Ice dams form when heat from the inside of the home escapes into the attic and warms the roof decking in the winter. The heat, combined with heat from the sun, can melt snow on the roof. Melting snow on the upper roof and in the valleys, runs down to the eaves as water. When it reaches the cold eves and gutters, it refreezes. The continual thaw and refreezing creates Ice Dams. Resulting in water and ice backing up under the shingles and/or fascia boards. where it can then soak through decking or wall sheathing, causing damage to attics, ceilings, and walls.
Ice dams along the roof plane can add an extreme weight load to the roof structure as well as the gutter system. This is noticeable after the spring thaw, and your gutters are bent, sagging , or literally falling off the house. Depending upon the height and roof pitch, having them professionally removed, can be quite costly, ranging in the area of $100.00 to $500.00, depending on the situation.
Prevention: If you address your insulation, and ventilation you will be ahead of the game with close to a 90% success rate when done properly. Attics should have cross ventilation. Natural venting from the soffits (soffit vents), to the top of the roof, via ridge vents or more traditional roof vents. Recommended venting is at least 1 sq ft free venting to every 300 sq ft of attic floor area. Power ventilators are another option, but should be controlled for humidity as well as heat. Trying to acquire cross ventilation, with a somewhat circular air flow through the attic. This will help to prevent heat buildup in the attic and the snow melting on the roof, causing water to turn into the dreaded Ice Dams.
Dave
November 20, 2010
Tis the Season. Well almost. Old man winter and the snow that comes along with it is just around the corner. And although attic ventilation should be thought about year round, Ice Dams are the worry in the colder climates. A proper balanced ventilation system can help prevent ice dams, as well as help maintain a comfortable climate indoors. Ice damming can cause serious damage to the roof sheathing, soffits, fascia, and cause water intrusion to the interior of the home as well. Ventilation is one of the best ways to prevent dams by creating a “cold” roof. Roof design can determine what style of ventilation is best for your roof. In some cases good ventilating of the attic is all but impossible, without rebuilding the roof structure itself. Power vents and/or wind turbines can help. And as a last resort snow raking the roofs, at least five feet above the roof eves, or heat tapes applied to this same area can be the answer. I could ramble on for a long time, but to save time I found a pdf put out by Air Vent INC. that is a good reference on the issue and has some really good and detailed information on ventilation. Please take a look at this and you too will be well informed.
(right click then open in new window)
Dave
October 11, 2010