Three designations overlap in Bath: World Heritage status for the city, a separate conservation area designation over a good part of it, and listings on individual buildings. Under any of them the ridge is a small part of the roof that changes a great deal about how the house reads from the pavement. A pale cement bed with grey pointing laid against a warm old clay ridge draws the eye in a way that a matched lime bed does not. It is written for anyone with a listed or conservation-area roof who needs the ridge repaired and wants to know what lime mortar is, why it gets chosen, how the ridge is matched to the original, and which conversations to have with the council beforehand. It deals with bedding in lime and matching the look. The general method of re-bedding is described elsewhere, and so are the questions of dry-fix on old roofs, which is a separate decision.
What lime mortar is, and why old roofs use it
Lime mortar is made from lime, sand and water, and it hardens slowly, drawing carbon dioxide from the air as well as losing water. Modern mortar is made with Portland cement, which sets quickly, becomes very hard and is almost waterproof. The two behave quite differently once they are on a roof.
Lime is softer and more flexible than cement. A ridge flexes slightly with temperature and with the movement of the roof, and a softer mortar takes up that movement by developing fine cracks that can close again, not by breaking away from the tile. It is also more permeable. Moisture that gets into the ridge, the masonry or the timber has a route out through the lime, where cement can trap it. And lime is weaker than the tile and the brick or stone around it, which is the point: if something has to give, it should be the mortar, which can be renewed, and not the historic fabric, which cannot.
That reasoning is why conservation bodies prefer lime on traditional buildings. When Bath Preservation Trust commented on repointing at 7 Walcot Buildings, it wanted lime used, because old stonework needs to breathe, and cautioned that cement on a listed house may have worsened the stone decay. That case concerned a chimney stack, not a ridge, but the principle is the same for any bedded detail on an old roof. It is a casework comment, not a published policy, and we cite it as an example.
Lime is slower to work with. It needs protecting from rain and frost while it cures, and it is more sensitive to the mix and the weather, which is why it is done by people who work with it regularly. It also looks different once cured: a lime ridge has a softer, slightly textured surface and a tone that sits with old tile far better than a cement finish does.
Which roofs call for lime, and which do not
The date of the house matters less than the materials on it and what the owner wants to keep. Lime is the right default on a listed building, on a conservation-area roof that still has its original ridge, and on any older house whose tiles, slates or stone slates are traditional.
On a newer roof of concrete tiles with a cement bed, it makes less sense to switch to lime simply for the name. A bed that suits the original materials is the better guide. Before suggesting anything we read what is there: the old mortar, the age of the tile and the way the ridge was laid.
Roofs around Bath differ from place to place. B&NES conservation appraisals for villages south of the city record red clay tiles in Wellow, with surviving Cotswold stone tiles described there as rare and worth preserving. The Freshford and Sharpstone appraisal says concrete tiles detract markedly from the look of a re-covered roof. Each of these roofs finishes its ridge differently, and the city has its own mix of slate and clay. Each of these roofs finishes its ridge in a different way, and the finish is part of why they look as they do.
A house that is unlisted but inside the conservation boundary may need no application for a ridge repair. The finished look still counts, and we would choose a bed that suits the original. If you are unsure, ask whether the repair will change what is visible from the road. If it will, speak to B&NES before you begin.
Matching the ridge: tile, profile and colour
Re-bedding in lime restores what was there, and matching is the harder half of the task. It begins with the tiles. A ridge tile has a profile: half-round, angled, roll-top or a decorative crested form. It also has a colour and a texture, which weathering has altered over many years. A new tile is the wrong shade at first, sits too crisply and shows against the old run beside it.
So the first approach is to reuse the existing tiles. They are lifted carefully, cleaned of the old bed without damaging the glaze or surface, and numbered if the profile varies. Cracked ones are set aside. Where replacements are unavoidable we go to salvage first, because a reclaimed tile of the same profile carries the weathering that a new one lacks. If new tiles are the only option, they are chosen for profile first and allowed to weather, and where the colour is a close call we show you samples.
The mortar is matched too. Its colour comes mainly from the sand and any pigment, and a small test patch can be made and left to dry before the full run. Too yellow, and the line reads as a stripe against grey slate. Too white, and it glares. We aim for a bed that recedes and lets the tile do the work. Texture is struck to match what the ridge had: flush, slightly recessed or lightly brushed, according to how the older work was finished.
