What Is Nail Sickness on a Slate Roof?

A slate hangs from the batten on two nails driven through holes near its top edge. The next course overlaps and hides the heads, which keeps the nails out of sight and also keeps them damp. Over many winters a steel nail in a damp, half-sheltered spot corrodes. The shank thins, the head weakens, and eventually the nail lets go or the slate slides over its head.

That is nail sickness. The slate itself may be perfectly good: the CoRC roofing materials guide says slate can last 100+ years if well maintained, while the iron nails holding it often cannot. This mismatch explains why a roof full of sound-looking slates can still shed them one at a time.

Old roofs were often fixed with whatever nail was to hand, and a roofer who looks at the underside of a loose slate can usually tell what it was made of and how far gone it is. For a refix, ask which nail is proposed and why it will outlast the slate. A fixing that gives up long before the slate does wastes a good covering.

From the garden, look for slates that have dropped a few centimetres so their tails sit below the course line, giving the roof a ragged, uneven look. Gaps where a slate has gone altogether are easier to see, and so are slate pieces on the lawn or in the gutter. Binoculars help. Do not climb up to check; slate is slippery and breaks underfoot.

Inside, a torch may show daylight through a gap, rust-brown streaks on the underside of slates, or slivers of slate lying on the insulation. Rusty nail fragments on the loft floor or in the gutter are a strong hint that the fixings are going.

Pattern says more than count. A handful of slates slipped after a storm, in one corner, points to local damage. Slates sliding across a whole slope, or low down near the eaves, suggest nails have corroded everywhere. A roofer lifts a slate or two in different places to see the nail heads, then reports back with photos. Our answer on why roof tiles slip covers causes on tiled roofs, which differ.

For a limited number of loose slates, the usual repair is a tingle, a thin copper or lead strap that is fixed to the batten and folded up around the slate's tail to hold it from slipping again. Our answer on slate tingle repair explains how that works and where it ends. Tingles fit well when slates and battens are sound and only a few fixings have gone.

Once nails are failing across a roof, repeated tingle repairs become a string of small bills while the roof keeps getting worse. At that point the better buy is to strip the slope, check the battens and underlay, and fix the slates again with corrosion-resistant nails. Good slates are reused where they are sound, and broken ones are replaced.

A roofer can only decide after seeing how many nails have gone and in what pattern. If the written quote is for re-slating, it should say whether your own slates will be reused, what the new nails are made from, and how the finished roof is fixed to BS 5534. We photograph the fixings we uncover, and you can compare the nails with the slates yourself. Our natural versus man-made slate answer helps if you are weighing up a different covering.

Slate roofs need a minimum pitch, and BS 5534 indicates 20 degrees as the floor for natural slate. Cupa Pizarras adds that hook fixings should stay off pitches under 25 degrees, so a shallower roof needs a different method of fixing. A roofer should measure your pitch before choosing how to refix.

Checkatrade's June 2026 repair table gives £150 to £220 per square metre for natural slate repairs in Spanish slate, without VAT and for areas up to three square metres. Read that as a yardstick for a small patch only. Re-slating a slope is priced by its area and by how the roof is reached, once a survey has been done. VAT and scaffolding should both be named in whatever quote lands on your doormat.

Three questions are worth putting to any roofer. Are the existing slates being reused or replaced? What will the new nails or hooks be made of? How will the work meet BS 5534? The answers show if the offer on the table is a short-term patch or a proper refix, and a good roofer will be glad to be asked. Our pitched roofing page covers whole-roof work, and the final figure is set in writing after the roof has been looked at closely.