A stone-tiled roof is built differently from any other covering on a Bath house. The tiles are thick, uneven slabs of limestone. They are laid in courses that shrink from heavy tiles at the eaves to small ones near the ridge, each tile is hung on a timber peg, and the gaps underneath are sealed with lime. Repair therefore means working with that system, not substituting for it. Replace a few tiles with the wrong size and the courses no longer line up. Fill a gap with cement and you can trap water in the stone. This guide explains the parts of the roof, the faults we find on them and the way each is mended, from re-hanging slipped tiles to re-torching the underside. It also covers when a patch is enough and when a section needs relaying, and what permission an old stone roof may need before work begins.
How a stone-tiled roof is put together
Stone tiles are cut or split from limestone, so they are far thicker and heavier than slate and rougher on the face. Each one is a different size. A roofer who lays them sorts them first, grading the tiles by length and width, and then lays the largest at the eaves, where the roof carries most water and most weight, and the smallest at the top. The courses between step down gradually. These are the diminishing courses, and they give a stone roof its soft, graded look from the ground.
The tiles are not nailed in the way slate is. A hole near the head of each tile takes a peg, traditionally made from oak, which hooks over a timber lath or batten. Battens are the narrow timber strips fixed across the rafters, and on an old roof they may be split oak laths rather than sawn softwood. The tile hangs from its peg and rests on the course below, and its weight and the overlap hold it against the wind.
Underneath, the roofer fills the joints with torching, which is lime mortar pressed into the underside of the tiles from the loft side. Torching stops wind-blown rain and fine snow from being driven up between the tiles, and it also helps to hold the tiles from rattling. On many old roofs there is no underlay at all, and the torching does that job.
The rest of the roof follows the same logic. Hips and valleys on stone roofs are often formed with tiles cut to the shape of the angle, or lined with lead where the slope runs into a wall. Ridges are usually capped with stone or clay pieces bedded on lime. The weight of all this on the roof frame is considerable, and the timbers have to be sound to carry it.
Because each of these parts depends on the others, trouble in one place tends to travel to the next. A rotted peg lets a tile slip, a slipped tile lets water onto the torching, and washed-out torching lets the next tile loosen.
What goes wrong on an old stone roof
Stone roofs last a long time, but they age in particular ways, and the signs are specific enough to spot with binoculars from the garden or with a torch from the loft hatch.
Peg failure
Oak pegs rot, split or shrink in their holes over time. When a peg lets go, the tile sinks and comes to rest on the tile beneath. That leaves it sitting low and out of line, or it falls and breaks. A run of slipped tiles across one slope usually means the pegs and laths are tired, not that the stone has failed.
Stone decay
Limestone tiles can flake and split with frost and moisture. Where a tile has begun to delaminate, the face peels away in layers and the tile loses thickness. A lightly flaking tile may survive for years, but one that has gone soft and crumbly will not shed water properly and should be replaced.
Torching loss
Old torching dries, cracks and falls away. You may find lumps of lime in the loft, or daylight where the roof should be dark. Without it, wind-driven rain reaches the battens and the timbers beneath, and a roof that looks sound can be rotting inside.
Moss and damp
A stone roof holds moisture and grows moss readily, especially on shaded slopes. Moss does limited harm in a thin film, yet a deep cushion keeps the stone wet and clogs the laps. Cleaning must be gentle, and pressure washing a soft stone tile can strip its face.
Cement and wrong repairs
The most damaging faults are often earlier repairs. Cement mortar used for pointing or bedding is harder than the stone and does not let it breathe, so water gets trapped and the stone around it decays. In its comments on a listed house in Walcot, the Trust argued for lime and named cement as a probable cause of damage to the stone.
Sorting, re-hanging and relaying the courses
Repair starts with a simple question: how many tiles are sound enough to go back? On a stone roof the answer matters, because the original tiles are the best match you will ever get, and new stone of the right size and colour is hard to source. We lift the roof section by section, take the tiles down carefully, and sort them on site by size and condition. Sound tiles are stacked in their size groups, damaged ones are set aside, and the roof is rebuilt with the sorted stock in the right order.
Where the fault is local, the repair is local too. A few slipped tiles can be re-hung on new oak pegs, and a cracked one replaced from stock of the same size and weathering. We keep that stock from earlier jobs when a roof has to be stripped, because a new tile laid among weathered ones stands out for years. Our guide to matching stone tiles explains how we choose between reclaimed and new.
When pegs and laths are tired right across a slope, the sensible repair is to strip that slope and relay it. The courses are set out again from the eaves with the sorted tiles, new battens or laths are fixed, and each tile is pegged. The skill lies in keeping the diminishing order, so the largest tiles go back at the bottom and the sizes step down evenly. A roof relaid in random order loses the graded look and sheds water less well, because the laps no longer suit the tile sizes.
Nothing about this is quick. A stone roof takes longer to lift and relay than a slate or tile roof of the same area, because every tile is handled, graded and placed by hand. That time is a main reason the work costs more. We look at what drives the figure on our page about stone tile cost.
Weight is the final point in this part of the job. A stone roof is heavy, so the rafters and wall plates need to be sound before the load goes back on. If we find rot while the roof is open, we tell you and price the timber repair, because covering a weak frame again with stone only stores up the problem.
Pegs, laths and torching: the hidden repairs
The parts nobody sees from the street are the parts that decide how long a repaired roof will last. Pegs, laths and torching all fall in this group, and a good repair renews each of them where it has failed.
