The short answer
A roof can still leak after a repair for five main reasons: the water is coming from a second source, the repair missed the true entry point, damp already in the house is still drying, a stopgap has failed, or the repair itself was not sound. Note when and where it drips, take photographs, and contact the roofer with those details. A written guarantee gives you a clear route.
First, is it really still leaking?
Water that has soaked into plaster, insulation or timber does not vanish the moment the roof is mended. It dries slowly, and a stain can darken, spread slightly or even drip a little in the days after a repair, particularly in damp weather when the air in the house is humid. That is a drying house, not a failed repair.
The way to tell is to watch the pattern. A stain that stays the same size and slowly fades is drying. A stain that grows, a fresh drip that appears during or just after rain, or a new patch in a different place suggests water is still getting in. Mark the edge of the stain in pencil with a date, and check it after each spell of rain. It sounds fussy, but it gives a roofer something solid to work with, and it spares you arguing from memory about what the ceiling looked like last week.
Ceiling bulges, dripping from light fittings and visible running water are signs of an active leak. Treat those as urgent, and keep clear of any ceiling holding water.
The repair fixed one leak but not the other
Many roofs have more than one fault. A repair that cured the worst one may leave a second, smaller one that only shows in certain winds or storms. This is common after a long-running leak, because the first obvious cause drew attention and the quieter one was never looked for.
Water also travels. It can enter at a flashing, run down a rafter or along the underlay for a metre or more, and appear far from where it got in. A roofer who repairs the place where the stain is, rather than where the water enters, will find the leak carries on. Our page on finding a roof leak explains why the entry and the stain are often some distance apart.
Heavy rain can show up a weakness that lighter rain did not. If the leak returns only in storms, our page on why a roof only leaks in heavy rain may fit what you are seeing.
A stopgap that has failed
Some repairs were never meant to last. Sealant, a bitumen daub or a tile slid in unfixed can hold for a few weeks and then give way. If the repair was described as temporary, or was very cheap and quick, a recurring leak is not a surprise. Our page on roof sealant repairs explains why they tend to fail.
The remedy is the proper repair that the stopgap was standing in for. It is worth being clear with yourself about what you paid for. If you were told it was a permanent fix and it was only sealant, say so when you contact the roofer.
Damp from the house, not the roof
Some damp ceilings are not roof leaks at all. Warm, moist air from cooking, bathing and drying clothes rises into a cold loft, meets cold surfaces and condenses. The result is damp patches, mould and drips that appear on cold days without any rain. A roof repair will not touch them.
The clue is timing. Condensation tends to follow cold, still weather and affects the colder parts of the roof, such as the corners of the ceiling and the cold side of the felt. It often clears in warmer, drier spells. A leak follows rain. Our condensation or leak page sets out the tests, so check it before you conclude the repair failed.
When the repair was not sound
Sometimes the work itself is at fault. Tiles may have been replaced without proper fixing, a flashing dressed too shallow, or a new valley lining laid with short laps. Workmanship problems appear soon after the work, usually in the first rain, which is the point of a guarantee.
If you think the repair failed, stay off the roof yourself. Photograph it from the garden and from inside the loft, note the date and weather, and contact the roofer. Then look at the paperwork. Our guarantee on repairs runs for 10 years in writing, and it rests on the business, not on an insurer.
How to use a repair guarantee
A guarantee is only useful if you can act on it. Find the written copy and check the period, what it covers and who to contact. Then get in touch promptly, with dates, photographs and a plain description of where and when water appears. Hold off hiring a second firm for the same spot until the first has looked, since that blurs who is responsible.
A fair guarantee covers the workmanship of the repair, so a fault in the work done will be put right. It does not cover a different fault elsewhere on an old roof, or new damage from a storm. Our roof repair guarantee page explains those limits in more detail, and our how long a roof repair takes page covers the timing of a return visit.
Cold weather can delay a return visit, and our winter roof repairs page looks at what can be done in poor conditions. If a Skyline repair is not holding, ring 01793 626096 or use the enquiry form, say when and where it leaks, and see the roof repairs hub for related questions.