Snow on your roof

From eNews, March 8, 2007

A heavy snowfall can create dilemmas for Minnesota homeowners, who often worry about how much snow their roofs can support or what to do about ice dams and large, hanging icicles.

According to Richard Stone, University of Minnesota Extension housing technology specialist, homeowners are encouraged to hire professionals to clear snow or ice from roofs.

"Homeowners who attempt to clear heavy snow or ice dams by themselves risk serious injury and may damage the roof," says Stone. "If there is not ice build-up at the edges, it may be alright to leave the snow on the roof, and trust that the roof can support the load. Roofs, like the rest of the home, should have been designed to withstand expected snow loads."

In Minnesota, design plans showing expected snow loads are usually required to receive a building permit, says Stone. The plans for your home may be on file at your local building inspection office. To help you understand the plans, or if you cannot find plans for your home, contact an architectural engineering firm. A professional engineer should be able to evaluate the structure of your home and answer questions about the strength of your roof.

Stone also warns homeowners to be cautious about icicles hanging from roofs, which can be dangerous if they fall. Large icicles may also signal the formation of ice dams. An ice dam is a ridge of ice that forms at the edge of a roof, preventing melted snow from draining properly.

Ice dams are often caused as heat escaping from the home into the attic warms the roof surface and melts snow. Melted snow runs downward and hits the cold edge of the roof where the water refreezes. As the ice builds up at the bottom edge of the roof, it creates a dam that causes water to back up under the shingles and potentially leak into the house.

"Damage from ice dams can show up in many forms," says Stone. The most common signs include water-soaked insulation, stained or water-soaked ceilings and water accumulation in wall cavities, causing damage to walls and interior finishes.

University of Minnesota Moment

Everyone knows about shoveling your driveway when it snows, but most people don't know that it might be necessary to clear your roof too--in particular if it is an agricultural building. University of Minnesota Extension professor Larry Jacobson explains.

How should a homeowner deal with ice dams?

• Removing an ice dam can place the roof and the ice dam remover at serious risk. Hire a professional who has the equipment and experience to clear the ice dam safely and with less risk of damaging the roof.
• Stay away from large icicles, if there are any, to avoid injury--should they fall.

Over the long term, or in preparation for next winter, here's what homeowners can do:

• Make ceilings airtight so no warm air can flow from the house into the attic space. However, you should evaluate the impact these changes will have on exhaust ventilation systems and the safety of combustion devices like furnaces and water heaters.
• Increase your ceiling or roof insulation to cut down on heat loss.
• Proper roof ventilation also helps maintain uniform attic and roof temperatures.
• Contact a weatherization professional to help you develop safe and effective solutions. (Look in the Yellow Pages under "energy management," "conservation consultants" or "insulation contractors.") Your electric or gas utility company could also help you locate a contractor. Contractors use diagnostic tools to detect places where heat and moisture are escaping from the house into the attic space, creating the potential for ice dams. They can then fix the problem areas and improve home efficiency.

For more information on ice dams, see the Minnesota Department of Commerce Energy Information Center.