Ice dams in Colorado: why ventilation matters more than heat cable

Every winter, we get calls about water dripping from ceilings near exterior walls after a snowstorm. The culprit is usually an ice dam: a ridge of ice along the eaves that traps melting snow behind it. That water backs up under shingles and finds its way inside. Heat cable can help in specific spots, but it treats the symptom. The real fixes are in your attic.

How ice dams form

Heat escapes from your living space into the attic. If the attic is warm, it melts the bottom layer of snow on the roof. Meltwater runs down the slope until it reaches the eaves, which hang out past the warm walls and stay cold. There it freezes. Each day the ice ridge grows, and water pools behind it.

Denver's sunny days after snowstorms make this worse. Strong sun melts snow on the upper roof by day, and temperatures drop sharply at night.

The three-part fix

1. Seal air leaks and add insulation

Warm air leaks through recessed lights, attic hatches, plumbing chases and bath fans. Sealing these and bringing attic insulation up to current recommendations (often R-49 to R-60 in Colorado) keeps heat where it belongs.

2. Balance ventilation

A properly vented attic stays close to outdoor temperature. That requires both intake at the soffits and exhaust at the ridge. Many homes have ridge vents but soffits blocked by insulation, or plenty of soffit vents with too little exhaust. We calculate net free area for your attic and balance the two, usually with about half intake and half exhaust.

3. Ice and water shield at the eaves

Code in most Front Range jurisdictions requires self-sealing ice and water shield membrane at the eaves. It seals around nails, so even if water backs up, it has a much harder time getting inside. On north-facing slopes or low-pitch roofs, we often extend it further up the roof.

Where heat cable fits

Heat cable can be useful on problem areas that cannot be fixed with ventilation, such as a low-slope valley or a north eave over an entry. It should be installed in a zigzag pattern with a run through the gutter and downspout so meltwater can escape. It uses electricity all winter and does not address the underlying heat loss.

What to do if you have an ice dam now

• Do not chip ice with a hammer or axe. You will damage shingles and gutters.
• Use a roof rake from the ground to pull snow off the lower 3 to 4 feet of roof.
• Place calcium chloride ice melt in a sock across the dam to create a drainage channel. Do not use rock salt, which damages shingles and plants.
• Call a professional for steam removal on large dams.

Plan the permanent fix

The best time to fix ventilation is during a roof replacement, when the deck is open and ridge vents can be cut properly. If your roof is newer, we can still add soffit baffles, seal attic bypasses and improve exhaust. A free inspection includes an attic check and ventilation math, and you will get a clear list of fixes with prices.

A cold attic, a sealed ceiling and ice and water shield at the eaves will do more for your winter than any length of heat cable.