On stone slate roofs, the ridge may be a stone ridge or a bedded clay one, and it is dealt with accordingly, with stone cut or salvaged to match. A hipped roof needs the same care along its hips, as our guide to hip tile repair describes, and the verges at the gables follow the same logic, covered in the guide to mortar verge repair.
Bedding in lime: method and fixings
The order of work follows an ordinary re-bed, with a few differences. The ridge is lifted tile by tile, the old bed is cleared, and the timber below is checked. Lime then calls for preparation: the tiles are dampened so they do not pull the water from the mortar too quickly. A lime bed that dries too quickly turns powdery and weak, so the work is done out of strong sun and wind, and the finished length is shaded or covered.
The mortar is laid, the tiles are pressed into it, and the joints are struck off. Lime sets slowly, so the work is protected for some time afterwards from rain, which can wash it out, and from frost, which can break it up before it has hardened. That is why lime ridges are planned around the weather, and a settled spell matters more than it would for a cement bed.
Fixings still apply. Under BS 5534:2014 the ridge, hips and verges all call for mechanical fixing, which means lime is never the only thing holding a tile on. On a traditional roof, that means discreet, corrosion-resistant fixings that tie the tile to the ridge timber, placed so they cannot be seen and do not harm the tile. The bed does the sealing, the fixing does the holding, and the look from the ground is untouched. Marley's guidance, which we follow here, makes the same point about bedded tiles generally.
If the question is whether a dry-fix ridge is acceptable on an old roof instead, the answer depends on the building and the consent position. Ventilated systems are a legitimate part of modern practice and can solve real problems with condensation under a roof, and we set out how they work in the guide to ventilated dry ridge. On a listed or visible conservation-area roof, the usual starting point is still a lime bed, and a change to dry-fix is discussed with the council first.
Consent, B&NES and what to ask before work
Consent for work to a listed building is granted by B&NES Council, and planning permission is a different thing altogether. Owners are asked to contact the council first, since carrying out work without the consent can lead to prosecution. Whether a like-for-like ridge repair needs consent on your particular house is the council's decision, so neither you nor we should assume the answer. You can read how it works on the B&NES listed buildings pages, and its conservation team can be phoned on Tuesdays and Thursdays.
A few streets have Article 4 directions that remove particular permitted development rights. Roofs are not among the examples B&NES lists, so we make no claim either way. Before anything beyond a repair, look up your road on the policy map B&NES publishes.
Building Regulations are a third, separate matter. A ridge repair by itself is unlikely to engage them, though a re-roof of the same house may, and Dry ridge and Building Regulations explains where fixing and ventilation come in. If a job is notifiable, we take that paperwork on.
Before work starts, it helps to have these in hand:
- Photographs of the ridge as it is now, from the ground and close up.
- The listing description, if the house is listed, which you can find through Historic England or the council.
- A written description of the repair, saying what is being kept, what is being replaced and what mortar is to be used.
- The council's answer on whether consent is needed, kept with your records.
Our survey supplies the photographs and the written description, and the specification goes on the fixed price so the council and you are reading the same thing.
After the work: how a lime ridge ages
A lime ridge changes as it cures. It starts a little lighter than it will end up, darkens as it carbonates, and takes on the slightly weathered tone of the roof around it within a season or two. That is expected, and it is why a patch test is useful.
It also needs less attention than people expect, provided it was done properly. Fine hairline cracks are not a failure: lime heals small cracks as moisture moves through it. What matters is whether pieces are loosening or tiles are shifting, and those are the signs that sound a warning. Glancing at the ridge from the street after a bad winter or a storm will catch most trouble early, and loose ridge tiles lists what to watch for.
Maintenance, when it comes, is modest: repointing a short length that has eroded, with the same mortar, so the repair blends. Repairing lime with cement at that point undoes the benefit of the original work, because the harder patch now traps moisture and pulls away from its softer neighbours. It is worth telling any future roofer what is on the ridge.
If you are weighing a lime ridge against alternatives, or have been given a quote that proposes cement on a listed roof, the survey is the place to start. We examine your tiles, your bed and your building, record what we find in pictures, and put one fixed price on paper. Lime needs a few frost-free weeks to cure, so ridge work on a lime bed is best planned between late spring and early autumn. Other ridge, hip and verge questions are answered across the repairs section.