A roof can look perfectly sound from the pavement and still be hanging by corroded nails. Nail sickness is the trade name for that condition. Each tile or slate is held to its batten by one or two nails, and when those nails rust, snap at the shank or work loose from the timber, the covering is no longer fixed to anything. The first sign is usually one tile that has slipped. The next is another, a month later, a few courses along. By the time the pattern is clear, much of the roof may be resting on friction and habit. This page explains the cause, how to tell it from other faults, and what to do.
What nail sickness actually is
The name is slightly misleading because the tile is not sick, the fixing is. Most pitched roofs are fixed by nails driven through a hole in the tile or slate into the batten below, or by tiles hanging on nibs and nailed in some courses. Over decades, those nails face moisture, condensation and temperature swings. The ones that were made of plain or poorly protected steel corrode. The rust swells, flakes and thins the shank until it snaps, or it eats the nail head and the tile slides off.
It is most associated with slate, where a single nail through the head of each slate carries the whole load. But it affects clay plain tiles nailed in alternate courses, and any tile on a roof fixed with old iron or inadequately galvanised nails. Concrete interlocking tiles can show it too, because the clips and nails behind them are the same age as the roof.
Think of it as a failure of a component, not of the covering. The tiles may have decades left. The nails behind them are what is running out.
Why the nails corrode
Several things work on a nail over the years. Condensation in a poorly ventilated roof space leaves the underside of the battens damp for months, and a nail in a damp batten corrodes from the inside out. Acid from smoke and from rain on an industrial-era roof attacks unprotected steel. Salt on a coastal roof accelerates the same process. Mortar and certain timbers, particularly oak, are aggressive to some metals. And in a roof with no underlay, which describes many pre-war houses, the nails sit exposed to whatever blows in under the tiles.
The quality of the nail matters most. Early roofs were fixed with cut iron or wrought iron nails, which rust. Later, galvanised steel nails slowed the process but did not stop it, because the zinc coating wears or is damaged when the nail is hammered in. Modern roofers use stainless steel, aluminium or copper nails because they are not subject to the same corrosion, and the current tiling standard expects fixings of a type suited to the site.
How to spot it
You can often see it from the ground, with binoculars if needed. The signs build up in a recognisable order.
- Slipped tiles or slates. A tile sits lower than its neighbours, leaving a gap at the top or a visible patch of batten.
- Tiles in the garden or gutter. Whole, unbroken tiles that have dropped off, often after wind, with no obvious impact damage.
- Rust streaks. Orange staining under the tail of a tile or slate on the roof, or on the underside seen from the loft.
- Clinking or rattling. A tile that moves or rattles under light wind because it is no longer pinned.
- Pattern. Slips that spread across a slope rather than affecting one spot, or that return after each repair.
Inside the loft, a torch tells you more. Look at the underside of the tiles and the battens. Orange rust powder on the batten under a tile, nail points showing through, or nails that have lost their heads all indicate corrosion. Our guide to signs a tiled roof is failing places these among the other warning signs, and the pitched roofing hub gathers the rest of our tiled-roof guides.
What it is not
Several other faults look like nail sickness and need different fixes. Telling them apart saves money.
Wind lift can strip tiles from a roof whose nails are perfectly sound, if the tiles were not clipped on an exposed site. Our answer on why roof tiles lift in the wind sets out that cause. Frost damage can crack and flake clay tiles so that they break away, which is a different failure again. Rotten battens can let go of good nails because the timber holding them has softened, and the guide to roof battens explains why. And movement in an old roof structure can pull tiles out of place with nothing wrong in the fixings. Each of those can produce slipped tiles, and only a close look at the nails tells you which you have.
For slate roofs the picture is similar, with its own detail. Our slate pages on slipped and cracked slates and on slate hooks versus nails cover the slate-specific repairs.
Which roofs are most at risk around Basingstoke
Age and construction tell you where to look. Older slate and clay roofs on pre-war terraces and villas in the older parts of town and the surrounding villages are the classic case, because their fixings were laid before galvanising was reliable and they may never have had an underlay to shield the nails. Roofs from the interwar and postwar building booms were often fixed with galvanised steel, which lasts longer but is not permanent, and many of those roofs are now old enough for the zinc to have worn through. Roofs of the 1960s and 1970s estates carry concrete tiles with fixings that are now the age of the house. Newer roofs fixed with stainless steel or aluminium are the least likely to be affected.
