The short answer
Daylight through the roof from the loft means there is a gap somewhere in the covering. On a roof laid without underlay, a few pinpricks of light between tiles are common and often harmless. On a roof with felt or modern underlay, visible daylight points to a tear, a missing tile or a gap that lets rain through, and needs checking.
What daylight in the loft actually shows
When you stand in a loft with the light off and see bright lines or dots, you are seeing straight through the roof. Light can only reach you through a gap, and where light goes, wind and rain can follow. What you need to know is how much of the weather protection relies on that particular gap being shut.
That depends on the roof's make-up. Older houses were often roofed with tiles or slates laid straight onto battens, with nothing underneath them. Later roofs have a layer of underlay, a sheet of felt or breathable membrane that catches the rain that gets past the tiles. The same chink of light means very different things on each, which is why a roofer wants to know the construction before offering an opinion.
Older roofs with no felt
On a Victorian or Edwardian terrace you may see daylight in several places and never have had a leak. Plain clay tiles and slates lie in overlapping courses, and the overlap, not a membrane, keeps the rain out. Some of the pinpricks are small gaps between tiles that fill with water vapour and dust and cause no harm. These roofs also breathe, which helps stop the timbers rotting.
What matters is the size and position. A chink beside a hip or ridge may let wind-driven rain in. A gap where a tile has slipped is a different matter from the ordinary small spaces between tiles. Fine powdery snow can blow through such gaps in winter and settle on the ceiling insulation, melting later. A cluster of bright spots in one place suggests slipped or broken tiles rather than normal ventilation.
Roofs with felt or modern underlay
If you can see daylight through a roof that has underlay, the underlay has been torn, has slipped or was never lapped properly. Felt on older roofs can crack and rot with age, and it can be nibbled by rodents. Light seen along the line of a batten often means the felt is torn there. Light near a chimney, in a valley or beside a wall suggests a flashing or soaker has pulled away.
Underlay is the backup that stops wind-blown rain and small leaks from wetting the loft. Where it is gone, tiles carry all the load alone. A roof like that may seem fine in light rain and let go in a storm. Look at the felt for sagging, tears and wet patches near the light. Our page on blocked roof valleys describes one spot where water leaves the intended path and finds the gap.
How to look properly
Pick a bright day, close the hatch behind you and let your eyes adjust for a couple of minutes. A loft that seems black at first often turns out to be speckled with light. Move slowly along the loft with a torch switched off and note where light shows, then switch on the torch and check the same spot for damp timber, stained felt or mould. Mark the area with a piece of tape or take a photograph so a roofer can find it from outside, and note which direction the slope faces, since a gap on the weather side matters more than one on the sheltered side.
Do not push at the tiles from underneath. Pushing a tile can crack it, and old plain tiles can slide. Do not stuff insulation or foam into gaps either. That blocks ventilation and hides the fault. The Energy Saving Trust (guidance updated May 2026) advises against using sprayed foam beneath a leaking roof in place of a proper repair above it. Shutting a gap from inside is no cure while the cause outside remains.
When it is worth a survey
Book a look if the light appears in a patch rather than as scattered dots, if it lines up with a stain, if the light sits near a hip, ridge or flashing, or if you can feel a draught as well as see light. A survey is also sensible after a storm, when tiles may have lifted without being obvious from the ground, and before you lay new insulation or board out the loft, because covering the evidence makes later diagnosis much harder.
Many fixes are small. Refixing or replacing a few tiles, patching a torn felt section from outside or fitting a new flashing can restore the cover. If the roof has widespread slipped slates or rotten felt, patching has limits and the conversation turns to recovering. Our page on sagging roofs covers cases where the structure itself moves, and small leaks that seem able to wait deals with the timing question.
What we check from outside and in
We walk the loft first, noting every spot of light, then look at the roof from outside to match each one with a tile, slate, hip or flashing. The written quote includes pictures of your roof, and it proposes the least work that closes the gap properly. Some jobs fit under fixing a leak from inside as a temporary step, but real repair is done from the outside.
This sort of work belongs to our roof repairs service and carries a 10-year workmanship guarantee in writing. Spotting the light early, before a winter storm, is usually cheaper than waiting for the ceiling to tell you.