Can sandstone slates replace limestone ones?

The wording sits in the council's April 2000 technical note for owners and occupiers, which prints English Heritage's sourcing policy in full. The policy expects replacement slates to track the originals on five points: rock type, colour, surface, length and depth. It then adds a single flat line that answers this page's question: sandstone and limestone slates must never be exchanged. Because the current heritage body's own technical page could not be opened, we cite this only as English Heritage policy as reproduced by the council in 2000.

Two neighbouring rules sit beside it. Fresh-cut stone is favoured over salvage, and any salvaged slate should stay with the building it left. Sawn slates, as against split ones, are described as possibly unacceptable on both technical and visual grounds. The thread through all of it is simple: stone that belongs to a roof is the only fair repair for that roof.

The council note identifies two rocks behind Cotswold stone slates, and both are oolitic limestones, Forest Marble and Stonesfield Slate. The first is split by hand into slates called presents; the second is split by frost, meaning the stone is left out through winter so the cold opens it along natural beds.

That is what gives a Cotswold roof its character. The rock is limestone, it opens along its own planes, and it weathers to the warm honey and grey that unify a village. Sandstone comes from a different rock family, with a different grain, a different face and a different pattern of ageing. Set beside limestone, it reads as a different material, which it is.

The note adds a point of local usage: people in the south of the district say stone tile, and in the north stone slate. Whichever word your area prefers, the rock underneath is the same limestone. Even the ridge is cut from matching material, as our answer on stone ridge tiles describes.

We can describe what shows on site without turning it into a statistic. A mismatched patch announces itself from the lane, because colour and surface differ. It can also behave differently from the slates around it. Cotswold stone is laid in diminishing courses, so every slate has a place in a graded run, graded from big at the foot of the slope to tiny at the top. A replacement that is thicker, thinner or cut to other sizes upsets the lap between courses and the line of the tails.

Weight is another reason to be careful. The council figure for a stone slate roof is about 1,000 kg to every 10 m². Approval and a structural check follow when a covering is around 15% heavier or more than its predecessor, so any substitute that changes the load calls for a word with building control before a slate is ordered.

A mixed roof also makes life harder for whoever comes next. They then have two rocks to match where there used to be one.

Matching is careful work, done before anything is ordered. We study the stone on your roof: its colour, face, thickness and the range of sizes running up the slope. A few sample slates, held against the existing courses in daylight, tell us a lot, because colour shifts once stone has weathered.

The council note adds that limestone slate from France's Côte d'Or has worked well on a number of Cotswold projects. That is still limestone, so it respects the geological rule, but it is a choice to take up with a conservation officer if the building is protected. Costs vary widely; Checkatrade's 2026 slate cost guide offers a general stone figure of about £160 to £210 per m², varying with origin, newness and location. It is not specific to the Cotswolds.

If you are weighing natural stone against manufactured substitutes, our guide to reconstituted and artificial stone slates sets out why those are a separate matter from a natural swap.

On a listed house, work that would alter the building's character needs listed building consent, and Stroud District Council says legal protection covers the whole of the building. A change of stone on a visible slope is exactly the sort of change to raise with the conservation team first. In a conservation area, ask the planning team. Planning control normally stops short of a like-for-like re-roof, since the appearance is unchanged, but check for listing and for an Article 4 direction.

When a roof is stripped, what goes beneath the stone matters nearly as much as the stone. Our answer on whether a stone roof should have underlay compares torching with modern membranes.

Photographs of your roof sent to 01453 933613, on WhatsApp or via the enquiry form give us a start. The written quote after a survey states what is included, and on older roofs stone stays stone. Our workmanship is guaranteed for 10 years, in writing. The wider subject is covered on Cotswold stone roofing.

Some roofs arrive with a patch of foreign stone already in place, laid by an earlier owner who needed a quick fix. That is not always a reason to rip it out. We photograph the patch, note its size, and judge whether it is sound, whether it sheds water, and how far it departs from the surrounding stone. A sound patch on a rear slope may simply be recorded.

A mismatch on a prominent slope, or a protected house, is another matter. There, the likely answer is to lift the foreign slates and replace them with matched limestone at the next re-lay, and to say so in the written quote, leaving the timing to you.