An ice dam is a ridge of ice along the bottom edge of the roof. Snow melts higher up, the water runs down, and it freezes again when it reaches the cold eave. Once the ridge builds, meltwater pools behind it and can back up under the shingles and into the house.
Why they form
The usual cause is heat escaping into the attic. A warm attic warms the roof deck, which melts the snow from underneath, even on a cold day. The overhang at the eaves stays cold, so the water refreezes there. Lincoln winters, with snow followed by sunny days and freezing nights, are good at setting this up.
Signs you have one
- A thick lip of ice along the gutters or eaves
- Big icicles, especially with water dripping behind them
- Water stains or peeling paint on ceilings or walls near outside walls
- Wet insulation or frost in the attic near the eaves
What to do right now
- Stay off an icy roof. Falls are the real danger here
- Clear snow from the lower few feet of the roof with a roof rake, from the ground
- Don't chip at the ice with a hammer or axe. That damages shingles
- If water is coming in, catch it and take photos for your records
What fixes it for good
Long-term fixes keep the roof deck cold so snow doesn't melt unevenly: sealing air leaks from the house into the attic, adding insulation, and making sure the attic is vented from soffit to ridge. When a roof is replaced, an ice and water barrier membrane along the eaves helps keep backed-up water out. A roofer can look at your attic and roof edge and tell you which of these your house needs.
Leaking now? Get a Lincoln roofer to call you.