The hazards of Ice Dams
What is an ice dam?
An ice dam is a ridge of ice that forms at the edge of a roof, cricket,
or valley that prevents melting snow (water) from draining off the roof.
The water that backs up behind the dam can leak into the home and cause
damage to walls, ceilings, insulation, and other areas.What causes ice dams?
There is a complex interaction among the amount of heat loss from a house, solar energy, snow cover, and outside temperatures that leads to ice dam formation.The dam grows as it is fed by the melting snow above it, but it will limit itself to the portions of the roof that are on the average below 32°F. So the water above backs up behind the ice dam and remains a liquid. This water finds cracks and openings in roofing materials and flows into the attic space. From the attic it could flow into exterior walls or through the ceiling insulation causing substantial damage to the interior of the home.
What causes different roof surface temperatures?
Heat from the house travels to the roof surface in three ways:
conduction, convection, and radiation. In a house, heat moves through
the ceiling and insulation by conduction. The resulting higher
temperatures in the attic are then transferred to the roof sheathing by
radiation.Penetrations in the home’s ceiling, such as light fixtures, allow heat to escape to the attic space. In many homes this is the major mode of heat transfer that leads to the formation of ice dams.
Exhaust systems like those in the kitchen or bathroom that terminate just above the roof may also contribute to snow melting. Other sources of heat in the attic space include chimneys. Frequent use of wood stoves and fireplaces allow heat to be transferred from the chimney into the attic space. Inadequately insulated or leaky duct work in the attic space will also be a source of heat. The same is true for kneewall spaces.
Preventing Ice Dams
Until recently, the traditional method of reducing ice dams has been to install self-regulating heat cable in a zig-zag pattern along the roof eave. This method can be ineffective, particularly in very cold climates and in areas of heavy snow accumulation. Traditional "Zig-Zag" cables are not designed to clear the entire roof edge, especially under heavy winter conditions. Other concerns about “Zig-Zag” wire is that it is very inefficient, costly to operate, and susceptible to damage from sliding snow, tree branches, and other roof hazards.Roof De-icing systems are one of the best investments homeowners, builders, and business can make to protect against ice damage and personal injury. Innovative new systems are now available that will clear away snow and ice from critical areas of the roof. Expand the life of your roof and reduce the risks associated with snow and ice by installing a well designed roof de-icing system.
