Ice deposits and icicles form when snow melts, goes down the roof, and freezes again near the edge. This only occurs when part of the roof is heated above 32 degrees F, hot enough to melt snow, while the roof edge remains below freezing. This scenario is usually the result of a warm attic. Ice buildup can be prevented by controlling home heat loss.
Eventually, ice accumulates along the eaves, forming a dam. The meltwater from the warm roof accumulates behind it, flows under the shingles and enters the house. Stopping ice dams is not that difficult. Preventing ice build-up starts with keeping the roof at the same temperature as the eaves.
This can be achieved by adding insulation, increasing ventilation and sealing all outdoor air leaks. Ice buildup occurs when water from melted snow runs over the surface of a roof and freezes again. Melting snow is caused by warm air in the attic space that heats the lower part of a roof. Fluctuating temperatures can also influence the creation of snow melt.
Ice dams form on the underside of roofs, allowing water to penetrate and cause damage to the interior of walls and ceilings. When snow melts on a roof, it runs down until it reaches the unheated lower edge of a roof and then freezes. This piece of ice is called an ice dam and can cause water to build up under shingles and ice dams to damage walls and roof structures. Pre-season prevention measures, such as a subfloor for roofs that specifically protects against rain and ice dams or thermal bands in drains and downspouts, can significantly reduce this risk.
The most common way ice builds up is when there is a loss of house heat combined with snow cover and low outside temperatures. The theory is that the age of the roof was a contributing factor that the ice dam could cause damage to the interior of the house. In cases where the ice dam goes unnoticed for an extended period, it can cause significant damage to the building and its contents. In other words, you must do everything possible to eliminate any existing ice dam and prevent future ice build-up in the long term.
The best roofing contractor will also install several feet of an ice and water protective product to help protect against water damage due to ice dams. If damage caused by the formation of ice dams were isolated from the outside of your home, you'd be lucky. However, there is a good chance that your home insurance will cover damage caused by a problem with an ice dam. The last thing you want is for your home to be the victim of a problem with an ice dam right in the middle of the sales process.
If you look up and see a large chunk of ice on the lower edge of your roof, your forensic work is done; you have an ice dam. As the “pond” accumulates in the ice dam, the water seeps back under the shingles and seeps into the roof eaves or into the house. Usually, your insurance provider will issue you a check minus the deductible to repair damage caused by the ice dam. Whether or not you have identified an ice build-up problem, this indicates that you have a thermal bridge problem.
The first and most important approach to controlling ice dams is to reduce the amount of heat loss in the attic, as this will help keep the lower part of the roof cool.