Exposure and ventilation add to the picture. A roof with no ventilation and a damp loft will corrode nails faster than a dry, ventilated one of the same age. A roof under trees stays damp longer. A house with a boxed-in eaves that blocks the air path can speed things up. None of these is certain, and a roof of any age can be sound, which is why we look at the nails themselves rather than guessing from the date.
What a repair visit involves and what it costs
A local repair is short work for a roofer. We reach the area by ladder, tower or scaffold, lift the tiles around the slip, replace any broken ones, refix the sound ones with new corrosion-resistant nails or clips and make good. Access is a large part of the cost. One UK cost guide, written for slate, reports labour at £100 to £250 for one slate, a few pounds of material (£5 to £25) on top, and £300 to £800 more where a tower or scaffold is needed. Tile repairs follow a similar pattern, and these are typical UK ranges and not Beacon prices. The fixed quote you receive follows the survey, so the number reflects your roof.
Because access is the bulk of the cost, it makes sense to fix everything found in a single visit. A series of small repairs, each needing a tower, costs more than one thorough visit.
Repair or relay: how we decide
The answer depends on how far the condition has spread. If only a few nails have failed, the problem is local, and we replace the slipped tiles and refix them with corrosion-resistant fixings. A sound roof with a handful of slipped tiles does not need to be torn off.
If the corrosion is across a slope, or across the roof, repairs become a treadmill. You fix a tile this winter and another lets go next winter, and the cost of repeated call-outs and scaffold adds up. At that point the sensible option is to strip the affected area, check and replace the battens, refix the tiles or slates with stainless or aluminium nails, add clips where the site demands them, and relay the covering. The tiles themselves can usually be reused if they are sound, which makes the job far cheaper than a new roof. Our guide to tiled roof repair costs covers the numbers.
| What we find | Usual answer | Why |
|---|---|---|
| A few slipped tiles, nails sound elsewhere | Local repair with new fixings | The fault is confined and the rest holds |
| Rust staining across one slope | Strip and refix that slope | Failures are likely to continue there |
| Nails corroded roof-wide, battens sound | Strip, refix with new nails, reuse tiles | The covering is sound, the fixing is not |
| Nails and battens both failing | Relay on new battens and underlay | Refixing to weak timber would not hold |
Temporary fixes and what to avoid
A slipped tile is worth securing quickly, because a tile that falls is a hazard below, and an exposed gap lets water onto the underlay. Several quick fixes exist. A tile clip can hold a slipped tile in place. On slate, a strip of copper or lead, known as a tingle, can hook over the slate tail to hold a slate with a failed nail. Sealant under tiles is not a fix. It hides a moving tile, traps water and often makes the next repair harder.
These temporary measures are meant to bridge a gap until a decision is made. They do not cure corrosion elsewhere on the roof. Never go onto a roof yourself to push tiles back. Roof tiles crack under a person's weight, nail sickness means they may not be pinned at all, and falls from roofs are a real hazard. Our answer on whether you can walk on roof tiles explains why not.
Preventing it on the next roof
If you are re-roofing, nail sickness is largely preventable at the point of fixing. Ask your roofer what the nails and clips are made of, and make sure the answer is stainless steel, aluminium or copper rather than plain galvanised. Check that the roof space is ventilated so battens stay dry, and that the underlay is properly laid. A roof laid to current standards should not develop nail sickness for a very long time.
What we do when we survey
We look at the nails as well as the tiles. We take photographs of any corrosion, check a sample of fixings in the loft and at the roof, and note whether the pattern is local or general. Where repair does the job, we say so and quote for it. Where a relay is justified, the report shows why, with pictures from your own roof. The price comes in a fixed written quote, and our workmanship guarantee runs for ten years in writing. If you have spotted slipped tiles, the quickest step is a call to 01256 213956 or a message on WhatsApp.