New pegs are cut from oak, as the originals were, and sized to suit the hole in each tile. A peg that is too slack lets the tile rattle and shift, and one that is forced in can split the stone. Where a tile has lost its hole to wear, it can be re-drilled, though a tile with a cracked head is better replaced. Some modern repairs use stainless or copper fixings in place of pegs, which hold well but do not match the original, so the choice depends on the roof and on whether the building is listed.
Laths and battens are renewed when they are rotten, split or too weak to carry the tiles. Replacing them is a good time to check the rafters, because a roof stripped to the frame lets us see what the timber is doing. Where the sort of lath matters for the look or for the listing, we match it.
Torching is the repair most often missed. When we relay a section, the underside is torched afresh with lime mortar, pressed in from the loft so that it fills the gaps between tiles without squeezing out onto the face. Lime is used for a reason. It is softer than the stone, it lets moisture move out of the roof, and it can be repaired later without damage. Cement does none of this.
The same goes for flaunching, the mortar fillet that caps a stack and throws rain off the pots. The Bath Preservation Trust has said a lime-based mortar is the right choice for flaunching on a listed stack, and cement has been blamed for stone damage in the same case.
Ridges, hips, valleys and the lead around them
A stone roof is only as watertight as its junctions. The tiles are rough and thick, so the angles of the roof need particular care.
Ridges on stone roofs are capped with stone or clay pieces, bedded on lime. Under BS 5534:2014 the strength of mortar by itself is no longer counted on for ridge, hip and verge pieces, which means a mechanical fixing is added. On a historic ridge, that is usually done with stainless or copper fixings hidden within the bedding, so the look is unchanged. Dry-fix, a clipped ridge with no bedding, is another route, but those systems are designed around regular modern tiles and sit awkwardly on rough stone.
A valley forms along the inner angle between two slopes, and rain from both runs down that line. On some stone roofs the valley is formed in the tiles themselves, with the courses swept round the angle. On others it is lined with lead. Lead valleys fail at splits, at laps and at the drips, and when they do the water runs straight into the roof timbers. We cover the bigger picture on our lead roofing page.
Against a wall or beside a stack, each junction is closed with a flashing, which is lead worked over the junction, and soakers, small lead pieces slipped beneath each course. Both are cut and fitted to follow the irregular line of the tiles, which takes time and skill. Cover flashings are wedged into a mortar joint in the wall, and the joint is repointed in lime.
Verges, the side edges of a gabled roof, need the same care. The tiles are bedded on a mortar course, and the old bedding often fails first. We rebuild the verge in lime and fix the end tiles so that wind cannot lift them.
A ceiling stain may come from the tiles or from one of these junctions, so have the roof inspected before anything is replaced. The junction is the more likely culprit.
Matching, consent and the character of the roof
Stone tiles are part of what a building looks like, and council appraisals of villages south of Bath treat them that way. The B&NES appraisal for Wellow describes the surviving Cotswold stone tiles as rare, to be kept. The Freshford and Sharpstone appraisal adds that re-covering with concrete tiles detracts markedly from a building. That gives a clear steer for repair: keep the stone you have, match it where you must add to it, and do not swap it for a different material.
If the house is listed, B&NES Council decides whether work that alters the building may go ahead, and acting without that consent is an offence. Its advice is to make contact before any work starts, and it points out that listed building consent and planning permission do not mean the same. Even a repair meant to copy what is there can need consent when it is large. The council's listed buildings guidance gives the conservation team's contact details.
Not every stone roof is listed, but a stone roof in a conservation area still deserves care. Whether your street is covered by an Article 4 direction is something to ask B&NES planning.
Building Regulations are the other consideration. Small repairs seldom trigger them, while a large relay, or a new covering that is noticeably heavier than the old, can. Stone is already heavy, so a heavier substitute is rarely the question here, though a lighter one would change the look as well as the load. The Planning Portal and your building control body set out the thresholds. Where approval applies, we explain it and handle the Building Regulations side.
You can see how the repair fits the wider service on our slate roofing page, and how the same thinking applies to slate on our guide to Victorian slate roofs. The way each covering is held is covered in slate fixing methods.
What a specialist survey records and what you get
The survey is where a stone roof repair is decided. We go up on to the roof and, where we can, into the loft. From outside we look at the courses for slipped or sunken tiles, the state of the stone, the ridge, hips and valleys, and the flashings around chimneys and walls. From inside we look for daylight, lime on the floor, stained or rotten timbers and the condition of the laths.
Our own pictures of your slopes go into a written scope: which tiles can be re-hung, which need replacing, whether any slope needs relaying, what the torching needs and what the lead requires. Where we find timber decay, it is described and priced as its own line.
The fixed price follows in writing. Repair is our starting point, and on a sound stone roof that often means re-hanging, re-pegging and re-torching a section, not stripping the whole roof. If a full relay is the right answer, we say why, and show you the evidence.
You will find the national cost picture for slate and stone in the typical UK ranges published by MyBuilder, but those figures are not a guide to a particular stone roof. The cost depends on tile condition, access, the extent of the relay and the timber. Only a visit to the roof allows a firm figure.
Workmanship carries a written guarantee of ten years, and we leave the site clear. Should consent be in question, we explain which office to ask. To arrange a visit, call 01225 285181, use WhatsApp or complete the enquiry form.