Roofing Glossary

Ice Dam

An ice dam is a ridge of ice that builds up along the lower edge of a roof — typically above the gutters — and traps melting snow behind it. The trapped water pools and backs up under the shingles, leaking into the house. It is one of the most destructive winter roof problems.

Dams form through a cycle: heat escaping into the attic melts snow on the upper roof; the meltwater runs down to the cold eaves (which extend past the heated house) and refreezes into a growing ridge. Each day's melt adds to the dam until standing water is deep enough to push under shingles — and shingles are designed to shed flowing water, not resist standing water.

The permanent fix is stopping the heat loss: attic air sealing, adequate insulation, and balanced ventilation to keep the roof deck uniformly cold. Ice-and-water shield along the eaves provides backup protection.

Why It Matters

Ice dams are a symptom of heat loss, not a roofing defect — which means a new roof alone will not cure them unless the attic issues are fixed at the same time.

What to Watch For

• Thick icicles spanning the gutter line
• A visible ice ridge with slush pooled behind it
• Ceiling stains near exterior walls after a thaw

A Maryland Note

Maryland's freeze-thaw winters — melting by day, freezing by night — are ideal ice dam conditions. See our full ice dam guide for what to do.

Questions about your own roof? Request a free estimate or call Nucci Brothers Roofing at (301) 458-1003.