A roof leak is traced by following the water back from where it shows indoors to where it first enters, then matching that point to a specific fault — a slipped tile, failed flashing, a blocked valley or storm damage. Most leaks are fixed with a targeted repair rather than a new roof, provided the underlying structure and the bulk of the covering are still sound.
Following the water back to where it really gets in
The spot where a stain appears on a ceiling is rarely directly below the entry point. Water runs along rafters, felt and battens before it drips, so it can travel several feet sideways and down before it becomes visible. Tracing a leak means working out that path in reverse, from the damp patch upwards and outwards to the breach in the weatherproof layer.
Inside, a roofer will usually start in the loft on a dry day, looking for daylight through the covering, water staining on the timbers, damp insulation, or rust on nails and clips. The highest point of staining on a rafter often marks the closest internal clue to the entry point. Felt that sags or has torn around a fixing tends to hold and channel water, which is why a stain can sit some distance from the actual hole.
Outside, the inspection focuses on the obvious weak points: ridges, valleys, the joins around chimneys and pipes, and any tiles that sit proud or low compared with their neighbours. Where the source is not obvious, a hose test is sometimes used — water is run over small sections of the roof in turn, lowest first, while someone watches inside for the moment it appears. This isolates the area rather than guessing across the whole roof.
Common entry points that get checked early include:
- Flashing joints around chimneys, parapets and abutments (where the roof meets a wall)
- Valleys, where two roof slopes meet and water is funnelled
- Cracked, slipped or missing tiles and slates
- Worn mortar at ridges and verges (the edges of the roof)
- Penetrations such as soil pipes, vents and rooflights
It is worth ruling out condensation before assuming a leak. Poor loft ventilation can cause moisture to form on the underside of the roof and drip in a way that mimics a leak, but it appears more evenly and is linked to cold, still weather rather than rain. A surveyor should be able to tell the difference by where and when the dampness shows.
Slipped tiles, failed flashing and blocked valleys
Most leaks are fixed with a targeted repair rather than a new roof, provided the underlying structure and the bulk of the covering are still sound.
These three faults account for a large share of everyday roof leaks, and each leaves recognisable signs. Understanding them helps when reading a quote or deciding how urgent a repair is.
Slipped tiles and slates happen when the nail or peg holding a unit corrodes or the batten beneath it decays. The tile slides down, leaving a gap and often pushing those below out of line. A single slipped tile may not leak at once, because the felt underneath can hold out for a while, but it exposes that layer to wind and weather and the problem spreads. Re-fixing or replacing the affected tiles, and checking the battens, is usually a contained job.
Failed flashing is one of the most frequent causes of persistent leaks. Flashing is the metal — usually lead — that seals the join between the roof and anything rising through or beside it, such as a chimney or a wall. Over time the mortar holding it into the brickwork cracks, the lead lifts in the wind, or old flashing splits. Because these joins sit at vulnerable angles, even a small gap lets water track straight in. Repairs range from re-pointing and re-dressing existing lead to fitting new flashing where the old material has perished.
Blocked valleys cause leaks by stopping water draining as it should. A valley carries a high volume of run-off, so when leaves, moss or debris build up, water backs up, pools and is driven under the tiles on either side. Mortar-bedded valleys can also crack, and metal-lined ones corrode at the bottom where water sits longest. Clearing the valley is the first step; if the lining itself has failed, that section is relined.
None of these necessarily points to a roof that needs replacing. The decision usually turns on how widespread the failure is. Isolated faults on an otherwise sound roof are repaired. When the same problem recurs across many tiles, the felt has broken down generally, or repairs are simply patching a roof that is past its serviceable life, replacement becomes the more sensible option. A roofer should be able to explain which category a roof falls into and why.
Storm damage and the first steps after bad weather
After a storm, the priority is to limit further water getting in, then to assess the damage safely — without going onto a wet or wind-exposed roof. High winds lift and dislodge tiles, tear flashing, and can drive rain under coverings that are normally watertight, while falling branches cause impact damage. The full extent is often not visible from the ground.
The sensible order of actions is straightforward. First, contain any water indoors: move belongings, place containers under drips, and if water is pooling above a ceiling, a small hole made deliberately can let it drain in a controlled way rather than collapsing a larger area. Second, look at the roof from the ground or an upstairs window for missing or shifted tiles, displaced flashing and debris. Third, arrange a proper inspection once conditions are safe.
Temporary measures, such as a weighted tarpaulin secured over the damaged area, are commonly used to keep a property watertight until a permanent repair can be carried out. These are holding measures only and should not be relied on for long.
It is worth checking whether storm damage is covered by buildings insurance, as many policies include it. Photographs of the damage taken as soon as it is safe, along with notes on dates and weather, help support any claim. Most insurers expect damage to be reported reasonably promptly and may ask for an assessment from a qualified roofer before authorising work. Keeping a record of what was done to limit further damage is generally useful, because reasonable steps to prevent the problem worsening are usually expected.
Reviewed: June 2026