Nail Sickness in a Roof: Why Tiles Slip All at Once

Nail sickness in a roof is the failure nobody warns you about, because the thing that fails is the one part of the roof you cannot see. The tiles are fine. The battens are usually fine. The nails holding the tiles to the battens have rusted through, and once that has happened across one slope, no amount of putting slipped tiles back will fix it. That is why an old roof suddenly starts shedding tiles in groups after a gale, in a different place each time, having been quiet for forty years.

If you have had three separate roofers out to reinstate three separate slipped tiles in three separate areas, you are almost certainly paying to patch a roof that has already failed. Here is how to establish that before you spend anything else.

What is actually corroding

Older roofs were fixed with mild steel nails that were galvanised, meaning coated in a thin layer of zinc. The zinc protects the steel underneath by corroding first. It is a sacrificial coating, and it has a finite life.

Once the zinc is gone the steel goes quickly, particularly in the damp, oxygen-rich space just under the tile where condensation forms and dries repeatedly. Twenty to thirty years is a commonly quoted working life for a plain galvanised nail in a roof, and roofs fixed before the change to non-ferrous fixings are now well past it. What is left is a nail shank so weakened that it snaps at the batten face when the wind lifts the tile.

The critical point for a homeowner is that this is a whole-roof, age-related failure, not a localised defect. Every nail on that slope went in on the same day, from the same box, and is corroding at the same rate. The ones that have let go are simply the first.

The signs that tell you it is nail sickness

You can build a strong case from the ground and the loft, before anyone puts up a ladder.

Tiles slip in different places, repeatedly. One slipped tile is a slipped tile. Three or four in different areas over two or three winters is a pattern, and the pattern is the diagnosis.

The tiles themselves are sound. Pick up what came off. If the tile is unbroken, unspalled and clearly reusable, the tile did not fail. Something released it.

Nails snap when a roofer lifts a tile. This is the confirmation, and any competent roofer will tell you unprompted. On a nail-sick roof the shank shears rather than pulling; the head and a stub stay in the batten and the rest comes away as rust.

Rust staining on the battens and underlay. From inside the loft, look up at the battens where they cross the rafters. Brown streaks running down from the nail positions, and rust-coloured marks on the felt or membrane below, are the corrosion products washing down.

Rust dust in the loft. On a badly gone roof, running a hand along a rafter or a stored box brings back a fine orange-brown deposit that is not ordinary dust.

If you want this confirmed properly, a survey is the cheap step. Our roof inspection and survey guide covers what a genuine inspection should include and what it should tell you.

Why patch repairs are money into a lost roof

A slipped tile repair fixes one tile with one new nail. It does nothing for the several thousand original nails on the same slope, every one of them the same age and in the same condition.

The economics are straightforward and uncomfortable. Each callout carries an access cost, and on anything above a bungalow that usually means scaffolding or a tower, which is the single biggest line on a small roof repair. Pay that four or five times over three winters and you have spent a meaningful fraction of a re-roof on work that leaves the roof exactly as vulnerable as it was. Our slipped roof tile repair cost page sets out what individual repairs involve.

The Society for the Protection of Ancient Buildings gives a useful rule of thumb for when patching has stopped making sense: consider full retiling once around one-fifth of the tiles have been reinstated, and factor in the state of the gutters and flashings at the same time. Once you cross that line, every further repair is spending against an asset you have already decided to replace.

The thing that changes the economics: your tiles are worth keeping

This is the part that surprises people, and it is the reason nail sickness is a better problem to have than a genuinely worn-out roof.

If the fixings failed and the tiles did not, the tiles are an asset. SPAB advises that when a roof is completely re-covered, the maximum possible number of old tiles should be re-used, either mixed with new ones across the whole roof or with the new tiles placed on the least visible slopes. On a handmade clay plain tile or a good natural slate roof, that salvaged material is worth considerably more than its replacement cost, and it is the reason the finished roof still looks like the building it belongs to.

Be realistic about the yield. Industry experience is that roughly half a roof’s tiles or slates typically survive a strip, because tiles cut to fit hips, valleys and abutments cannot go back and a proportion break during removal no matter how carefully it is done. Ask any quoting roofer what salvage rate they are assuming and what they will do if it comes in lower, because that assumption sits underneath the price.

One warning from the same SPAB guidance: avoid second-hand plain tiles bought in from other buildings. Match new tiles to the existing ones on type, colour, texture, size and thickness instead. Reclaimed tiles off an unknown roof are of unknown age and may be carrying exactly the fatigue you are trying to leave behind.

What a compliant re-roof gives you that the old one never had

A strip and re-tile is not just the same roof again. Fixing standards changed, and the new roof is materially better held down.

