The short answer
A hairline crack that does not run through the tile, leaves it firmly bedded and lets no water in can sometimes be monitored or sealed. A crack that splits the tile in two, lets it move, or runs along a fixing needs the tile replaced with a close match. A sealant is a short-term measure, and a roofer should look at the tile before you decide.
What kind of crack is it?
Along the crown of the roof, each ridge tile is bedded in mortar and held by fixings. A crack in one of them can be one of several things, and the differences are worth telling apart.
A fine surface crack, or craze, affects the glaze or the outer skin and does not go through the body of the tile. A through crack goes right through, and you can sometimes see light along it from the loft. A crack near the end of a tile often comes from a fixing driven in too tight, or a tile that has been stepped on. A crack that follows the line of the bedding may come from movement in the roof rather than a flaw in the tile.
Frost matters here. Water that enters a crack and freezes expands and widens it, so what is a hairline in autumn can be a split by spring. It is why we like to see cracked tiles before winter where we can.
When a cracked tile can be left
Some cracks are cosmetic. If the tile is firmly bedded and fixed, the crack is superficial or very fine, and no light or water passes through, the tile is still doing its job. In that case, the sensible course may be to leave it and note it. We would photograph it, mark where it is, and look again at the next visit. Your own photograph, taken in similar light every few months, makes any change easy to see.
That is a judgement, and it depends on the tile. Old clay ridge tiles often craze with age without losing strength. A concrete tile with a hairline crack can carry on for years. But a crack that is getting longer, or that has opened since you last looked, is telling you the tile is under strain. We will say plainly which kind of crack we think yours is, with photographs, and leave the decision to you.
If you are not sure, take a close-up photograph from a safe place, such as a bedroom window, and send it to us. Stay off the roof and shoot it from a window instead.
Sealing a crack, and its limits
A flexible sealant or a mortar fillet can close a crack and slow water entry. It is a legitimate short-term repair on a tile that is otherwise sound, and it can buy time until a larger job is booked. It does not restore strength. A sealed through crack is still a through crack, and the tile will behave as two pieces under wind and frost.
Sealants also age. They shrink, lose their grip on clay and concrete, and discolour, so a repair that looks neat in the first year may have failed by the third. On a ridge, where the tile faces the strongest wind on the roof, that is a risk we think is worth stating.
If a cracked tile can move under your hand, sealant is the wrong answer. Movement means the bedding has failed too.
When a roofer tells you a crack has been sealed, ask where, with what, and for a photograph.
When the tile has to be replaced and matched
Replace a cracked tile when the crack goes right through, the tile moves, the break runs through a fixing hole, or a section is missing. A tile that has split in two will fall in time, and our answer on what to do when a ridge tile has fallen off covers what follows if it does.
The replacement has to match: the same profile, such as half-round, angled or roll-top, and a colour that sits well with the weathered tiles beside it. A new tile among old ones can show, and where the roof faces the lane or the building is protected, we try for a closer match, including reclaimed tiles. The new tile is bedded in mortar and fixed mechanically. BS 5534:2014 also expects a screw or clip on every new ridge tile, bedded or not, so the replacement is held down twice over.
If the bedding around the cracked tile has also gone soft, we replace the tile and re-bed the short run either side, which costs little more once the access is in place.
Cost, doing it yourself, and what we do
MyBuilder's 2026 figures put a ridge tile job, re-bedded or replaced, at £300 to £600 and a minor roof repair at £100 to £300. These come from a national guide, not our price list, and access often moves the total. After the survey, the written quote covers the tile, bedding, access and waste.
Replacing one ridge tile looks simple, and people try it. The risks are working at height, standing on tiles that are not designed to be stood on, and fixing the new tile in a way that does not meet the standard. Our guide to fitting ridge tiles yourself sets out what is involved and when a professional is the safer route.
A crack at the gable end sometimes comes with a loose verge cap, and our answer on blown dry verge caps deals with that. Our 10-year workmanship guarantee is given in writing for the finished work, and the full range of ridge, hip and verge work is on our ridge, verge and dry-fix page.