What are stone ridge tiles and how do they differ from clay?

The ridge is the highest line of the building, the crest where the two slopes come together. Its job is to cover the join so that rain cannot get in at the highest point. On most modern roofs that job is done by a manufactured ridge tile in clay or concrete, bought by the box and all the same shape.

A traditional stone roof does it differently. Cotswold District Council's technical guidance records that, from the beginning, a ridge was a dressed block worked to a simple angle. In everyday terms, a mason takes a block of the right limestone and works it into an upside-down V that sits astride the apex. No mouldings, no rolled top, no decoration. The plainness is the point.

Because each piece is cut by hand, every one differs slightly, and the run along a roof looks irregular in a way that suits the slates beneath. That irregularity is part of why a stone ridge is so hard to imitate with a factory product.

The ridge is the most visible line on the roof. From the road it is the edge against the sky, and a mismatched ridge shows instantly. English Heritage policy, as set out in the council's guide, keeps sandstone and limestone slates apart on any building, and the same thinking applies to the ridge. A limestone roof should be capped in limestone. Our page on sandstone and limestone explains why the two do not mix.

Weight is the second reason. Stone is heavy, and stone ridge sections are among the heaviest single pieces on the building. The slope and the ridge board are built to carry them, and a lighter covering sits differently.

If you are comparing a stone roof with a Welsh slate one, the ridge is one of the clearest differences. We look at the full comparison on stone against Welsh slate.

A stone ridge sits at the apex on a bed that holds it level and seals the joint beneath. In a traditional job that bed was lime-based, and our page on lime torching covers the related practice inside the roof.

Over decades the bedding weathers. Frost gets into the joints, the lime softens, and the stone starts to shift. Heavy pieces can slide a little along the ridge, leave gaps at the joints and let rain into the roof space. A ridge that has begun to open is usually visible from the ground as a ragged line or a slight tilt.

For modern tiled roofs the position is different. Under BS 5534:2014, bedding mortar on its own no longer carries the load for ridge and hip tiles, so a mechanical fixing goes in too. That standard is written around manufactured tiles, so a stone ridge is a case where we agree the method for the specific building before work starts.

You can check a ridge from the garden or the road on a clear day. Look at the line against the sky. It should be steady, with no dips or sudden steps. Gaps at the joints between stones, vegetation growing along the top and stones that sit at an angle all point to bedding that has failed.

Inside the loft, look at the underside of the apex after rain. Daylight, damp timber or a stain on the ridge board suggests water is entering at the top. Because the ridge is the highest point it takes the most wind, so even a modest fault can get worse quickly in a storm.

Do not climb up to test it. A loose ridge stone is heavy enough to cause real harm if it falls, and the slates around it are easily cracked by a foot.

If the stones are intact and it is just the bedding that has let go, the ridge can often be lifted, cleaned and reset. Each piece goes back in its own place, so the roof keeps the same line. Where stones have cracked or been lost, replacements have to be dressed to suit, in the matching stone.

If the ridge has been stolen, the replacement is a matter of finding and cutting stone, and the steps are on our page about stolen stone slates. For what lies under the slates, including the underlay, see underlay for stone roofs.

Ask any contractor what is proposed for the new bed, how the stones will be held, and whether the old stones are being reused. A quote that simply says "ridge tiles" without saying what they are made from is a warning sign.

A couple of photographs of the ridge from the ground, taken from two or three positions, are enough to start. Add one from the loft if you can reach the apex safely. We will say whether the fault is the bedding, the stones or something below them.

Our survey ends with a written quote and pictures from your own roof, and the work we recommend is the lightest that cures the fault, whether that is resetting a few stones or rebuilding a length. A ridge can usually be done without disturbing the main field of slates, though the survey shows whether the battens beneath are sound. See our Cotswold stone roofing page for the wider picture.