MTS #2 - WHY ICE DAMS CAN DAMAGE YOUR HOUSE The Cause of Ice Dams . Ice dams are a buildup of ice on a roof. They typically occur at the roof edges, usually filling in the rain gutters and working their way up the roof. They can also form large icicles hanging from the eaves and gutters. Ice dams require a balance of warm and cold conditions to occur. This occurs when an insulating layer blanket of snow builds up on a roof. This usually requires several inches of snow. The problem occurs most often at the corners of roof valleys where snow builds in the valleys. The insulating snow traps heat escaping from the attic and causes it to melt along the roof under the snow. If the outside temperature is just right, it is cold enough outside to cause the water to freeze to ice but still warm enough to let water melt under the snow. Studies in Canada have found the ideal outside temperature to form ice dams is about 22 o F. When it is very warm or very cold, ice dams do not occur. This figure is from the Canada Mortgage & Housing Corp web site: www/cmhc-schl.gc.ca
Why Ice Dams Can Damage Your House
Dec 25, 2015
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MTS #2 - WHY ICE DAMS CAN DAMAGE YOUR HOUSE
The Cause of Ice Dams. Ice dams are a build-‐up of ice on a roof. They typically occur at the roof edges, usually filling in the rain gutters and working their way up the roof. They can also form large icicles hanging from the eaves and gutters.
Ice dams require a balance of warm and cold conditions to occur. This occurs when an insulating layer blanket of snow builds up on a roof. This usually requires several inches of snow. The problem occurs most often at the corners of roof valleys where snow builds in the valleys. The insulating snow traps heat escaping from the attic and causes it to melt along the roof under the snow. If the outside temperature is just right, it is cold enough outside to cause the water to freeze to ice but still warm enough to let water melt under the snow. Studies in Canada have found the ideal outside temperature to form ice dams is about 22 oF. When it is very warm or very cold, ice dams do not occur.
This figure is from the Canada Mortgage & Housing Corp web site: www/cmhc-schl.gc.ca
House with ice dam in roof valley. Infrared camera showing cold spot (blue) by door. Removing the baseboard showed wet insulation and the wall dripping water from the ice dam above.
How Do Ice Dams Cause Damage? As ice dams build, they can wedge their way under roof shingles and through gaps in panels. As the water melts, it is often forced to drip down inside the ceiling and inside the walls. This not only reduces the insulating value but leads to mold, musty odors and wood rot inside the wall cavity. In some cases, portions of a ceiling may collapse.
Photos showing ceiling & wall damage from an ice dam. Visible black mold present.
How Can You Check for Ice Dam Damage? Walls and ceilings next to and under ice dams can be checked by opening up wall cavities or baseboards. Infrared cameras and moisture meters can help check for damage before opening up wall cavities. Be careful when opening up wall cavities as this may disturb mold.
Moisture meter used to map out wet wall (“X” area) caused by ice dam. Sensitive “deep” green meter detecting dampness in some areas where standard (shallow) moisture meter does not.
How Can Ice Dams Be Removed? It can help to remove the insulating snow from the roof and roof valleys. Some contractors use steam or hot water to melt away ice dams. Removal can be dangerous and physical removal may damage the roof or gutters.
How Can Ice Dams Be Avoided? It helps to keep the attic cold, well insulated and well ventilated. For attics, an R value of 38 or more is recommended (about 2.5 ft of blown in fiberglass insulation.
Left photo. Well insulated attic (2-3 ft insulation). Red is ceiling light Top of insulation 34 oF. Right photo. Warm attic, 50 oF . Insulation about 1 ft thick. Both photos taken in winter. Outside temp 20 oF.
Ice dam summary, page 3
Hot spots can occur at vent pipes, attic hatches, poorly insulated heating ductwork,etc. Ceiling lights may give off lots of heat. These hot spots should be located and properly insulated or sealed off. Infrared cameras can help to locate hot spots.
Good roof ventilation is important. Soffit vents should not be plugged over with insulation. Airflow should be able to enter under the eaves into the soffits and out through vents near the ridges. Inside the attic (with the lights off) visible light should be seen coming from the soffit vents.
Left photo shows baffle in attic at roof eave to keep soffit vent from being plugged. Right photo shows plugged soffit vent when blown in insulation added. This caused water drips inside the house.
Contractors may offer other suggestions as well. Heating wires can be laid in a triangular manner along the roof edges. Rubber membranes can be installed along the roof edges under the shingles to help keep out melting water and ice. See your contractor.
How Can Damage Inside the House Be Minimized? When ice dams occur, take steps to remove snow and ice outside. On the inside, opening up walls may help but must be done carefully to avoid stirring up airborne mold. Raising the heat and reducing the humidity sometimes help (may not work for walls with plastic vapor barriers). Cleaning firms can sometimes drill small holes and insert drying tubes. See your local cleaning firm for options.
Drying should be done as soon as possible. Extensive mold growth may occur within a few weeks after the weather begins to warm. Drying may also help minimize wall and flooring damage,etc.
This summary provided by Mike Meyer, Mold Testing Services, LLC., Sioux Falls, SD. Ph 605-951-4857. E-mail [email protected]. We provide dampness (moisture meters and infrared cameras) and mold testing (MTS handout#2 - 3/2/10).
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