Can a Few Missing Roof Tiles Cause a Serious Leak?

What Is Actually Underneath

When a tile goes, what is exposed is the underlay: a membrane laid across the rafters under the battens, whose job is to catch the small amount of water that blows past a covering and drain it into the gutter.

It is designed to do that in the dark, protected from sunlight and from direct weather, for the life of the roof. It is not designed to be a roof covering, and exposed to daylight and wind it does not last.

Older roofs have bitumen felt, which goes brittle and cracks. Newer ones have a breathable membrane, which is tougher but is degraded by ultraviolet light and tears once it starts to flap. Either way, a hole in the covering means the second barrier is now the only barrier, and it is on borrowed time.

So Will It Leak?

Often not immediately, and that is exactly why missing tiles get ignored. The felt sheds the water, nothing shows on the ceiling, and the gap becomes part of the view.

What happens next depends on which way the gap faces and how exposed the roof is. On a sheltered slope, a single missing tile over intact felt might do nothing for a year. On an exposed gable, wind drives rain straight at the gap, the felt flexes and tears at the batten line, and you have water inside within a couple of wet weeks.

The other thing that happens is wind. A tiled roof works partly because the tiles hold each other down. Take one out and its neighbours have a free edge for the wind to lift, so the second and third tiles go far more easily than the first one did. That is why a single gap in autumn is often three gaps by February.

What It Costs to Leave It

The sequence, when it runs all the way, goes like this. Tile goes. Felt exposed. Felt fails over that area. Water reaches the battens and the rafter tops. Timber stays damp through a winter. Battens soften; nails hold less well; the tiles around the gap start to slip because what they are nailed into has gone spongy.

At that point the job is no longer replacing a tile. It is stripping back an area, renewing battens and underlay, and relaying the covering — and if the rafter tops have gone, more than that.

Nobody needs to panic about one tile. But the gap between "replace a tile" and "strip and re-batten a section" is a large one, and the thing that moves you from the first to the second is time.

Slates Behave Slightly Differently

On a slate roof a slipped slate usually leaves a narrower gap than a missing tile does, but slate roofs are frequently older and their underlay — if there is any at all — is correspondingly more fragile. Plenty of Victorian roofs have no underlay whatsoever, or have torn bitumen felt with nothing much left in it.

On those, a missing slate is a hole straight into the roof space. It is worth treating with more urgency, not less, precisely because the building is older.

If a Tile Has Come Off

Take a photo from the ground, and look along the whole roof rather than at the obvious gap — slipped tiles that have not yet fallen are easy to spot from the pavement once you are looking for a line that is not straight.

Do not go up. Do not lean a ladder against the gutter. And do not put the tile back yourself if you have found it in the garden, because getting a tile back into a course means lifting the ones above it and they are not designed to be lifted by hand from a ladder.

Then get it dealt with while it is still a tile. That is the entire message of this page.