Ice Dams vs Ice Tunnels



Some of you have asked what is an ice dam, and how does it cause damage. The diagram above sort of says it all but here is the chain of events that lead to the above example.IDIT2

An ice dam is a ridge of ice that forms at the edge of a roof and prevents melting snow (water) from draining off the roof. The water that backs up behind the dam can leak into a home and cause damage to walls, ceilings, insulation, and other areas.


This wintry scene is brought to you by high heat loss. The ice dam at the roof’s edge is damage waiting to happen.

Heat tapes are a good idea for the roof, too. Low-temperature tapes provide constant heat to break the snowmelt and freeze cycles. Ice dams form when snow on warm patches of the roof repeatedly melts, flows downhill and freezes over the cold parts of the roof and gutters. Eventually a large mass of ice forms beneath the shingles or tiles. Snowmelt backs up behind these dams and sits in big puddles on the roof, damaging it and causing leaks.

The problem starts with uneven temperatures on the roof caused by heat loss from the building’s interior, a problem that may require extra insulation to solve. Gaps around plumbing vents and electrical wiring act like chimneys, siphoning heated interior air into the attic. A warm attic heats the roof, melting snow from the top of the roof down.

Spray-foam insulation is a simple and easy way to seal these gaps. Even if there are no gaps visible, additional insulation may be needed to prevent warm air from rising into the attic.

Specialty heat tapes are available to prevent ice build-up in gutters. If gutters fill with ice, they may start to sag from the weight and even break loose from their mountings.

Does insurance provide coverage for damage caused by ice dams? Check your wordings – you probably do, and do not take this exposure into consideration when explaining coverage, or underwriting a risk, or adjusting a loss.


Ice Tunnels are rare but when they happen one must be very careful to remove them. They occur when a metal roof that has adequate insulation and ventilation has a snow build up with a wide spread of temperature in the daytime (very warm) and in the nighttime (very cold). These tunnels can cause extreme damage to the roof, gutters, fascias, and soffits if they go unchecked. What happens is that the snow at the peak on the plane starts to melt exposing the metal roof. The heat from the sun is absorbed by the metal roof heating the roof right down to the eaves and the whole snow pack starts to slowly slide down the roof surface. This only occurs on low slope roofs, if it was a medium or high sloped roof the weight of the snow sliding off the roof would eventually break the piece off that was overhanging. Here because the process is so slow the snow starts to curl and wrap itself under the eaves. As an example, please see below.