Most flat roof leaks come from flashing (around chimneys, vents, skylights and parapets), a clogged drain that lets water pond, or a cracked membrane at the end of its life. If it leaks: protect the inside, cut power near the water if needed, take photos and get a roofer quickly.
On a flat roof, water can travel far before showing up, so the stain is not always under the leak.
The 5 most common causes
- Flashing: where the membrane changes direction. See flat roof flashing.
- Clogged or frozen drain: leaves, debris or ice block the water.
- Ponding water: poor slope creates puddles that wear the membrane.
- Aging membrane: cracks, blisters, missing granules.
- Punctures: equipment, aggressive snow removal, falling branches.
What to do in the first hours
- Protect the inside: bucket, tarp, move furniture.
- Electrical safety: shut off the circuit if water reaches a fixture or outlet.
- Document: photos and dates for your insurer.
- Stay off an icy roof: let a pro check the drain and membrane.
- Call a roofer: a temporary fix keeps insulation and drywall dry.
If water reached the insulation, fast drying limits mould: see our water damage restoration page. Prevent the next leak with our pre-winter checklist.
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General advice. For any electrical or structural risk, call a professional right away.