The short answer
Yes. Cotswold slates are limestone, and water that soaks into the stone and then freezes can prise its layers apart, so slates flake, split or lose their faces. Frost also helped to make some of them, because Stonesfield slate was split by freezing. A roofer can tell whether a flaking slate is a one-off or a sign of a tiring roof.
Frost made the slates and can undo them
The geology explains it. Cotswold District Council's 2000 technical guidance names two oolitic limestones used for roofing, the Forest Marble and the Stonesfield Slate. Stonesfield stone was frost-split: quarried blocks were left exposed so winter freezing opened them along their natural beds, after which they could be divided into slates. Forest Marble, by contrast, was split by hand soon after quarrying, with no frosting needed.
That history shows what a limestone slate is: a stone with natural layers and pores that take in water. Rain soaks in, a hard frost turns the moisture to ice, and the ice expands. After many winters this can lift the surface of a slate in thin sheets or crack it along its bed. Our page on Cotswold slate geology describes the stones in more detail.
None of which makes stone roofs fragile. Plenty of old limestone roofs have come through many winters, and the ones that fare best are those where small faults are fixed before frost can exploit them. The district council's booklet judges that a roof kept in order can comfortably pass a hundred years, and perhaps a great deal more. Frost is one of the ordinary forces a roof lives with, and one that stays dry underneath and clear of moss copes better.
How frost damage shows
Delamination is the main sign. A slate attacked by frost may show a face that has peeled away in thin plates, leaving rough, thinner stone behind. After a cold snap you may spot grit and flakes of stone lying beneath the eaves or caught in a gutter run. Another sign is a slate split across its width, which opens a gap for water to pass straight through.
Other signs are subtler. A weakened slate may slide off its peg or nail and leave a hole in the course. Moss and lichen keep the surface damp for longer, though a light covering does no harm by itself. Our page on stone roof abutments covers the junctions where damp often appears first.
Up in the loft, watch for damp patches beneath the slates, dark timber, and drips after a hard frost followed by a thaw, since thawing is when trapped water finally escapes. A single flaked slate is a repair job. Plenty of flaked slates on one slope suggest the stone there is nearing the end of its working life.
Why a cold, wet spell tells you so much
Watching a roof through a freezing, wet week teaches more than any amount of summer inspection. Water running where it should not, damp in the loft after a thaw, and fresh flakes on the ground all show where the stone is giving up. Winter exposes weak points that fine weather hides.
A roofer's look in the colder months is worth having, though weather has to allow it, since wet icy stone is unsafe to walk on and we will not do it. A roof that is already leaking is dealt with ahead of routine jobs, starting with making it safe. Pictures of what we find are supplied alongside the written quote, so you can follow the reasoning yourself.
Cotswold District Council's 2000 booklet notes that stripping often finds roughly half of an old roof's slates perished. Your roof will differ, but the observation explains why we count the sound slates before saying a slope can be patched. Our page on repairing or relaying a stone roof sets out how that choice is made.
Patching a few slates, or relaying
If damage is limited to a few slates, they are replaced with matching stone and any that have slipped are refixed. That is the minimal route to a dry roof, and it is what we advise where it works. The new stone should match its neighbours in kind, depth and colour, since English Heritage's policy warns against ever substituting sandstone for limestone slates or using the two together.
If the trouble is widespread, with slates delaminating right across a slope, repair after repair turns into false economy and the slope should be stripped and relaid. Sound slates are kept, perished ones are replaced, and the courses are rebuilt in order. That is a larger undertaking and needs scaffolding and settled weather.
Where rot, sag or movement shows beneath the stone, the timbers need attention as well. Our page on swept valleys is worth reading if your roof has them, since valleys gather water and are often where frost does its worst.
Cutting down the damage
The best protection is a roof that stays dry underneath and sheds water fast. Keep gutters and valleys clear so meltwater never sits against the stone. Refix slipped slates quickly, because any gap lets in water that freezes beneath its neighbours. Cut back overhanging branches, and take heavy moss off gently, never with a pressure washer, which can harm soft limestone.
The same booklet repeats an old belief that a stone roof gone over with a scraper each year might last twice as long, which points to the worth of steady care. A short check once the worst of winter has passed finds small faults before they spread.
To have someone look at your slates, ring 01793 626096 or send a few pictures by WhatsApp. The form on this site reaches us too. A visit ends with a written report, and the work itself comes with a 10-year workmanship guarantee in writing. Our Cotswold stone roofing page explains the service in full.