Nail sickness — when a slate roof starts shedding
In short
Nail sickness is the corrosion of the original iron nails holding a slate roof on, and it is why an old roof starts losing slates from everywhere at once. It cannot be patched out of, because every remaining fixing is the same age and in the same condition — so the honest answer is usually a strip and re-lay.
Also called: Slates keep slipping · Nail fatigue · Roof shedding slates · Slate nails rusted
Signs you need this
- Slates slipping repeatedly, from several different areas
- Rust-coloured staining running down the slates below nail lines
- Reddish grit or nail fragments in the gutters
- Slates that move when pushed gently from inside the loft
- Visible corrosion on nail heads seen from the roof space
- A history of patch repairs that keep needing repeating
Victorian and Edwardian slate roofs were fixed with iron nails. Iron in a damp roof space corrodes, and after a hundred-odd years the nails reach the point where they no longer hold the weight of a slate. They fail one at a time, over years, in no particular order — which is exactly what makes it so recognisable once you know the pattern.
That pattern is the diagnosis. A single slipped slate is bad luck. Slates coming off two or three a year, from different slopes, with rust-coloured staining running down beneath the nail positions and gritty red residue in the gutters, is nail sickness. From inside the loft it is unmistakable: the nail heads are swollen and rusted, and a gentle push moves slates that should be solid.
The reason it matters so much financially is that it defeats patching. Every repair is sound — the slate goes back properly, the tingle holds — and the roof carries on shedding, because the other four thousand nails are exactly as old and exactly as corroded. Homeowners often spend several hundred pounds a year for five or six years before somebody tells them plainly that they are maintaining a roof that has ended.
The remedy is a strip and re-lay. The slates themselves are frequently still excellent — good Welsh slate outlives its fixings comfortably, and a roof at a hundred years old may have eighty percent of its slates fit to go straight back on. So the job is: strip, sort and set aside the sound slates, renew the battens, fit a breathable membrane, and re-lay using the salvaged slate plus reclaimed matching stock to make up the shortfall. That is both cheaper and better-looking than new slate throughout, and in a conservation area it is usually the answer the planners want too.
The Building Regulations get involved at that scale. Stripping more than a quarter of the covering makes it notifiable under Part L, which brings a duty to improve the roof's insulation to current standards where feasible, and requires the work to be certified — either through Cheshire East Building Control or by a roofer registered under a Competent Person Scheme. That is not a reason to avoid the work; it is a reason to make sure it is included in the quote.
The one genuinely good piece of news is that nail sickness is slow. It is not an emergency and nobody should let it be sold as one. A roof at this stage typically has a year or two of manageable decline, which is enough time to get proper quotes, arrange the money and pick a season — and doing it in spring rather than in a January panic saves real money.
What the job covers
- Inspection from inside the loft as well as outside
- A straight answer on whether patching still makes sense
- Strip, sort and salvage of sound slates for re-laying
- New treated battens and a breathable underlay
- Reclaimed matching slate to make up the shortfall
- Building Regulations notification and certification
What it costs
We don't publish a price for this yet, because a number pulled out of the air is worse than no number at all — your roofer has to honour it. On roofing it would also be close to meaningless: access is often the biggest single factor, and it varies enormously house to house. You'll get a firm price for your actual job when they ring you back, before any work starts. The quote itself is free and there's no obligation either way.
Common questions
Can it be repaired rather than replaced?
Individual slates can always be refixed, and if money is tight that is a legitimate way to buy a year. But it does not stop the process — the remaining nails are the same age and in the same state. The honest position is that patching a nail-sick roof is renting time, and past a certain point the rent exceeds the mortgage.
Do I have to buy all new slate?
Usually not, and you should not want to. On a typical hundred-year-old Welsh slate roof a large majority of the slates come off sound and go straight back on. Reclaimed matching slate makes up the difference. The result costs less than new slate throughout and looks correct rather than new, which matters in a conservation area.
How urgent is it?
Not urgent. It is a slow failure, usually giving a year or two of gradually increasing nuisance before it becomes a real problem. That is enough time to get several quotes and choose when to do it. Anyone treating nail sickness as an emergency to be fixed this week is selling, not diagnosing.
Will I need Building Control involved?
Yes, because stripping more than 25% of a roof covering is notifiable under Part L of the Building Regulations. It goes through either a building notice to Cheshire East or a roofer registered with a Competent Person Scheme who can self-certify it. Either way you should end up with a certificate — keep it, because a buyer's solicitor will ask.
Need this doing in Macclesfield?
Tell us the job and it goes straight to our local roofer — one call back, usually the same day. Free quote, no obligation.