Stone slate or stone tile: what's the difference?

In April 2000 Cotswold District Council published a technical note for people who own or look after stone roofs. On the question of terms it is brief: stone tile is the usual word further south and stone slate further north. That is a remark about speech, not about stone. Whichever word you hear from a builder, an estate agent or a neighbour, the covering being described is hand-split limestone laid in overlapping courses.

The muddle comes from borrowing. A true slate is metamorphic rock, like the Welsh and Spanish slate sold across the country, which splits along flat planes formed under pressure. A tile is a fired product. Cotswold stone is neither, so both older words fit it loosely. We use stone slate on these pages because that is the term the council's guidance applies to the roofs themselves, and we treat stone tile as a perfectly good synonym when a customer, a surveyor or a planning officer prefers it.

The council's note identifies two parent rocks behind Cotswold roofing stone. Both are oolitic limestones, meaning they are built from tiny rounded grains of lime. One is Forest Marble, which is split by hand, and the slates cut from it are known as presents. The other is Stonesfield Slate, which is frost-split: the quarried stone was left exposed so that winter freezing prised it apart into thin layers.

Those are the facts that matter if you are asking what you have on your roof. The real question is which limestone, how it was split and how thick the pieces are. A roofer reading a slope looks at colour, the texture of the face, the thickness at the tail and the lengths in each course. Those clues separate genuine split limestone from a lookalike, and they tell us what any replacement stone has to match.

Where you will see it

The guidance says the covering survives across the region, running between Chipping Campden at the northern end and a point near Bath in the south. Stroud lies inside that sweep, so the stone roofs on cottages, barns and chapels around the Five Valleys belong to one tradition, whatever label the village gives them.

Policy from English Heritage, quoted in that same note, wants replacement slates to resemble the old ones in rock, shade, surface, length and depth. It adds that sandstone must never take the place of limestone, or limestone that of sandstone. That is the line that counts on a repair or a re-lay. A quote that says stone tile in one place and stone slate in another is not a warning sign. A quote that never says which stone, from which source and in what lengths deserves questions before any work starts.

The policy also turns down man-made substitutes, whether concrete tiles, reconstituted stone or resin-fibre slate, wherever a building has historic standing. Should your home be listed, or lie within a Stroud District conservation area, expect the council to look hard at any switch of covering. Our answer on consent for a stone re-roof sets out what to ask the planning team.

When you collect quotes, expect the vocabulary to wander between firms and even between people at one firm. A written quote should still give you the same information whichever word it favours.

• The stone type, such as Forest Marble or a named quarry product, and whether it is new or second-hand.
• The lengths by course, in the old names or in plain millimetres.
• The way the slates are held on, and what the battens are made of.
• What happens to the ridge, hips, verges and valleys.
• A written price for scaffold, stripping, materials, labour and rubbish removal.

The old size names are a different matter, and an entertaining one. They describe where a slate sits on the slope, not what the material is called. Our answer on cussoms, followers and short cocks covers that vocabulary.

If you are buying or insuring a house with a stone covering, write down what each document calls the roof, then ask a roofer to confirm what is really up there. Valuation reports, listing descriptions and insurance schedules all pick different words, and a mismatch is common and harmless. What matters is that the description of the building and the description of the work agree with each other.

The covering is heavy, about 1,000 kg for every 10 m² on the council's figure, so the structure underneath has to be sound whatever the covering is called. It is also held on in a particular way, with wooden pegs over battens, and our answer on oak pegs explains the reasoning. Pitch belongs to the same system, and why stone roofs are so steep shows how.

At a survey we photograph the slopes, look at the underside from the loft and record the stone and the fixings. A written quote follows, and we guarantee the workmanship for ten years, in a document you keep. To follow the rest of a stone job through, our Cotswold stone roofing page describes it, from the first survey to the final clear-up of the site.