What is nail sickness on a slate roof?

Each slate hangs from nails driven through two holes into the batten. The nail heads sit under the slate above, so they stay mostly dry but they are never entirely so. Rain driven under the slates, condensation and air moving through the roof keep the metal damp for much of the year. Nails made of plain steel, or with a thin zinc coat, corrode. The rust swells, the nail thins, and eventually the shank snaps just below the head or the head breaks off.

The slate does not usually fall at once. It sits on the slate below, held by friction and the weight of the course above, until wind or frost nudges it and it slides. The first sign is often a single slate, a few courses down from the ridge, that has shifted a little out of line with its neighbours. Left alone, it gives the slate above it less support, and the fault travels up the slope one course at a time. Our page on slate roof repairs explains the first-line fixes for such a case.

The pattern is what tells it apart. Slipped or missing slates appear in several places across the same slope, often in rows, and the roof has been repaired more than once for the same fault. Slates look intact but sit loose when a roofer lifts them gently, and the nail stubs are brown, flaky or missing. In the loft you may find rust flakes or fragments of nail on the insulation and the rafters, and daylight where a slate has gone.

It also helps to know the age of the roof, and whether a previous owner or roofer ever re-fixed it. Older roofs were often fixed with nails that were adequate for their day but are now at the end of their life, and a roof that has stood for several decades without trouble can begin to show the problem rapidly once corrosion reaches a certain point. The slate itself may be perfectly good, which is why the roof is worth saving by relaying it.

Re-fixing a slate with a tingle, a lead or copper strip nailed to the batten and folded over the slate's tail, is a quick repair that works well where the neighbouring slates are solidly fixed. On a sick roof, the batten may be holding corroded nails on all sides, so the tingle holds one slate while the next slips. You pay for repeated visits and the next gale finds the next weak nail. Our page on slate tingles sets out where they belong.

The cost trap is easy to fall into. A single slate repair belongs in the minor repair band of £100 to £300 in MyBuilder's roof repair guide, updated 21/08/2026. Four or five of them in a few winters add up to a sum that goes a long way towards a reslate, and the roof is not any stronger at the end.

If the slipping is spread, the sound answer is to take off the slates, discard the battens that are rotten, fit new underlay where it has failed, and relay the existing slates, supplemented with new or reclaimed ones where some have broken. The new fixings are copper, stainless steel or aluminium alloy nails, chosen because they do not rust. Where a slope needs relaying, it makes sense to deal with worn lead flashings and valleys while the slope is open, since reaching them later means lifting slates twice.

If the slates themselves are delaminating or cracked, a reslate with new slate is more sensible than reusing them. The survey with photographs decides which. MyBuilder prices a slate re-roof at £100 to £180 per m² as a national guide. Your own figure comes as a written total after we have inspected the slopes. Our page on the cost of replacing a single slate explains the other end of the scale.

Slipped slates can fall without warning, so keep people and cars away from the area beneath, and stay off the slopes yourself. Slate is brittle underfoot and the surface is slippery when wet. Where rain is already getting in, we put leaks first on the list, and the opening step is a temporary repair that stops the worst of it until the roof can be dealt with properly. Heavy rain and wind are the moments when a loosened row is most likely to move, so do not leave a known problem through the autumn.

Photographs of the slope from the ground, any slates you find in the garden and a note of when earlier repairs were done help us understand the roof before we visit. A handful of nails collected from the gutter or loft floor tell us a good deal, as rust that has eaten the shank and left the head intact is the classic sign. The survey then shows the nails, the battens and the underlay. The job we put forward is the minimum that truly cures the problem. Workmanship is covered by a 10-year guarantee in writing, and when we leave, the debris goes with us. Our page on waterproofing a slate roof covers the layers beneath the slate, and slate roofing gives the full service.