What Are They?

Ice dams can form on roofs in the winter months and can result in costly water
damage to the interior of a structure. The ice dams form when water freezes on a cold spot on a roof, usually at the eaves. Water that pools behind the ice dam can eventually work its way through the roof covering into the structure.

What Causes an Ice Dam?

Three conditions must be present for an ice dam to form:

  • Snow on the roof ice dam diagram
  • Heat to melt the snow
  • Cold to re-freeze the melted snow

Snow on the roof insulates the underlying snow which is in contact with the roof. Warm air in the attic warms the roof under the snow, causing the snow to melt. The melted snow water then trickles down the slope of the roof, until it comes in contact with the cold edge or eaves area. The snow melt re-freezes in the colder area.

Prolonged freeze/thaw cycles allow the water to build up in the cold region of the eaves to form an effective dam of ice. With ice accumulation, the dam retains enough melt water behind it to allow the water to work its way
under the roof covering, resulting in water entering the structure. Water can then make its way to the ceiling and/or run down the walls. Deep snow followed by frigid temperatures will increase the likely hood of ice dams.

Preventing Ice Dams:

You can’t control outside air temperature, but you can eliminate the snow or eliminate the heat.

  • Take the time to remove snow from the lower eaves or end of rafter area. Without built up snow you have eliminated the source for an ice dam to form.
  • Seal warm air leaks from interior rooms to the attic. (This will also cut your heating bills.)
  • Ensure that you have adequate insulation in the attic. Homes in the Northern United States should have at least R 38 (about 12 inches of fiberglass or cellulose) above the ceiling.
  • Be sure there is unrestricted air movement under the roof from the eaves soffit to the ridge
  • Clean the roof gutters in the fall after the foliage has fallen. Though clogged gutters do not create ice dams, they can cause ice to back up onto the roof. ice dam

If An Ice Dam Develops:

Remove all of the snow from the roof. This can be accomplished by shoveling,
or by reaching up from the ground with a long-handled rake. Use caution so that you don’t fall off the roof when shoveling, or get hit with a chunk of ice if you are raking the snow off the roof.

Too Much Snow On Your Roof?

Structural damage can occur when the weight of snow and ice exceeds the load-bearing capacity of your roof. This is most often the case with flat roofs, older buildings, or structures whose integrity may already be compromised.

Q. How do I know if there is too much snow and ice on my roof?

A. Generally, if there is more than a foot of heavy, wet snow and ice on your
roof, you should try to have it removed.

Q. How should I remove the snow and ice that has accumulated from my roof?

A. If you have a flat roof that is easily reached from an interior stairway, you may want to shovel the roof. Remember to put safety first any time you are on a roof. If you have a sloped roof, it may be possible to remove the snow and ice using a roof rake, a long-handled tool designed specifically for this purpose. Stand on the ground and pull as much of the snow off the eaves as you can safely reach. It is not necessary to remove all the snow; removing the first three to four feet of snow closest to the gutters will help alleviate these issues.
Do not use a ladder in snowy and icy conditions. This can be extremely dangerous and is best left to professionals.

Q. What if I can’t reach the roof at all?

A. Many homebuilders, landscaping and roofing contractors, and property maintenance companies will remove snow and ice from roofs. Before hiring a contractor, check references. Always be sure your contractor is insured and bonded.

More information on ice dams can be found at the University of Minnesota’s website.

*Source: The Hartford Financial Services Group, Inc.