Answers · Is something wrong?
Why does my roof only leak in heavy rain?
The short answer
Because most roof leaks are not holes. They are places where water is designed to run past and only overtops or blows back when the volume or the wind is high enough — valleys, flashings, penetrations and gutters. That is why a roofer goes to those four before looking for a puncture.
The four usual causes
- Gutters overflowing. Water backs up under the edge of the roof and into the fascia and soffit. It looks exactly like a roof leak from inside and it is a cleaning job.
- Valley detail. Where two slopes meet carries the most water on the roof, and a valley that was cut short, nailed through, or laid without the right underlayment leaks only at volume.
- Flashing at a chimney, a wall or a skylight. Sealant instead of proper step flashing is the classic shortcut, and sealant has a service life measured in a few years.
- Wind-driven rain, which pushes water uphill under shingles and sideways through vents. If the leak correlates with wind from one direction, say so — it is genuinely diagnostic.
What to record before anyone comes
- The weather each time it leaks: heavy rain, wind direction, temperature.
- Photographs of the stain, dated, so you can see whether it is growing.
- Whether it stops when the rain stops, or continues for hours afterwards, which points at water held somewhere.
Also asked
- Can a roof be repaired in the rain?
- A temporary make-safe can be, and reputable contractors do it after storms. A permanent repair usually cannot: sealants and underlayments need a dry substrate, and anyone promising a permanent fix on a wet roof is promising a second visit.
General information about roofs and about hiring, not advice about your building. Roofing contractor licensing, permits, insurance practice and deductible rules are set state by state and province by province across the United States and Canada, so your own authority is the current answer.