Stone can outlive generations of owners, yet it will not do so unattended. Individual slates slip as their fixings age, crack as water freezes in the bed of the stone, or delaminate in layers. Each one is a small hole in the roof, and in stone the hole is often found first as a stain on a ceiling.
Small jobs are the subject here, not whole-slope work. It covers how a repair is diagnosed, how a slipped or broken slate is replaced so that it matches the courses around it, what happens when pegs and battens have perished, and how valleys are mended. For the larger job of rebuilding a failed slope, see our guide to re-laying a Cotswold stone roof. The service as a whole is on our Cotswold stone roofing page.
Slipped or broken: working out which you have
From the ground the two faults look alike, though they are mended differently. A slipped slate is a sound slate that has dropped down its batten because its fixing has failed. Its tail sticks out below the line of the course, and a gap opens at its head. A broken slate has cracked or split, so that part of it has fallen away or is hanging loose.
Delamination
Stone slates are split from beds of limestone, and the layers can separate with age and frost. The council's guidance describes Stonesfield Slate as frost-split, which is a reminder that frost works along the bedding. A delaminating slate loses its face in flakes, thins, and eventually fails. Flakes in the gutter are a clue.
What we check beyond the slate
Each slate has a cause. Behind a slipped slate there is often a failed peg, a rotten batten or a worn hole; behind a broken one, a knock, frost or a slate too short for its place. Swap the slate without finding the cause and the same repair comes round next winter. The loft gets a look as well as the outside, since stains on the boards show where water has been entering.
Replacing a slipped slate
If the slate is sound, re-fixing it is usually the right repair. The slates around it are eased up carefully. The slipped slate is lifted, its hole is checked, and if it is worn, it is re-holed higher up in sound stone. A new peg is cut and driven through, and the slate is set back in its place so its tail sits on the line of the course.
Why length matters
On a graded roof each slate belongs to a band of lengths. A slate re-holed higher becomes slightly shorter in the roof, so it may be better placed one band up. Fitting a slate into the wrong course leaves a thin lap or a tail hanging below the line. Our guide to diminishing courses is the background to this. We only mention it here because it is the reason a stone repair takes longer than it looks.
Access
Stone slates should not be walked on without proper boards, because a footstep can crack them. Repairs at height are done from a ladder with a roof ladder or from a tower, and where a repair needs scaffold for safe access, that is allowed for in the quote.
Replacing a broken slate with a match
A broken slate cannot be mended and has to be replaced. The source of the replacement matters. The 2000 council guidance carries an English Heritage line that favours new stone slates and keeps old ones with the building they left. For a repair, the best source is often the roof itself: slates set aside from an earlier job or recovered from a section being re-laid. Our guide to reclaimed or new stone slates sets this out.
What a match means
A good replacement agrees with its neighbours in stone type, colour, surface, length and thickness. Cross a sandstone with a limestone roof and you have made a new fault, and sawn slates are listed as a poor choice in the same guidance. Patching with a tile or manufactured slate shows from the road and may fail early.
A repair that does not match the course around it will draw water and the eye. Take photographs before and after, and ask what the replacement slate is.
If the matching slate has to be ordered, it adds a lead time. The survey tells you how long, and the roof is made watertight in the meantime.
Perished pegs, rotten battens and worn holes
The traditional fixing, as the council's guidance describes it, is a split-oak peg pushed through a hole near the slate's head so that it hooks over the batten. Timber in a damp roof space eventually decays, and a decayed peg lets a good slate drop. When slates are sliding in groups, pegs are among the first things we examine.
Spotting the pattern
If one slate has slipped, it is probably a single fault. If several in a band have slipped, or slates slip again soon after being re-fixed, the cause is likely to be the pegs, or the battens they rest on. A rotten batten has to be replaced, and that means lifting the slates above and below it. Our answer on oak pegs explains the fixing in more detail.
When to stop repairing
A repair to a failed section stops making sense when the same fault appears across the slope. Chasing slipped slates one by one costs more over time than a re-lay, and the council's guidance records about half the slates as commonly perished once a roof is stripped. When repairs begin to repeat, we tell you plainly and price the alternative, so you can compare.
Valley work: where repairs often start
Valleys take the run-off from two slopes in one channel, so the water load is high and faults show up fast. The traditional Cotswold valley is the swept valley, with the courses turning the angle in stone. Cut pieces, which the guidance names bottomers, lie-byes (also side skews) and skews, do the turning, and none of them can be bought off a shelf.
