Daylight through the roof tiles: should you worry?

1Why some older roofs show light and stay dry

Many older houses were tiled straight onto the battens (small timber laths nailed across the rafters), with no underlay beneath them. Underlay is the felt or membrane that modern roofs carry as a second line of defence. Without it, the tiles do all the work. Each course overlaps the one below, rain runs down the surface and drops into the gutter, and the narrow slits between tile edges let a little daylight into the loft.

Some of these roofs were also finished from inside with torching, a layer of lime mortar and animal hair pressed into the joints under the tiles. Torching dries, cracks and drops out over the decades, and every patch that falls away lets in another pinprick. A loft like that can look full of tiny stars on a bright day and still keep out ordinary rain.

Fine spray or powdery snow driven by a gale can blow through the same slits and settle on the loft floor.

2Telling pinpricks from a real gap

Go into the loft in daytime, switch off the lamp and give your eyes a few minutes to adjust. Step only on the joists or on boards laid across them, never on the bare ceiling between. Hairline points of light that are small, scattered and spread evenly along the tile courses are the usual sign of an older roof that is behaving as built.

Look harder at anything that does not fit that pattern:

• a bright patch the size of a coin or larger
• a shaft of light that shifts across the loft as the sun moves
• light near a chimney, a party wall or a ridge
• damp timber, stained insulation or a drip mark below the light
• a pale tile sitting lower than the rest when you look from the garden

Photograph the same spot every month to see whether a patch of light is growing. Keep off the roof itself. A shard of broken tile lying in a gutter, or on a path below the eaves, is another clue worth noting before anyone climbs a ladder.

3What a slipped, cracked or missing tile does

A plain or interlocking tile hangs on a small nib that rests over the batten, and may also be held by a nail or clip. When the nib snaps, the nail corrodes or the batten softens, the tile creeps down the slope and leaves a gap above it. Through that gap rain lands on the underlay, if there is one, or straight onto the batten and the rafter beside it.

Wind makes it worse. Marley points out that on pitches below 30° the slope facing the wind can see strong suction, enough to rock a tile that is already loose. Wienerberger's advice is that a single-lap tile should have a mechanical fixing of its own, not just its weight. On a coast that takes gales off the Channel, a tile held by gravity alone is waiting to be lost.

The repair is small when caught early: refix or replace the tile, match its size and colour, and check the batten behind it. Left alone, one gap becomes several as neighbours lose their support, and the batten rots.

4Gaps that help the roof breathe

Not every gap is a defect. A roof void needs air moving through it, or warm damp air from the house turns to water on the chilly underside of the tiles. Older roofs ventilated themselves through exactly the gaps that let in the light. Marley's guidance, drawn from BS 5250, describes continuous eaves ventilation of 10 mm for pitches over 15° with an HR underlay, so a gap at the eaves is sometimes part of the design.

That is why filling every pinprick with expanding foam or sealant is a poor idea. You can trap moisture in the timbers, and the product does nothing about the tile that has actually moved. Our page on roof sealant repairs explains where sealant belongs and where it only hides a problem.

If you want a roof laid with modern underlay, that is a re-lay of the covering rather than a repair, and whether it is worthwhile turns on how sound the tiles, laths and rafters are. A survey sorts out which route applies.

5When to call someone, and who pays if you rent

Call for a survey if the light is bright, new, or sits near a wall, chimney or valley. A gap beside masonry often means a lifted flashing rather than a tile, and leaks where a roof meets a wall explains how that is traced. If drips follow only the worst downpours, that is a different pattern, covered elsewhere on this site.

Our visit begins under the rafters and ends on the slope, so the light you saw can be matched to the exact tile outside. You receive pictures of that tile and a written quote. Where rain is already getting in, we deal with that first. If the gap turns out to be one tile and a clip, the job stays that small.

Tenants should tell the landlord in writing, because the tiles belong to the building and not to the occupier. Landlords can read about their side on landlord roof repairs. For repairs in general, start at roof repairs.