An ice dam forms when heat escaping into the attic melts roof snow that refreezes at the cold eave, and the backed-up meltwater works under the shingles. The water comes in through the roof and the ceiling, not through the basement. Call (833) 490-5225 and a technician will trace the leak from the attic down.
Key takeaways
- Heat escaping into the attic melts roof snow, which refreezes at the eave.
- Water enters through the roof and the ceiling, not the basement.
- The Wisconsin Historical Society suggests net free ventilation of one square foot per 150 square feet of attic floor, split between soffit and roof, plus air sealing.
- Photograph the ceiling stain and the attic before anything is moved.
How do ice dams cause roof leaks in southern Wisconsin?
Warm air rising from the house melts the snow on the roof, and the meltwater runs down to a cold eave and freezes into a ridge of ice. The ice holds back the next melt, which finds its way under the shingles.
Heavy snow followed by a long cold stretch is what keeps a dam in place. The leak then appears on the ceiling of the top floor, often at an outside wall or a corner where the insulation is thin.
The Wisconsin Historical Society's guidance on attic ventilation and air sealing is the practical starting point for preventing a repeat.
What should I check after a ceiling leak from an ice dam?
Check the ceiling below the stain, the attic insulation and the roof edge. Water that has soaked insulation keeps wetting the ceiling after the thaw.
Keep people and pets out of the room under a bulging ceiling. Wet plaster and drywall can come down in one piece without warning.
A technician measures the ceiling and the framing and opens only the smallest section needed to see how far the water travelled. Roof repair is a roofer's job, and the crew does not replace the roof.
Frequently asked questions
Is an ice dam leak a basement problem?
Usually not. Ice dam water enters through the roof and the top-floor ceiling. A basement wet from the thaw is a separate problem with a separate source.
Can I knock the ice dam off myself?
Be careful on a ladder in snow. Keep people off the roof edge, and call (833) 490-5225 for the water in the house while the roof is handled by a roofer.
Sources
- Wisconsin Historical Society, ice dams and attic ventilation
- National Weather Service, Milwaukee/Sullivan climate and snowfall
This guide is general information for Jefferson County homeowners, not a substitute for an on-site inspection. Prices are estimates. See our disclaimer.