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What Is Ice Damming and How Can It Affect a Roof?
An ice dam is a ridge of ice that forms at your roof's eaves — and it's one of the most destructive winter phenomena a Colorado roof faces. The dam itself isn't the problem. The problem is the pool of meltwater trapped behind it, with nowhere to go but up under your shingles.
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What ice damming is
Here's the sequence: heat escaping through your roof melts the snow on the upper roof. Meltwater runs down to the eaves — which extend past the warm house and stay below freezing — and refreezes into a ridge of ice. More meltwater arrives, pools behind the ridge, and since shingles are designed to shed water flowing down, not to hold back a standing pool, water wicks up under the shingles through capillary action. The result: soaked underlayment, stained ceilings, damaged insulation, and eventually rotted decking.
Why it happens: heat loss, not bad shingles
Ice dams are primarily a ventilation and insulation problem. Warm air leaking into the attic — through gaps around lights, hatches, and ductwork — warms the roof deck unevenly. The fix is keeping the attic cold: air-seal the ceiling plane, insulate adequately, and ventilate with balanced intake (soffit) and exhaust (ridge) so the whole roof stays near outdoor temperature. If your roof melts snow in stripes while the neighbor's stays white, your attic is talking to you.
The damage it causes
- Interior water damage — stained ceilings and walls, damaged paint and drywall.
- Soaked insulation — wet insulation loses R-value, which worsens the heat loss that caused the dam.
- Decking rot — repeated wetting rots the plywood/OSB at the eaves.
- Gutter damage — the ice mass itself can tear gutters loose.
Prevention and the ice-and-water shield
Long-term prevention is attic work: air sealing, insulation, ventilation. The roofing-side defense is ice-and-water shield — a self-sealing membrane installed under the shingles at eaves, valleys, and penetrations that seals around nail holes and blocks backed-up water even when a dam forms. It's standard on quality Colorado installations. What doesn't work: chopping at the dam (damages shingles), or heat cables as a sole fix (they treat the symptom).
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FAQs
Should I knock icicles off my eaves?
Icicles themselves are mostly cosmetic, but big icicle formations often signal an ice dam behind them. Don't chop at ice on the roof — you'll damage shingles. Address the attic heat loss instead.
Do metal roofs get ice dams?
Less often — snow tends to slide off metal before dams build — but they can still form at valleys and low-slope sections, especially with poor ventilation.
Related reading
- How Snow and Ice Affect Colorado Roofs — winter's full toolkit
- How Roof Ventilation Works — the attic fix behind ice dams
- How to Prepare Your Roof for Colorado Winter — the fall checklist
- All roofing guides — browse the resource library
Ice dams staining your ceilings? Fix the cause.
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