An ice dam is a ridge of ice that forms at a roof’s edge, typically at the eave, when heat escaping from the attic melts snow higher up on the roof while the colder eave area, extending beyond the heated living space, remains cold enough for that meltwater to refreeze into an ice ridge.
This ridge of ice can then trap subsequent meltwater behind it, creating a pool that has nowhere to drain except potentially backing up under the shingles and into the roof structure, a genuine and often costly cold-climate roofing problem.
Ice dams are fundamentally caused by uneven roof surface temperature, meaning addressing the underlying insulation and ventilation issues that create this temperature disparity is more effective than simply removing ice after it forms.
What Causes Ice Dam Formation?
- Inadequate attic insulation allowing heat loss to the roof deck
- Insufficient attic ventilation trapping warm air near the roof
- Uneven roof surface temperature between heated and eave sections
- Snow accumulation providing the meltwater source
Why Are Ice Dams Important?
Water trapped behind an ice dam has no clear path to drain and can back up beneath shingles, working its way into the roof deck, attic insulation, and eventually interior ceilings and walls, causing damage that’s often expensive to repair and sometimes not fully apparent until significant deterioration has already occurred. This water intrusion risk makes ice dams a genuinely serious concern rather than merely an unsightly winter nuisance.
Addressing the root cause, typically through improved attic insulation and balanced ventilation to keep the entire roof surface at a more consistent, cold temperature, is a more effective long-term solution than repeatedly removing ice dams after they’ve already formed each winter.
Ice Dam vs. Ice Damming
Ice dam refers to the physical ridge of ice itself. Ice damming describes the broader process and phenomenon of ice dams forming and causing water backup, essentially the verb form describing the same underlying cold-climate roofing issue.