It Only Leaks in Heavy Rain
This is a useful clue, not a mystery. A roof that handles light rain but fails in a downpour is telling you the problem is volume, direction or a detail that is only marginally adequate.
The four usual explanations
- Volume — a blocked or undersized gutter backs water up under the shingles at the eave. Light rain drains; heavy rain does not
- Wind direction — driving rain pushes water sideways under shingles and into details that gravity alone never reaches
- A marginal detail, such as a short head flashing above a skylight or dormer, which only gets overwhelmed at high flow
- Valleys dammed with debris, which carry light rain fine and overflow sideways in a storm
Why this type is often misdiagnosed
It cannot be reproduced with a hose at low flow, so a contractor who tests casually will find nothing and tell you the roof is fine. Then it rains properly and your ceiling stains again.
Testing has to match the conditions: high volume, and from the direction the weather actually comes from.
Check your gutters first
This is the cheapest thing on the list and a common cause. Sacramento collects eight months of debris and then receives its entire annual rainfall in concentrated storms — a gutter that coped in October is frequently full by December.
Clear them, then see whether the next storm reproduces the leak. That one step resolves a meaningful share of these calls.
Common questions
Why does my roof only leak in heavy rain?
Usually volume or wind direction rather than a hole — a backed-up gutter, a dammed valley, or a detail that is only just adequate and gets overwhelmed at high flow. It is a clue worth telling whoever inspects the roof.
Can gutters cause a roof leak?
Yes. A blocked gutter backs water up under the shingles at the eave, and it only happens at volume — which is exactly the pattern of a heavy-rain-only leak.