The short answer
Cotswold stone slates are oolitic limestone: thick, heavy and laid in diminishing courses, at roughly 1,000 kg per 10 m². Welsh slate is thinner, laid in even courses, and regularly lasts over a century. Stone suits the steep traditional pitches. Swapping one for the other changes both the look and the load, so on older roofs we keep like for like.
Weight and what holds the roof up
Cotswold District Council's 2000 note gives a stone slate roof a load of about 1,000 kg to every 10 m². That is a hefty covering, and the timbers and walls beneath were built to carry it. Natural slate is far thinner, so a slate covering on the same frame would weigh a good deal less. We have no confirmed slate weight to quote, so this page does not give one.
The difference matters for two reasons. The Planning Portal requires approval when a new covering is 15 per cent or more heavier than the old, and Approved Document A treats a significant rise in loading as a reason to check the structure. A frame built for stone is happy with something lighter. A frame built with light timbers cannot simply be handed stone.
It also means a stone roof is not something to treat casually. Rafters that have borne that load for generations can sag at their feet, and a roof that moves opens its courses.
How the two look and how they are laid
Stone breaks out as few large slates and many small ones, which is why a Cotswold roof is laid in diminishing courses. The council note puts the biggest slates at around 600 mm, sometimes 750 mm, in a double course along the eaves, and the smallest at a mere 150 mm near the top. The result is a roof whose texture changes from bottom to top, with an irregular surface and a soft, uneven tail line.
Welsh slate is another proposition. It is cut to size, so courses run level, and the face is flatter and finer. The Cupa Pizarras pitch data we rely on lists slates of 500 mm and 600 mm, which shows how regular the product is.
Fixing differs as well. Stone slates hang from the batten on one or two oak pegs, while slate is normally nailed or hooked. For a feature that picks up the stone texture around an opening, see our answer on dormers on Cotswold stone roofs.
Pitch, life and cost compared
The figures come from different sources and different years, so read the table as a rough guide, not a ruling.
| Point | Cotswold stone slate | Welsh slate |
|---|---|---|
| Typical pitch | Traditionally 47° to 55°, not a minimum (council, 2000) | Minimum 20° at moderate exposure with a 500 mm slate (BS 5534, via Cupa Pizarras) |
| Typical life | 100 years with regular maintenance, possibly 200 or 300 (council, 2000) | Regularly over a century (MyBuilder, 2026) |
| Re-roof cost | About £160 to £210 per m² for stone slate generally (Checkatrade, 2026) | £140 to £180 per m² installed (MyBuilder, 2026) |
The stone cost is not Cotswold-specific, and the council gives no minimum pitch for stone, so the pitch row sets a traditional range against a published minimum. Treat every figure as typical, dependent on exposure and workmanship, and never as a promise.
Care decides both lifespans. A yearly scrape, the council suggests, can double a stone roof's span. Slate wants a look after storms as well.
Why swapping one for the other is a decision, not a saving
On a modern house with no protection, either covering is open to you, subject to the structure and your planning position. On an older Cotswold building the choice narrows. English Heritage policy, printed in the council note, calls substitutes for stone unsuitable on historic buildings and asks for replacement slates to match the originals in rock, colour and dimensions. Welsh slate is a different rock from Cotswold limestone, so by that test it does not match.
Replacing like with like normally escapes planning permission, as the look is not materially changed. Changing from stone to slate does change the look. If the house is listed, you would need listed building consent, and in a conservation area the council's planning officers are the people to ask. Stroud District has 41 conservation areas.
Look at the roofs around you too. In a village built of stone, a slate roof usually reads as a later alteration, and many owners end up wanting stone back.
Choosing, and what happens next
Three things drive the decision: what the building was designed for, what its structure can carry, and what officers and neighbours will accept. With an existing stone roof, the starting point is nearly always to keep stone. Our answer on how many old stone slates can be reused shows how much of your own stone may go back up.
If someone is offering a manufactured alternative, read why such products are often turned down in reconstituted and artificial stone slates.
A survey from us comes with pictures of your own roof, followed by a written quote covering scaffold, strip, covering, labour, waste and making good. Steep lanes and terraced hillsides are planned into the figures from the start. Our workmanship guarantee lasts 10 years and is written down. Ring 01453 933613, message us on WhatsApp, or use the enquiry form, or go back to Cotswold stone roofing.
What each covering asks of the owner
A stone roof rewards attention. Scraping moss, checking pegs, keeping lime sound at the ridge and verges and replacing slipped slates quickly are the routines that carry it past a century. The jobs are small but they are regular, and they need a roofer who knows how stone behaves.
Welsh slate is more forgiving of a lapse, though not immune. Slipped slates, corroded fixings and failed flashings still let water in, and a slate roof that is left alone will not look after itself either. What changes is the vocabulary: nails and hooks instead of pegs, even courses instead of graded ones, and lead flashings in place of mortar fillets in many places.