slope are spent, there are only two honest answers: patch each fault as it appears, or renew the fixings in one go. Patching leaves a roof that keeps failing, each repair needing access of its own. MyBuilder's 2026 guide puts five to ten slates at £150 to £350, a range that can be spent several times over in a few years of piecemeal visits. Repeated visits also mean repeated access, and a scaffold hired more than once is the quickest way to overspend.

Renewing the fixings means stripping the slope, sorting the slates, discarding the cracked ones and relaying the sound ones on new battens and corrosion-resistant fixings. The slate is the expensive part and it is often reusable, as our answer on reusing old slates describes. MyBuilder's guide gives £100 to £180 per m² for slate installed: £100 to £130 for Spanish slate and £140 to £180 for Welsh.

Once the survey is done, the quote covers scaffold, stripping, slate, battens, underlay, labour and waste, together with the photographs that show why the work is needed. Checkatrade's 2026 guide puts scaffold for a roof at £700 to £1,300, which is why a large slipped patch is better dealt with in one go than in three visits. For the cost of the small jobs, see what one slate costs to replace.

Because the work keeps slate as slate, the roof looks as it did, and the waste leaves with us when the job ends. A tidy site matters on a terrace or a shared lane, where skips and stacked slate quickly get in the way of neighbours. Our workmanship guarantee runs for 10 years, in writing. The wider options are on our slate roofing page, and the number is 01453 933613.