The short answer
There is no fixed figure, because ridge mortar fails from the weather and the movement of the roof, not from age alone. A well-laid bed on a sheltered roof can last for many years. On an exposed roof, or one with a weak mix, it can start cracking much sooner. What matters is checking it. Cracks, missing pointing, loose tiles and green growth along the joints show the mortar is breaking down, and it is cheaper to act then than after a tile has fallen.
What ridge mortar does
On a traditional roof, the ridge tiles sit on a bed of mortar laid along the top of the roof where two slopes meet. The mortar levels the tiles, fills the gaps and, in older roofs, is the main thing holding them in place. It is also a sealant, keeping wind-driven rain out of the roof space. Because the ridge is the highest and most exposed line, the mortar takes more weather than any other joint on the house.
Why it breaks down
Mortar is hard and rigid, but roofs are not. Timber expands and shrinks with moisture and temperature, and a house settles and shifts. A rigid bed cannot follow that movement, so it cracks. Water then gets into the crack, freezes in winter and expands, and pushes the crack wider. Over the years the surface turns sandy, the pointing falls out in lumps and the bed becomes hollow behind the tile. A mix that was too strong can crack sooner than a softer one, and a mix that was too weak can crumble and wash out.
Workmanship matters. Mortar laid on a wet or dirty surface, or in cold weather, bonds poorly. Tiles pressed into too thin a bed leave voids. Our guide to ridge bedding mortar, mixes and colour matching explains how a good bed is made.
Exposure and orientation
The side of the house facing the prevailing south-westerly weather in this part of Hampshire takes the most rain, and a roof on open ground near the edge of an estate gets stronger wind than one sheltered by neighbours. Frost cycles in winter do the most damage, since the roof gets wet, freezes and thaws repeatedly. A north-facing slope stays damp for longer and grows moss along the ridge, which holds moisture against the joints.
Signs the mortar is on its way out
From the ground, look for pale or dark lines where pointing has fallen out, lumps of mortar in the gutter or on the path, tiles sitting out of line, and moss or lichen along the joints. In the loft, daylight at the ridge or damp staining shows water getting in. If a tile moves under a gloved hand or sounds hollow when tapped, the bed beneath has failed. Our page on the signs your ridge tiles are failing goes through them in order of urgency.
Repointing or re-bedding
If the joints are cracked but the bed below is still firm, repointing may be enough. If the bed has crumbled or the tiles rock, the ridge needs lifting and re-bedding, with the tiles refixed on fresh mortar. Under BS 5534:2014 the tiles should also be mechanically fixed, so a re-bed is a good time to add that. The choice between the two is set out in our comparison of re-pointing and re-bedding ridge tiles.
Keeping a mortar ridge going longer
Small habits help. Keep moss off the ridge line, because it holds water against the joints. Have the roof checked after a severe winter, when frost damage shows. Repoint early, while only the surface has gone, since pointing a firm bed costs far less than rebuilding a hollow one. Ask for a mortar that is compatible with the tile, not simply the hardest mix available, and for added mechanical fixing so that the tiles are not relying on the bond alone. A bed that is allowed to break down completely takes the tiles with it, and a slipped ridge tile can drop onto a path or a car.
Moving to dry ridge
If you have had repeated repairs to a mortar ridge, a dry ridge removes the part that keeps failing. It replaces the bed with a batten, clips and screws. Our answer on how long a dry ridge lasts covers that side of the question, and the guide to dry ridge against mortar compares them.
What a repair costs against a rebuild
A repoint is a short job on a ridge that is otherwise sound, while a full re-bed means lifting every tile, cleaning the bed away and laying the ridge again, so the bill rises with the length of the ridge and the access needed. Our guide to ridge tile repair and re-bedding costs gives the typical ranges, and the survey gives your own figure.
What we do
We survey the ridge, photograph the cracks and the bed, and tell you which repair is justified. If a tidy repoint will do, we say so. The fixed written quote lists what is done. For the full range of ridge work, see the Basingstoke ridge and verge work page.
Every roof is different. A free survey with photos settles it for yours.
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