Do You Need to Shovel Your Roof When It Snows?

Roof Load

• The first thing to know is how much of a load your roof is designed to bear. Modern structures that have been issued a building permit for construction are required to hold at least 40 pounds per square foot, according to the city of Coeur d' Alene in Idaho. Older houses may have roofs that were not built to that standard. Contact your city zoning department to find out what the local standards are. Roof load is the number to keep in mind. If the snow exceeds that, it's probably time to think about shoveling.

Calculations

• The moisture content of snow can vary greatly, containing anywhere from 1 to 33 percent moisture. To err on the side of safety, you might choose to go with the higher number and assume that the snow weighs about 21 pounds per cubic foot. This rule of thumb means that 1 foot of snow on your roof is probably not a reason for concern, but if the snowfall reaches 2 feet in depth or higher, there's a good chance the weight is reaching the theoretical threshold of the roof's weight-bearing capacity.

Safety

• It's easier to say you're going to shovel snow off the roof than to actually get up there and do it. There are obvious personal injury and property damage risks, from falling off a ladder to straining your back to sliding off the roof to causing shingle damage with the shovel. The bottom line is to not worry about climbing up there in adverse conditions unless it's absolutely necessary. If you have doubts about your own physical ability to safely perform the task, there's probably a spry young neighbor nearby who would be glad to help out.

Considerations

• Many areas have the bonus of ice accumulation to go with their winter snowfall, and this additional weight should be taken into account. In general, you can figure that an inch of ice weighs about 5.2 pounds per square foot, so if you have an inch of ice under your snow, don't forget to factor in its weight as well. Remember that a flat roof holds more moisture than a pitched roof, so you might choose to provide a broader safety buffer when calculating how much of a load it will bear.