The short answer
Repair a slate roof when the problem is confined to a few slates, one slope or one lead detail, and the nails and battens around it are sound. Re-slate when slips keep returning in new places, because the nails are giving way across the roof as a whole. The deciding test is the condition of the nails and battens, not the age of the slate.
The rule that settles most cases
Slate rarely wears out first. The things that hold it do. Each slate hangs from nails driven into timber battens, which are the timber laths running across the rafters, and in older work those nails were frequently iron. So ask what is holding the slate up rather than how old it is. The real test is whether that support is failing in one spot or all over.
If a single slate has slipped and the ones around it are firmly nailed, you have a local fault. Swap that slate, look over the ones beside it, and the roof carries on. If you replace a slate and a different one lets go beside it the following winter, the fixings are the problem, and patching will only chase the next failure across the slope.
That second pattern has a name, nail sickness, and our page on nail sickness covers how it develops. One affected slope can be dealt with on its own. Several affected slopes point towards a full re-slate.
What a repair can sensibly cover
Repair works well when the cause is specific and can be named. Patching suits faults of this kind:
- One or two slipped or cracked slates on an otherwise tight slope, usually from a fallen branch, a stray footstep or a single rusted nail.
- A split in a lead flashing. A flashing is the lead fitted where the roof abuts a chimney or wall, to keep water out of the joint. It can be renewed without touching the slate beside it.
- A failed valley or hip detail. A valley is the inside angle between two slopes, where rain gathers in a lead or slate channel.
- Storm damage to a defined area, where the slate surrounding it is sound.
Typical UK figures for small jobs are modest. In MyBuilder's 2026 repair guide, minor work like a small leak or a few missing tiles runs to roughly £100 to £300. Your own fixed price follows our survey. The common jobs are set out on our slate roof repairs page.
When patching has run its course
Several signs together tell you a roof has moved from repair to renewal. Any one of them alone may not.
Slips on more than one slope is the clearest. Slates that flake, turn soft or crumble at the nail holes are another, because that is the slate itself ageing and no new nail will cure it. Battens that are dark, damp or crumbling at the ends are a third, since a nail cannot hold in soft timber. Daylight visible from the loft, or an underlay that has gone brittle or is missing altogether, means water can get past the slate with nothing behind it to stop it.
Roofers also look at how many tingles are on the slope. A tingle is a narrow metal strip that grips the tail of a slate which has lost its nail. A few are normal. A slope covered in them has been patched many times, and the last patch is rarely the final one. What counts as too many is discussed on our slate tingle page.
How the money compares
A repair is cheaper on the day, but it is not always cheaper over the life of the roof. Each visit carries its own cost for access, and where the work is above the first floor, scaffold becomes a recurring item. MyBuilder's new roof guide gives scaffold at about £1,125 on a typical house. Pay for that several times across several repairs and the arithmetic starts to change.
A full re-slate in natural slate is priced per square metre. The same guide prices natural slate at £100 to £180 a square metre installed: Welsh £140 to £180, Spanish £100 to £130. Treat these as national averages from a cost guide rather than an Empire quote, because a real figure depends on the roof's size, shape, access and how much of the existing slate can be reused.
That last point matters. When a sound roof is stripped, the good slates are graded, stacked and relaid over new battens and underlay, fixed with copper or stainless nails. The slate you already own becomes part of the answer. Our re-slating guide explains the stages, and the choice of source is covered in Welsh versus Spanish slate.
What the regulations add
A repair that touches a small area does not usually need Building Regulations approval. Planning Portal guidance treats a small re-covering as exempt: approval is not normally required if under 25 per cent of the building envelope and under 50 per cent of the roof is affected. Above those limits approval is required, and the roof insulation value may have to be raised.
A new covering weighing 15 per cent more than the old one, or heavier still, needs approval plus a structural check, so swapping slate for something heavier is never a casual decision. If the job is notifiable, we explain the rules that apply and handle the building control paperwork.
Listed houses, and roofs that face the street in a conservation area, call for contact with B&NES planning ahead of any work, whether you repair or re-slate. A change of slate type is the point to raise first.
How we decide on a real roof
Our survey covers the roof from outside and the timbers from inside the loft. We lift a few slates to see how the nails have fared, check the battens from below for staining and softness, and photograph your roof so you can check our findings against the images. Then we say which path suits it, and why.
Where repair works, we repair. A roof that can be patched sensibly should not be torn up for the sake of a bigger job. Where a re-slate is the right answer, the price is set down in writing before work begins, and we say how many of your existing slates we expect to reuse and where they will go. Our slate roofing service covers both routes.
Weighing it up yourself first? A simple check helps. Stand across the road and look along each slope for gaps, tabs and sagging lines, then look in the loft for damp timber and light. Write down what you see slope by slope. That list is more useful to a roofer than a general worry that the roof is old.
