The short answer
Repair when the fault is contained: a few slipped slates, one tired flashing, a cracked valley. Re-slate when nails, battens or underlay are giving way over a full slope, because patching then only relocates the leak. Slate is often reusable, so the cost of re-slating is mostly labour, felt, battens and scaffold, not new slate.
Why slate roofs fail before the slate does
MyBuilder's slate roof guide (updated August 2026) gives 80 to 100 years or more for slate laid well. Checkatrade's guide, last updated in September 2026, gives a wider range of 50 to 200 years. Slate itself is a durable stone. What wears out first on an old roof is everything holding it up: the iron or steel nails, the timber battens, and the felt or underlay beneath.
Nails corrode and the slates slide. Battens rot where water has crept in. Felt, if there was any, goes brittle and stops doing its job. From the pavement a roof may look sound while these hidden parts are a few storms from letting go. Our page on delaminating slates covers the other way slate itself can fail, where it flakes in layers.
Signs that a repair is enough
A repair suits a roof with few faults, all of them contained. Typical cases are three or four slipped slates after a gale, a cracked slate where a ladder was leant, a worn flashing at a chimney, or one failed valley. In each, the surrounding slates sit firmly, the nails are sound, and the leak stops when the fault is fixed.
A simple test is to ask what the cause is. If the cause is a single event or a single component, a repair deals with it. Replace the broken thing and the roof goes back to how it was. Our guide to slate valleys shows what a local valley repair involves.
Where a repair cures the problem we advise one, though a bigger job would pay us more.
Signs that re-slating is the better answer
Re-slating makes sense when the same problem keeps coming back or when it is widespread. Look for slipped slates in many places across a slope, slates that slide down within a year of being fixed, nails that snap as slates are lifted, rotten or sagging battens, and daylight through the roof in the loft. A rule of thumb that tradespeople use is the slipped-slate count: if you can see many slipped slates from the ground, the nails across the slope are likely to be failing, not just those ones.
Underlay is the other trigger. Many older roofs have none, or old bitumen felt that has perished. Re-slating lets the roofer lay new membrane and fix new battens, then hang the existing slates with fresh nails. Done properly, that gives an old roof a new working life using most of the original slate. The reslating guide sets out the sequence.
What each route costs
National guides give the order of magnitude. MyBuilder's roof repair guide, updated August 2026, lists minor repairs at £100 to £300, moderate repairs at £500 to £1,000 and major repairs at £2,500 or more. Its slate guide puts re-roofing in slate at £100 to £180 per square metre installed, with Welsh slate at £140 to £180 and reclaimed slate at £110 to £150.
| Route | Typical national range |
|---|---|
| Minor repair, a few slates | £100 to £300 |
| Moderate repair, a patch of the slope | £500 to £1,000 |
| Re-slate with new slate, per m² | £100 to £180 |
| Scaffolding, standard two-storey house | £850 to £1,200 |
Treat these as national ballparks. A high roof needs scaffold for either route, so a string of small repairs can be dearer overall than one job. The survey ends with a quote on paper.
Matching slates and keeping the look
On a street of similar houses, re-slating with the original slates keeps the roof looking right. Slates that come off in good condition go back on, and broken ones are replaced from the stock of reclaimed slate or from new slate chosen to match the colour and size. If you want to mix new and old, the new slates are normally laid on the less visible slopes. Our page on matching roof slates explains how.
If the house is protected, whether listed or inside a conservation area, like-for-like work is the safe approach, and listed building consent can be needed. Raise it with Swindon Borough Council's planning officers first.
If the roof is a good candidate for re-slating, the weight of slate may also matter. Heavier new slate on an old frame can mean extra checks, and the Building Regulations apply if the covering is heavier by 15 per cent or more, as the Planning Portal puts it.
Making the call with evidence
Ask for photographs. A good survey shows the underside of the slates, the nails, the battens and the felt, and tells you how many slates are loose. From that you can see whether the problem is local or spread. Our pros and cons of slate page may help you weigh the longer-term choice.
Our survey explains the cause, with photographs, and the written quote covers the lightest fix that cures it. A repair if a repair will do; a re-slated slope, with the reasons shown, if not. Workmanship on the finished job is guaranteed for ten years on paper, and we tidy up before leaving.
To start, phone 01793 626096 or message us on WhatsApp. The slate roofing hub lists related work, and slate valleys shows one common local repair. If you want a second angle on cost, the slate versus tile comparison sets slate against other coverings.