Repairing a swept valley
A repair replaces the cut slates that have cracked or slipped, and renews the battens beneath if they have rotted. Because the pieces are cut to the angle of the valley, we make them from matching stone. Our guide to swept valleys explains how the pieces are formed.
Lead valleys
Valleys built with lead, whether mitred tight or left open, are the cheaper option in the guidance, which advises against them. Turning a swept valley into a lead one is not a repair we would suggest. Where a lead valley already exists, the lead is renewed to a suitable code. Leadworx lists Code 5 for general and vertical work and Code 6 for large roofs, so the code follows the size of the run.
Chimney abutments and wall junctions are a further source of leaks on stone roofs, and flashings there are checked at every repair visit.
Chimney junctions, verges and other weak spots
Slates are only part of the picture. A stone roof leaks most readily where the stone stops: at a chimney, against a gable wall, along a verge or round a rooflight. These junctions rely on lead, mortar or a stone ridge, and each of them ages faster than the slates around it.
Chimney and wall flashings
Lead flashings at a chimney stack are dressed into the stone and over the slates. If the lead lifts, splits or loses its pointing, water runs behind it and shows up as a stain on a ceiling far from the stack. We check these at every repair visit. Leadworx names Code 4 as its standard choice for ordinary flashings, and MyJobQuote gives £150 to £250 for patching a chimney flashing, as a national figure.
Verges and ridge
On the gable edge, the last slates are bedded in mortar and can loosen as the mortar weathers. At the top, a stone ridge sits on a bed of mortar, and since BS 5534:2014, ridge and hip pieces get mechanical fixings on top of the bedding. A ridge that has shifted needs lifting and re-bedding, not a smear of mortar over the crack.
Why we look at the whole roof
Fixing the visible hole and leaving a tired junction beside it only moves the leak. A repair visit lets us take in the whole roof, and what we find goes into the notes sent with the quote.
Making a roof safe while repairs wait
Sometimes the right repair cannot happen at once. The matching slate has to be sourced, the weather is poor, or a listed house has to go to the council first. Meanwhile water has to stay out.
Temporary measures
For a leak, the first step is to stop water getting in. That might mean refixing a slate loosely, laying a membrane under a loose area, or sheeting a section. These are stop-gaps and we call them that, with notes and photographs so that the permanent repair can be planned. A leaking roof or storm damage gets our attention before routine work.
What you can do from inside
Look in the loft after heavy rain. A damp patch on a rafter or a drip onto boards tells us where to start, and a photograph with the date helps. Do not go onto a stone roof yourself; slates crack underfoot and the pitch is steep.
After a storm
High winds can lift slates, shift ridge pieces and bring down branches. Check the garden and the paths for fallen fragments, then send us the photographs. Loose slates above a path or door are a safety matter and should be reported straight away.
Upkeep after the repair: moss and the gutters
Moss and lichen sit in the bedding of the slates, hold water against the stone and add weight. A roof scraped once a year, says the council's guidance, could last twice as long. Hand scraping is the traditional method. Our answer on scraping moss off a stone roof covers timing and technique.
Cost of keeping the roof dry
MyBuilder's roof cleaning guide, updated in 2026, gives manual moss scraping at £5 to £10 per m² and cautions against pressure washing on fragile tiles. That is a national figure for roofs in general. A stone roof is not delicate in the same way, but it is brittle at the edges, so we scrape by hand.
Gutters and downpipes
A blocked gutter backs water up under the eaves courses. We clear the run when we are on the roof and report anything we see. Cast iron and heavy gutters on stone houses are also checked at their brackets.
Listed roofs, costs and what you get in writing
If your house is listed, the repair may need consent. Stroud District Council is clear that listing protects a building at every grade, and the Planning (Listed Buildings and Conservation Areas) Act treats unauthorised works that alter a listed building's special interest as an offence. A repair matched exactly to the old may still merit a word with the conservation team. Our guide to listed stone roofs covers the steps; please ask Stroud District Council's planning team first.
National repair prices
MyBuilder's slate roof cost guide, updated in 2026, gives £60 to £120 to replace a single slate, and £150 to £350 for five to ten. In Checkatrade's repair guide, natural slate repairs at £150 to £220 per m², ex VAT and without access. These are for slate in general; stone work, being heavier and pegged, rarely comes in below them.
Survey photographs of your own roof come first, then a written quote. Water is stopped first. Workmanship carries a 10-year guarantee, written down, and the site is left tidy.