Roof leaks from snow: is it an ice dam or something else?
A roof that only leaks under snow is giving you a clue. The location of the drip tells you most of the story.
If your roof only leaks when there is snow on it, the snow is doing something rain cannot. That narrows the cause quickly. Roof leaks from snow usually come from one of four things.
The commonest cause: an ice dam
Heat from the house melts snow mid-slope. The water runs down, hits the cold eave and refreezes. Ice builds up, water backs behind it and climbs under the shingles. The drip shows up near an outside wall, often with icicles outside.
If that sounds like your house, read our page on ice dam leaks.
Meltwater with no dam at all
Sometimes snow sits on a low-slope section or against a wall and melts slowly. Water has time to find a weak spot in the flashing or a nail pop. The leak appears in the middle of the roof, not at the eave. Look from the ground for staining or a rusted patch where a roof meets a wall.
Wind-driven snow
Fine snow blows through ridge and soffit vents and lands on the attic insulation. It melts when the attic warms, and it looks like a leak. Check the attic with a flashlight from the hatch. A thin dusting of snow near the vents is this.
Heavy snow on a weak spot
Deep snow pushes against flashing and can hold water against it. It also hides problems you would see in summer. You cannot sort that out until the snow clears, so note where the stain is and photograph it.
What to do tonight
Contain the water inside. Move belongings, put a bucket under the drip and keep away from a bulging ceiling. Do not go up to clear the snow or hunt for the hole. We never write steps for working on a snowy roof.
Then call a roofing contractor and tell them where the stain is and whether it is at the eave or mid-slope. That one detail saves a wasted visit.
Frequently asked questions
Why does my roof only leak when there is snow?
Snow holds water against the roof for hours or days. That gives meltwater time to get past an edge or weak spot that rain would run straight over.
Is every roof leak from snow an ice dam?
No. Ice dams are the most common cause near the eaves, but flashing trouble and wind-driven snow in the attic can look the same.
Should I remove the snow from my roof to stop the leak?
Not by climbing up. From the ground, a roof rake can clear the lowest few feet. For more than that, hire a professional with fall protection.
How do I tell snow in the attic from a leak?
Look near the vents with a flashlight from the attic hatch. A fine dusting of snow or frost around the vents is wind-driven snow, not a failed roof.
Sources
What this page explains is based on these official sources. If you check one and it does not match what you read here, send it to us and the article gets corrected.
- NOAA / National Weather Service. Winter — National Weather Service safety hub
- NOAA / National Weather Service. What To Do If You're Caught in a Winter Storm