Water rarely enters a roof where it appears inside. It runs along battens, rafters and mortar before it drops, so a stain in the middle of a ceiling can come from a metre or more away, uphill. That is why diagnosis is the part of a roof repair worth paying for, and why the first visit that only patches the visible mark comes back.
The eight usual suspects
Slipped or broken tiles and slates, which is the obvious one. Failed flashings at a chimney or an abutting wall, especially mortar fillets used instead of proper lead. A split or blocked valley. Perished underlay, so wind driven rain that gets past the tiles is no longer caught. A blocked or overflowing gutter backing water under the eaves. Cracked or missing ridge and verge mortar. A failed rooflight flashing kit. And penetrations such as vents and pipes where the collar has perished. Between them these account for most domestic roof leaks.
Condensation that looks like a leak
A loft that drips in cold weather, shows damp on the underside of the felt, or has black mould on the rafters near the eaves is usually condensation rather than a leak. It follows cold nights rather than rain, and it appears across an area rather than at a point. The cure is ventilation and stopping warm moist air getting into the loft, not a roofer on the tiles. Getting this diagnosis wrong is expensive in both directions.
Ventilation, and the gap that has to stay clear
A cold roof void needs cross ventilation, with a clear path at the eaves on opposite sides, and the guidance expects an unobstructed air gap above the insulation. The commonest defect in British lofts is insulation pushed hard into the eaves, blocking the path it depends on. Eaves trays keep the gap open while letting the insulation run out to the wall plate, which is where it has to reach to avoid a cold bridge. Tile and ridge vents supplement the eaves where the geometry needs it.
Leaking roof repair cost UK-wide: what a repair should give you besides a price
A good repair visit produces a diagnosis, not just a price: where the water is entering, how it was established, what is being done and what is not. Ask for photographs from the roof, which are cheap now and are the only way you will see what was found. Ask what happens if the leak persists, because a competent firm that has diagnosed properly will return, and one that patched a stain will not want to.
When repairs stop being the answer
One slipped tile is a repair. A roof shedding tiles every winter usually has failed nails or perished battens, and patching it rents time rather than buying a fix. Torn underlay visible across the loft, several leaks in different places, mortar failing along ridge and verge together, and a covering at the end of its service life all point the same way. A roof laid well lasts decades; the point to stop repairing is when the third repair in two years is being quoted.
Questions people ask about roof leaks
Why is my roof leaking in one place but the tiles look fine?
Water travels along battens and rafters before it drops, so the entry point is usually uphill of the stain and often some distance away. That is why the diagnosis, not the patch, is the valuable part of the visit.
Is water in my loft always a leak?
No. Damp on the underside of the felt in cold weather, across an area rather than at a point, is usually condensation, and the fix is ventilation and air sealing rather than roof work.
How long should a roof last?
A well laid covering lasts decades and the battens, underlay and mortar work usually reach the end of their lives first. Repeated repairs in different places is the signal that the roof as a system is finishing rather than that you are unlucky.
Can a leaking roof be repaired in the rain?
A temporary covering can be put on in bad weather and a proper repair usually waits for dry conditions, especially where mortar or adhesives are involved. Temporary protection first is the right sequence.