Slipped tile or cracked slate — what's actually wrong

“Slipped tile” and “cracked slate” get used as catch-all terms for any roof damage involving tiles or slates. They’re actually two quite different problems with different causes, different urgency, and different fixes.

What’s a slipped tile?

A slipped tile is one that’s moved out of position. Usually you can see it — there’s a gap in the roofline, a tile lower than its neighbours, or a tile sitting at the bottom of the roof slope where it shouldn’t be.

The most common causes:

• Failure of the nail or fixing — every tile is held by at least one nail or clip. Old nails (especially on Victorian terraces) corrode and eventually let go. The tile doesn’t fall off — it slides down the roof until something stops it.
• Movement of the batten — the wooden batten the tile hooks onto can warp or rot. The tile can still be intact, but its support has gone.
• Wind damage — high winds can lift tiles that were marginally fixed. Sometimes the tile comes off entirely, sometimes it just shifts.
• Foot traffic — anyone walking on a tile roof who shouldn’t be (including over-confident roofers and over-curious homeowners) can dislodge tiles.

A slipped tile is rarely urgent in the moment, but it can let water in through the gap it leaves. The felt underneath usually catches the water for a while, but it’s not designed as a long-term waterproof layer.

What’s a cracked slate?

A cracked slate is exactly what it sounds like: a slate that’s split. Natural slate is brittle. It can crack from:

• Impact — a branch falling, a slipped tile from higher up hitting it, foot traffic on the roof.
• Frost damage — water gets into small pores in the slate, freezes, expands, and the slate cracks. Common after a hard winter on older slate roofs.
• Age — old Welsh slate, particularly from the Victorian quarries, gets brittle with age. We’ve replaced 80-year-old slates that have simply crumbled when touched.
• “Delamination” — some imported slates (particularly cheap Chinese slate from the 1990s and 2000s) delaminate in layers rather than crack cleanly. They look fine on top and fall apart underneath. A known industry problem; if you’ve got a 15-25 year old roof and the slates are mysteriously failing, this is often why.

A cracked slate usually stays in place for a while because of the overlap from the slates above and below. But the crack lets water through, and over time the crack gets worse.

How to tell from the ground

• Tile displaced, still on the roof — slipped tile.
• Tile missing from the roof, found on the ground or in the gutter — slipped or blown-off tile.
• Tile visible but cracked — usually visible as a darker line across the tile.
• Slate with a hairline crack, often diagonal — cracked slate.
• Bits of slate in the gutter — flakey, layered debris means delamination.

How urgent is each?

Slipped tile, gap visible: not urgent in dry weather, but worth fixing within a few weeks before the next rain. A single missing tile can let in a lot of water in a storm.

Cracked slate, no displacement: less urgent than a slipped tile, but the crack will grow. Worth fixing within a few months.

Multiple slipped tiles or widespread cracking: more urgent. The felt underneath is doing the work it wasn’t designed for. The longer this goes on, the more expensive the eventual repair.

Slates crumbling when touched or delaminating in layers: the slate itself has failed. If it’s a known batch problem, the whole roof may need re-slating.

What the fix usually looks like

• Slipped tile: lift the surrounding tiles, hook the displaced one back onto a new fixing (or replace the nail), put it back in place. Quick job.
• Cracked slate: usually replaced. Lifting the slates above and “nibbling” out the broken one with a slate ripper, sliding a new slate in, fixing it with a copper nail. Standard technique.
• Multiple failures: we usually recommend a partial strip and re-slate rather than individual replacements — quicker, cheaper per slate, and gives us a chance to check the battens and felt underneath.

If you’ve spotted something and you’re not sure what it is, send us a photo and we’ll tell you what we’re looking at before coming out.