BS 5534, the code of practice for slating and tiling, now requires fixings to be non-ferrous or stainless steel, with grades 304 and 316 stainless, copper and aluminium alloy all acceptable. That is the direct fix for nail sickness: the new fixings do not have a sacrificial coating to lose.

Every single lap tile is mechanically fixed, with nails, clips or both. Natural slates are mechanically fixed with nails or hooks to the manufacturer’s specification.

Plain tiles get a defined nailing pattern. Nibless double lap plain tiles take two nails in every tile. Nibbed double lap tiles take two nails in each tile in at least every fifth course on rafter pitches below 60 degrees, and more on steeper or more exposed roofs.

Mortar alone is no longer allowed to hold anything down. The 2018 amendment withdrew reliance on the tensile strength of mortar bedding to resist wind uplift, which is why ridges and verges on new work are mechanically fixed dry-fix systems rather than bedded in sand and cement. If your ridge tiles are mortar-only and the mortar is cracking, that is a second age-related failure running alongside the first.

Battens must be factory graded and marked to the standard and fitted at no more than 22% moisture content. Old battens are usually stripped and replaced as a matter of course, which is a good thing, because a new stainless nail into a fifty-year-old batten that has gone soft around the old nail holes is not much of an improvement.

You will normally also get a new underlay, and modern breathable membranes behave very differently from the old bitumen felt. Our roofing underlay and membrane guide explains the choice, and clay versus concrete roof tiles covers what to specify for the new tiles you do need.

Building control and who signs it off

A full strip and re-cover is more than a repair, and it can bring the roof into scope as a renovated thermal element under Approved Document L, which may mean upgrading the insulation while the covering is off. That is worth knowing before the quote, because insulating at the same time is far cheaper than doing it later.

There are two routes. Apply to your local authority building control, or use a roofing contractor registered with the National Federation of Roofing Contractors under its Competent Roofer scheme, whose members can self-certify their own work. The second is usually quicker and avoids a separate application, and it is a reasonable thing to ask a contractor about when you are comparing quotes. Our guide to finding a good roofer covers the accreditations that actually mean something.

What to do next, in order

1. Collect the evidence. Photograph every slipped tile and note the date and the location on the roof. A pattern across two or three winters is the case.
2. Look in the loft. Rust streaks below the batten nail lines and orange dust on the rafters are strong confirmation.
3. Ask a roofer to lift and check. The question is not “can you put this tile back”, it is “when you lift a sound tile nearby, does the nail snap or does it pull?”
4. Get the salvage assumption in writing. What percentage of tiles does the quote assume can be re-used, and what happens if fewer survive?
5. Ask what fixings and battens are being used, and whether ridge and verge are going to dry-fix.
6. Decide about insulation now, while the covering coming off makes access straightforward.

Frequently asked questions

What is nail sickness on a roof? It is the corrosion failure of the nails holding tiles or slates to the battens. The zinc coating on old galvanised steel nails wears away, the steel beneath rusts, and the nail shank eventually snaps under wind load. The tiles slip while remaining perfectly sound themselves.

How long do roofing nails last? Plain galvanised steel nails are commonly reckoned to give twenty to thirty years in a roof before corrosion becomes a real problem, although exposure, ventilation and the local atmosphere all move that. Modern stainless, copper and aluminium alloy fixings, which BS 5534 now requires, do not fail this way.

Can nail sickness be repaired without a full re-roof? Not meaningfully. You can re-fix individual tiles, but every remaining nail on that slope is the same age and condition, so you are buying a short delay rather than a repair. Once you are reinstating tiles repeatedly in different areas, the sums have already moved in favour of stripping the slope.

Are my old tiles wasted if the roof is stripped? No, and this is the good news. If the tiles are sound they should be salvaged and re-laid. SPAB advises re-using the maximum number of old tiles when a roof is re-covered, mixing them with new or keeping new tiles to the least visible slopes. Expect roughly half to survive the strip, since cut tiles at hips and valleys cannot go back and some will break.

Does nail sickness affect slate roofs too? Yes, and it is the classic failure mode on Victorian and Edwardian slate. The slate itself is a fifty to over a hundred year material and usually outlasts its fixings comfortably, so a slipping slate roof is far more often a nail problem than a slate problem. See our slate roofing guide for the material’s own lifespan.

How can I tell nail sickness from storm damage? Storm damage is concentrated, sudden and usually explains itself: an exposed edge, a ridge, the windward slope, all in one event. Nail sickness is scattered and recurrent, hits different areas across successive winters, and leaves the tiles themselves intact. If a moderate gale takes tiles off a roof that has stood through worse, suspect the fixings.

Is it worth insulating at the same time as a re-roof? Almost always. The access is already paid for, the covering is off, and a full strip may bring the roof into scope as a renovated thermal element under Approved Document L anyway. Doing it as a separate job later means paying for access twice.