The short answer
They are the same material. Cotswold District Council's technical guidance notes that the southern end of its area favours the word tile, while the northern end says slate. Both describe thin limestone pieces hung on oak pegs in graded courses. When you ask a roofer for a quote, describe the roof by its make-up, not by which word you favour.
One roof covering with two names
Stone slate and stone tile both mean the thin pieces of split limestone that cover traditional roofs across the Cotswolds. The district council's old technical guidance for owners observes that people in the southern part say tile and people in the northern part say slate. That is a local habit of speech, nothing to do with the product itself.
You will also meet the word slate used alone, plus older trade names for individual pieces. Those are explained on our page about Cotswold slate names. If a surveyor, estate agent or planning officer uses one word and your roofer uses the other, they are almost certainly describing the same roof, and a short chat clears it up.
Building trades are full of local words for one thing, and the same is true of walling and floor finishes. The sensible habit is to describe the material itself, and to ask the person you are speaking to which stone and which method they have in mind.
What the two words do not describe
It helps to know what a stone slate is not. It is not Welsh slate, a hard, dark, evenly split rock laid flat and regular. It is not a clay tile, which is baked in a kiln. It is not a concrete tile, even though some concrete products carry a Cotswold-style name on the packaging. The natural stone is an oolitic limestone, and the geology behind it is explained on our page on Cotswold slate geology.
Sandstone slates from other regions are a further trap. Policy that the council reproduces cautions that a limestone roof should not be patched with sandstone, nor the reverse, since the two stones age and drain in quite different ways. So when a quote mentions stone slate, ask which stone it is, where it came from and whether it is new or reclaimed.
Where you are on the map
The council's guide places the tradition in a long belt that begins at Chipping Campden and reaches as far as the outskirts of Bath. The limestone does not stop at a county boundary, so villages around Cirencester, Fairford, Malmesbury and the Cotswold edge share a family of details. What differs from place to place is the local word, the size of the stone and sometimes the angle of the slope.
For a house within reach of Swindon, the practical point is simple. Whatever your village calls the covering, a repair or relay has to match what is there already, using the same stone, the same oak pegs and the same pattern of graded courses. The page on stone roof pitch explains how the steep angle of these roofs shapes the whole design, and why a shallower roof would need a different approach.
Why the exact name matters on paper
On a planning form, a listed building application or an insurance schedule, a vague description can cause trouble. Writing natural stone slate or natural stone tile, along with the type of stone, leaves no room for a reconstructed product to be slipped in unnoticed. Reconstructed stone slates are concrete, with a stated minimum pitch of 30 degrees and a stated laid weight, and under that same policy they do not suit historic buildings.
The same applies to repairs. A patch made with the wrong stone, or with a concrete lookalike, shows up within a season or two as a different colour and a different texture. Naming the stone and its source in a quote protects the roof, and it adds a few lines to the paperwork that nobody regrets, and it protects you if the work is ever questioned.
If you are arranging insurance, the wording can affect the rebuild figure too. Check how your policy describes the covering, and keep a dated photograph of the roof on file. The piece on how long a stone roof lasts sets out what to expect from the genuine article, which in the right conditions can outlast the people who roof it.
What to say when you ask for a quote
Describe the roof in plain terms. Say that it is stone, name the village, and say whether the slates hang on oak pegs. Mention any listing or conservation area. Offer a rough date for the building if you have one, and mention slipped slates, stains inside or any earlier repairs you know of. Two photographs from the garden are plenty, one showing the whole roof and one showing the worst patch.
Should the house carry a listing, mention it first. Listed status affects what can be done and who must agree, and we would rather plan for that than discover it halfway through. The conservation area and the council that covers your village also matter, since Swindon Borough Council, Wiltshire Council and Cotswold District Council each handle their own planning decisions.
The survey then fills in the detail, and the written quote reaches you with pictures of your own slopes. We lean towards whichever option cures the problem with least disturbance, be that a patch repair, a partial relay or a full strip. Read the overview on Cotswold stone roofing to see how we work, and look at graded courses to see how a stone roof is laid from eaves to ridge.