Roof problems
Ice dams: why they form and how a new roof helps
Ice dams form when heat from the house melts snow on the upper roof and the water refreezes at the colder eaves, building a ridge of ice that backs water up under the shingles. The lasting fixes are keeping the attic cold, with better insulation and ventilation, and protecting the roof edge with ice and water shield, which Connecticut’s building code requires from the eaves to at least 24 inches inside the exterior wall.
Updated October 3, 2026
- What it looks like
- A ridge of ice along the gutters, heavy icicles, and water stains near the tops of outside walls after a thaw.
- What it usually means
- Heat escaping into the attic melts snow higher up, and the water refreezes at the cold eaves and backs up under the shingles.
- How urgent
- Act on any stain right away. Water behind an ice dam reaches walls and insulation.
- What to do next
- Pull snow off the bottom few feet of the roof from the ground with a roof rake, and photograph any stains. When the roof is replaced, ask how far the ice and water shield runs. On Thomas Roofing’s Core and Complete options it covers the whole roof.
How an ice dam causes a leak
Shingles shed water that flows downhill. Water trapped behind a ridge of ice sits still and works its way up and under the shingles, then through the deck into walls and ceilings.
Signs you have ice dams
- Thick ice along the gutters and eaves
- Large icicles, especially over windows
- Water stains near the tops of exterior walls after a thaw
- Snow melting on the upper roof while the eaves stay frozen
What a roof replacement changes
- Ice and water shield from the eaves to at least 24 inches inside the exterior wall, required by Connecticut’s building code, which seals around nails and keeps backed-up water out
- Full ice and water coverage on our Core and Complete options
- A ridge vent that lets warm, moist air out of the attic
- A chance to check soffit vents and insulation while the deck is open
Keeping the attic cold
Ice dams start with heat. The building code’s baseline for attic ventilation is 1 square foot of vent opening for every 150 square feet of attic, or 1 for every 300 when 40 to 50 percent of the vent area sits high on the roof (International Residential Code R806.2). Air sealing and insulation on the attic floor matter as much as the vents.
What to do now
- Don’t chip ice off the roof, because it damages shingles
- Pull snow off the lower few feet of the roof from the ground with a roof rake
- Watch for ceiling stains and photograph them
Questions
- Will a new roof stop ice dams completely?
- A new roof with ice and water shield stops ice dams from causing leaks at the edge. Preventing the ice itself depends on keeping the attic cold, which comes down to insulation and ventilation.
- How far up the roof does ice and water shield have to go?
- Connecticut’s building code requires it from the lowest edge of the roof to a point at least 24 inches inside the exterior wall. Many roofs get more: our Core and Complete options cover the whole roof.
Sources
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