What Causes Icicle Formation on Roof Eaves?

Common Causes

• Most often, icicles form on roof eaves due to heat escaping through the roof. Heat may escape because the attic isn't adequately insulated, and it could also be that the attic floor isn't properly sealed, allowing warm air from the home to escape into the attic and through the roof. Other sources of heat loss that can contribute to roof snow melt and icicle formation are chimneys and vents that pass through the attic. Inadequate attic ventilation may also allow heat buildup in the attic.

The Best Solution

• The best way to reduce icicle formation on roof eaves is to address the source of the problem. Often in old houses, improving attic insulation and sealing leaks is sufficient. Also consider sources of heat loss specific to your home; for example, if duct work runs through your attic, it may need additional insulation. These improvements will not only reduce ice damming and icicle formation, they'll also make your home more energy-efficient and reduce your utility bill.

  If your attic is sufficiently insulated and sealed but doesn't have good ventilation, consider getting an attic fan, which will remove heat from the attic and reduce heat loss through the roof, as well as improve comfort and save cooling energy in the summer. Don't add an attic fan, though, without first ensuring that your home has adequate sealing between the living space and attic.

Quick Fixes

• Some companies offer roof tape and other devices to prevent ice dams and icicles by melting the snow on roofs before it has a chance to melt and refreeze. These solutions are usually effective at preventing ice dams, but they treat the symptom, not the problem. Quick fixes such as this cost more money in the long run because they use additional electricity to heat the outside of your roof in winter, rather than fixing your home to waste less heat energy and solve the icicle problem at the same time.

Damage

• A few small icicles are usually harmless on a roof, but when ice damming occurs, it could cause roof and wall damage. An Ice dam prevents water from draining off the roof properly, and it can force water back up under shingles and into the home, where it can cause structural damage to the roof, walls and interior by warping and rotting wood.

Safety

• If you have an ice dam forming on your roof eaves, you may be tempted to knock it down or chip away at it to protect your roof. This, however, is quite dangerous because it can cause falling icicles or cause you to slip and fall if you're working on top of the roof. Manually removing ice dams can also damage roofs. Although still dangerous, it's safer to rake or shovel snow off your roof before an ice dam forms.