With recent winters bringing polar vortexes and record snowfalls, many homeowners are overwhelmed with their first experiences dealing with damaging ice dams. Fortunately, when you understand what causes an ice dam, you can take steps to prevent one from happening. What causes ice dams?
Ice dams occur when ice or snow on a roof melts, then trickles to the edge of the roof and refreezes. This happens when heat inside the home escapes to the roof, causing snow to melt from below and refreeze along the eaves. The result is a thick ridge of ice along the edge of the roof and the gutters. Ice dams can also accumulate at vents, skylights, and any point where two parts of the roof meet.
The resulting icicles may look pretty, but the thick ice keeps melting snow from draining through the gutters the way it should. Instead, water finds alternate routes into the home. The resulting leaks can damage interior walls, ceilings, and insulation, which can quickly lead to expensive repairs. Water trickling down the side of your home can also seep into your exterior walls and damage your home's structure and siding as it refreezes. Is my home at risk for ice dams?
Although the winter cycle of snow and freezing temperatures is completely outside your control, several aspects of your home play an enormous role in your risk for developing an ice dam. Assess your home's ice dam potential in late summer or early fall so you can stop problems before they have a chance to start.
- Make sure your roof gets plenty of afternoon sun. This helps snow melt naturally from above. Have a professional remove or cut back limbs or other vegetation that excessively shade your roof.
- Ensure proper insulation inside your attic. To prevent excessive melting from the underside of the snow layer, your attic should keep a consistent, cool temperature throughout the winter - generally between 5° and 10°F warmer than the temperature outside. To do this, you will need an adequate layer of insulation to prevent the heat from the living area of your home from warming the air in your attic. Exactly how much you need depends on the R-value, or thermal resistance, of your insulation and the climate where you live - the Department of Energy has a guide to insulation that will walk you through the process. Also make sure that light fixtures, chimneys, attic hatches, vent pipes, and exhaust fans are properly sealed as those are all common places for warm air to escape.
- Ensure your roof has adequate ventilation to prevent the formation of ice dams. Soffit vents under the eaves and ridge vents at the peak of your roof combine to keep cool air circulating through your attic. These vents should be clear and unobstructed all year round, but this is especially important during winter. A lack of ventilation will cause your roof to warm, melting snow and encouraging the development of ice dams. Check your attic to make sure nothing is blocking your soffit vents. Walk around your home and look under the eaves, soffit vents are installed underneath, between the gutter and the side of your home. You can usually see the ridge vent from inside your attic as it typically looks like a gap in the wood material of the roof covered with a dark roofing fabric.
Although it's possible to add soffit vents yourself, most homeowners prefer to leave this to a contractor, and adding ridge vents is definitely a job for a roofer. If your home has cathedral ceilings or your attic is a finished living space, speak to a licensed roofing contractor to confirm how your roof is ventilated.
When adding insulation, take care not to block the air flow from your soffit vents. Additional vents inside the rafters can keep air flowing while allowing you to place insulation all the way to the edge of the attic floor. How can I prevent ice dams?
If your home is prone to ice dams despite having adequate ventilation and insulation, or if its structure makes it impossible to adequately ventilate the roof, other products can significantly reduce the formation of ice dams.
Managing through the winter season
- Heat cables installed along the eaves are effective at melting ice. These should be installed by a trained professional to reduce the risk of exacerbating the problem by melting ice too quickly.
- Ice and water shields can be professionally placed underneath shingles to provide an extra layer of protection from melting ice. The rubberized material allows water and ice to run right off the roof, unlike the standard felt paper. This is ideal for areas around skylights and in valleys where two sections of the roof meet.
- Homes can also be retrofitted with snow and ice slides, which are sound options for people who've struggled with ice dam issues before. These are placed on top of the shingles, usually by a professional contractor. Slides keep ice dams from coming in contact with the roof surface near the gutters and eaves.
When winter weather begins, if your home is only one story, use a roof rake to remove all snow from about 3 feet back from the roof's edge, where ice dams are most likely to form. Getting onto the roof is dangerous, so only try to remove snow yourself if you can safely do so from the ground. Also, use only tools designed to remove snow and ice from the roof, using any other tool will damage your shingles.
Ice from a melting dam can back up in unexpected ways. So, if one does form on your roof in spite of these precautions, contact a professional to remove it rather than trying to do it yourself.