The short answer
Matching stone roof tiles come from reclaimed stock salvaged from other roofs, from new stone cut at a quarry, or from reconstituted copies. Reclaimed tiles usually match best on an old roof because the colour, thickness and weathering already agree. A roofer who knows stone will source by size and thickness, not just colour, and will tell you which route suits a listed or conservation area house.
What matching actually means with stone
Colour is the first thing people notice, but it is the least reliable test. Stone tiles on an old roof carry lichen, staining and long exposure to weather, so a new tile looks bright beside them for a long time. A good match depends on four things in order: size, thickness, the type of stone and only then colour.
Size matters because the courses shrink up the slope, with the biggest tiles at the bottom edge and the smallest near the top. A repair needs tiles that fit the course they go into. Thickness matters because a thin tile beside a thick one leaves a visible step and can let water in at the lap. The stone itself matters because limestones weather and hold moisture differently. A tile of the wrong stone may flake in frost long before its neighbours.
This is why a catalogue photograph cannot tell you much. Matching is done on the roof, with sample tiles held against the existing courses.
It also helps to know where the roof is seen from. A front slope facing the street deserves the closest match, while a rear slope hidden behind a parapet or an extension can take a slightly different tile without anyone noticing. Deciding which slope gets the best stone is a sensible way to stretch a limited supply of reclaimed tiles across a whole repair.
Reclaimed stone tiles
Reclaimed stock is the usual first choice for repairs. The tiles have already weathered, so they sit in a roof without announcing themselves, and they come from the same family of stone as the ones you are patching. Salvage yards, demolition sites and other re-roofing jobs are the sources.
There are catches. Stock is mixed, so you may get a sound pile in one size and little in another. Tiles must be graded for cracks, delamination and soft edges before they are used. Old nail holes and peg holes can leave a tile weak at the head. A roofer sorting reclaimed stone discards a fair part of any batch, and the price reflects that sorting.
Your own roof is also a source. When part of a roof is stripped, the best tiles from the least visible slope can be moved to the elevation the street sees, and the damaged ones replaced with salvage on the back. Slate roofs are re-fixed with the same care, and our answer on slate nails explains what holds the tiles on afterwards.
New natural stone
New stone is cut at a quarry and sold in sizes to suit the roof. It is the right route when a large area needs recovering and reclaimed stock is not deep enough. Lead times can be long, and the new tiles will look pale and fresh against old ones for some years before they weather in.
It is also heavier than slate. Check that the structure is fit to carry it. Planning Portal says that a new covering which makes the roof covering 15 per cent heavier or more needs building control approval, so a change from slate to stone should be raised at the start.
Cost is dealt with in the answer on what stone tiles cost. New stone is dearer than slate and usually dearer than reconstituted stone.
Reconstituted copies, and when they are not enough
Reconstituted stone slates are cast from stone aggregate and a binder to imitate the real thing. They are consistent in size, easier to buy and lighter on the budget. Bradstone's Cotswold range, for one, lists a minimum pitch of 30 degrees and a laid weight of about 84 kg per square metre, so the figures are available before you commit.
They are a sound choice on a new build or an extension where an exact match to an old roof is not needed. They are a poor choice where real stone is part of the building's character. A council appraisal of one village near Bath warns that concrete re-covering "detracts markedly" from the stone roofs around it, and a cast tile sits closer to that than to real stone.
If your house is listed, replacing real stone with an imitation will need listed building consent from B&NES Council, and a conservation officer may well refuse it. Speak to the council first, before any tiles are ordered.
How we approach a stone roof
We start with the survey. On a stone roof that means looking at the courses, the thickness, the pegs or nails, and what is under the tiles, then deciding whether the right answer is a patch repair, a partial re-lay or a full re-roof. Repair comes first wherever it works.
Where tiles need replacing we source by size and thickness, show you the samples against your own roof, and tell you which route we recommend. If the work is notifiable, we handle the Building Regulations side. If you have any spare stone tiles in a garage or garden, keep them aside for the survey, since they show the original source and thickness better than a photograph can.
If the roof is an older slated or stone-tiled terrace, our note on Victorian slate roofs covers how the same matching principles apply to slate, and the slate roofing service page sets out our wider approach.
