The short answer
Broken tile nibs are the small lugs on the underside of a roof tile that hook over the batten. When a lug snaps, the tile hangs only on its fixing and gravity wins, so it creeps down the slope or drops out. One or two can be swapped for sound tiles. If lugs are failing across a whole slope, the tiles are tiring together and a re-roof is the sensible conversation.
What a nib does, how old concrete tiles lose them, how you can spot the problem from the garden, and what tips a repair over into a re-roof.
What a nib does and why it breaks
Turn an interlocking concrete tile over and you will find one or two small projections near the top edge. Those are the nibs. Each one catches on a batten, the thin timber strip fixed across the rafters, and together they carry much of the tile's grip on the roof. A nail or clip resists wind lift, but the nib does the everyday work of resisting the slide downhill.
Nibs are slim and cast from the same concrete as the body of the tile, so they age along with it. Frost opens hairline cracks, damp lingers where nib meets batten, and after many winters a lug can shear off cleanly. Marley's figure for how long a concrete tile lasts is around 60 years, offered without any guarantee, which puts a roof from the 1950s or 1960s squarely in the age band where this starts to happen. Rough handling during earlier work can also snap a lug, and the tile then sits quietly for years before it moves.
The tile rarely falls at once. A broken nib tends to show as a tile that has slumped a little below its neighbours, held by a single nail, until a gale completes the job.
Spotting nib failure from the ground and the loft
Walk round the house and study each slope slowly, ideally when low sun throws shadows across the surface. Sound tiles sit in dead-straight rows. A tile with a snapped nib rides a touch lower than the course around it, shows a thin dark gap at its head, or has already vanished and left the batten exposed. Binoculars help, and so does zooming in with a phone camera. Keep your feet on the ground while you do it.
Check the gutters and any flat roof below as well. Small triangles of concrete in the gutter, or chips on the path by the downpipe, suggest tiles are shedding edges and lugs. From inside, a torch in the loft sometimes finds pale crumbs on the underlay or the insulation under a failing patch, and a chink of daylight at a tile's head deserves a mention to the roofer.
Notice where the slipped tiles are. A few near the eaves or around a chimney can come from one disturbed spot. Tiles creeping in scattered places across the whole slope point towards age. Our answer on why roof tiles slip covers the look-alike causes, such as soft battens and rusted nails.
One tile, one patch or the whole slope
The deciding question is how many nibs have gone and where they are. With one or two failed tiles and sound battens beneath, the repair is straightforward: lift the tiles above, slide the damaged one out, hook in a sound match and fix it down with a clip or nail. The method is set out in our answer on replacing individual roof tiles.
The picture changes when lugs keep snapping as tiles are lifted. Tiles that crack in the hand tell the roofer how brittle the batch has become, and each repair then disturbs the next weak tile. Swapping in tiles taken from the same slope only moves the problem around. If every tile is the same age and in the same state, a patch buys a short reprieve.
That is the point at which we talk through stripping the slope and covering it afresh. Your survey photos show the tiles we lifted, the nibs we found and the battens below them, so the recommendation rests on evidence you can look at, and the quote gives one total for the whole job.
Costs and what to ask the roofer
For a national yardstick, Checkatrade's October 2026 tile replacement table gives £170 to £500 for five tiles, with the upper figure applying where scaffold is needed. Its June 2026 repair table puts concrete tile repairs at £90 to £120 per m², with VAT extra, for areas of up to 3 m². Treat both as general guides rather than a quote for your house, and ask each roofer whether VAT and scaffold sit inside their total.
A few questions are worth putting to anyone who looks at the roof. How many tiles had broken nibs, and are they clustered or scattered? What state are the battens in? Will the new tiles match the profile and be clipped or nailed? And if a re-roof is recommended, can the roofer show you the evidence on your own roof?
Our pitched roofing page sets out repairs and re-roofs in more detail. If you want us to look, tell us which slope the slipped tiles are on and attach a few ground-level snaps of it. We check the pattern of failure before anything else, because that pattern decides which job you have.
More on this in Pitched Roofing Services in Crawley
Two more nib questions
Can sealant or mortar hold a tile that has lost a nib?
Not for long. A dab of sealant or mortar bonds to a surface that is already weathered and moves with every frost and heatwave, so the tile slips again, often taking its neighbours with it. The lasting fix is a replacement tile that hooks properly over the batten and is clipped or nailed in place.
Do all slipped tiles have broken nibs?
No. Tiles also slip when the batten has rotted, when nails have rusted through, or when an old repair was never fixed down. Turning a removed tile over shows which it is. Photos of the underside, taken during the survey, tell you whether the tile or what it hangs on is the real fault.