Preventing Ice Dams
Tips for protecting your home and your possessions in the winter
Ice dams are formed on your home’s roof when ice builds up over the eaves and pools of melted snow back up and seep under the shingles of the roof. The water and ice can then cause damage to both the exterior and interior of your home. Although using a roof rake to remove snow from over the eaves of your house may be a short-term solution, prevention is the key. Here are a few tips to help you identify and prevent ice dams.
Causes
In most cases, ice dams begin inside the house, when heated air leaks up into an unheated attic. That creates warm areas on the roof, which in turn cause snow on the exterior of the roof to melt. The melting snow slides down the roof slope until it reaches the cold overhang or gutter, where it refreezes.
The process continues, causing ice to build up along the eaves and it forms a dam. Eventually this dam forces water to back up under the shingles and sometimes into the ceiling or wall inside the home. The moisture related to that build up can result in decay to structural framing members, corrosion of metal fasteners, and mold and mildew in attics and on interior surfaces.
Goals
The goals are to keep the warm air in the living space of your home from seeping into the attic and maintain a cool, well ventilated attic space that will not cause the roof to warm up.
Identification
Ice dams are often hidden under a blanket of snow at the edge of the roof. So, careful and periodic examination of the roof is essential.
If after a snowfall the roof is bare near the peak, but snow-covered toward the eaves with icicles hanging off, it is probably ice damming.
All types of overlapping shingles including asphalt, wood, slate and tile are susceptible to ice dams and should be examined for buckling. Check your attic for signs of moisture, mold or mildew, insufficient insulation and inadequate ventilation.
Prevention
Improve the ventilation in the attic by unplugging roof vents that may be blocked or by adding new vents.
Add insulation to the attic floor, plug holes in existing insulation and block the flow of warm interior air into the attic.
Sources of heat leakage into the attic that may need addressing include:
- Ceiling light fixtures.
- All plumbing and heating penetrations including chimneys, vent pipes and ducts.
- Attic hatches and pull-down stairs.
- Dropped ceilings over bathtubs, closets and cabinets, and kitchen soffits.
- Areas where walls are not completely sealed at the attic, such as stairway walls and interior partition walls.
- Electrical and telecommunication equipment cables, electrical boxes and fan housings, such as exhaust fans.
- Skylights.
