LEARN
Why Does My Flat Roof Only Leak When It Rains Hard?
If your roof is fine most of the time but leaks during a big storm, that’s actually useful information — here’s what it usually means.
It’s a Good Sign, Not a Bad One
A roof that leaks only during heavy rain, and stops between storms, usually points to a specific, localized defect — a marginal seam, a flashing gap, or a low spot that only overflows once rainfall exceeds a certain rate. That’s a very different, more repairable situation than a roof failing across its entire surface.
Berkeley gets the bulk of its roughly 23 inches of annual rainfall concentrated between November and March, with December typically the wettest month. When an atmospheric river moves through, a marginal detail that’s held fine all summer can suddenly leak for what feels like the first time — even though the underlying weakness has probably been there a while.
What’s Actually Happening
Heavy, sustained rain does a few things a light drizzle doesn’t: it overwhelms drains and scuppers that were coping fine with lighter volume, it saturates and expands any marginal caulking or sealant until it finally gives way, and it creates ponding that puts sustained pressure on a low spot in the membrane. All three point to a findable, fixable defect rather than a roof that needs full replacement.
Frequently Asked Questions
Should I wait until the rainy season ends to get it fixed?
No — the defect is there year-round, it just isn’t stressed enough to leak in dry weather. Getting it diagnosed and repaired before the next storm is the better move.