What is an Ice Dam?
Ice dams cause millions of dollars of damage every year. Obvious, visible damage may include sagging ice-filled gutters, rotted roof decking, stained or sagging drywall, damaged shingles, and wet insulation. Unfortunately, obvious damage may be just the tip of the iceberg. The worst effects of ice dams are often hidden, caused by moisture trapped inside walls or floors. This damage is seldom discovered until months after all the snow has melted.
Ice Dams are Caused by the Interaction of Three Factors:
- Ice and snow melt at 35° F. Liquid water freezes at 32° F. Minor temperature differentials can lead to major problems.
- Layered roof systems such as shingles do not keep out standing water. They require a continuous, uninterrupted slope to shed water.
- Attics are warmer than the outside air because heat leaks from the heated portion of the structure up into the attic. Heavy snow cover effectively insulates the attic from cold outside air, allowing the temperature to rise even higher.
Eventually, the temperature of the roof under the snowpack, usually near the ridge, rises above the melting point. Meltwater runs down the roof, refreezing when it reaches the edge of the insulating snow blanket at the soffit/eaves. They are still far below the freezing point since they are unheated by air from the structure interior. An ice dam forms. As layer after layer of melt-water refreezes, the ice dam grows, with liquid water pooling behind it under the snow. Soon, this water is deep enough to seep back up the roof and between shingles where it can leak into the attic or wall cavities. Secondary ice dams often form around vents and skylights.
Prevention: The Cold Roof
The best protection against ice dams is a properly designed "cold roof." Minimizing heat gain in the attic while maximizing attic ventilation with outside air is the best way to reach this goal. Attics gain heat in two main ways: inadequate insulation and warm air leaking through gaps.
- Reduce heat gain by increasing the insulation levels, meticulously caulking and sealing even the smallest penetrations through the ceiling, as well as carefully gasketing around attic en-trances. Although some heat gain is inevitable, when the attic ventilation is adequate the temperature will not reach levels that cause extensive melting.
- Install iceguard (Self-sealing rubberized membrane installed under shingles) as an additional line of defense against penetration. This is an effective backup to a cold roof approach, but requires re-roofing.
What Should I do if I Have an Ice Dam?
Once an ice dam forms, the only relief is to remove the ice and snow from the roof. This is extremely dangerous work and often results in the roof being damaged. Unfortunately, it is typically best to let the ice dam melt on its own. Your best course of action is to limit as much damage as possible by poking a hole in the ceiling in the area where it is leaking to cause a controlled drip into a bucket or pan. Once the ice dam is gone, immediate setps need to be taken to dry out the structure to prevent additional hidden damage to your home. Our infrared camera will help determine the extent of the hidden damage and allow us to take the steps necessary to properly dry out your home.
Damage: Obvious & Hidden
Ice dams cause millions of dollars of damage every year. Obvious, visible damage may include sagging ice-filled gutters, rotted roof decking, stained or sagging drywall, damaged shingles, and wet insulation. Unfortunately, obvious damage may be just the tip of the iceberg. The worst effects of ice dams are often hidden, caused by moisture trapped inside walls or floors. This damage is seldom discovered until months after all the snow has melted. The homeowner seldom makes the connection between the damage found and their ice dam of the previous winter. In addition to the cost of restoration, hidden damage can even create serious health risks for building occupants.
Hidden damage is entirely preventable. With proper instruments, equipment and training, trapped moisture in building materials can be detected and removed before it causes severe damage.