Ice Damning – An Overview

August 29th, 2012

Did you ever find your attic soaking wet and cold after a particularly bad winter? Have you ever seen ice slowly and steadily enveloping your house from the lower edges of the roof to the gutters? If your answer is yes then you already have a fair idea of what ice damning is. How does it happen? Ice damning usually happens during heavy snowfall. Due to heat loss, the rooftop is warmer (more than 0 degree). This causes the ice to melt and flow down the shingles to the roof overhang. The overhang, which is again colder and at the same temperature as the outside air, causes the water to freeze and accumulate at the edges of the roof and there starts an ice dam. An attic that is not insulated won’t suffer from ice damning and an attic well insulated with modern insulation material is also immune to this problem. Good insulation will create an effect similar to a detached garage where the roof is cool and there is not much melting. Old and faulty insulation with air leaks will result in ice damning during heavy snowfall. Detect the early signs Carefully observe your roof during early frost. If the snow melts in a horizontal line across the roof in an area where the kneewall meets the roof, your house could suffer from ice damning. If the roof has a large overhang or it has a lot of dormers, it could trigger an ice dam. Insufficient ventilation will tend to melt the ice on the overhang and again create an ice dam. Blown insulation seals the air and is more efficient at stopping ice damning than soffit insulation, which has very less ventilation space. How to prevent it? The basic principle of preventing ice damning is maintaining a perfect balance of conduction, convection and radiation, which prevents heat loss through your roof. As an immediate measure, remove ice from the roof or at least create channels through the ice where the molten snow can flow down. For a more permanent solution, seal all air leakage channels between your house and the attic. You should also think of increasing the R value of your insulation to the optimum value of 39 by upgrading your insulation material. If you can maintain a natural ventilation system in your attic space, you can prevent heat buildup during the summer and avoid ice damning during the winter.