State Fire Marshal J. William Degnan announced today that with the recent snow and wind, there is a greater urgency to clear roofs of excessive snow and ice that has accumulated. A roof may collapse with little or no warning, and one common misconception is that only flat roofs are susceptible to collapse.
When should the snow be cleared from my roof?
The depth and weight of snow varies greatly from one area of the state to another.  Roofs are designed to carry the normal snow load for a specific location as specified in the State Building Code (www.senh.org/wp-content/uploads/2010/12/tr02-6.pdf). The design load is having the snow spread out equally across the roof.  The recent snowfall, in combination with high winds, may cause snow on one side of the roof to be clear and the other side to have a large drift which causes an imbalanced load on the roof making it more susceptible to collapse. Also, bear in mind taking all the snow off one side, but not off the other, will have the same effect. The rule of thumb is that condensed saturated snow weighs about 20 pounds per cubic foot. What is the design capacity of your roof structure?
While it is still early in the season, there is no better time than now to make the assessment so you can plan to protect your property.  If you are not sure on the capacity of your roof, consult with a structural engineer to review the design of your roof structure. If at any time you think your roof may have been compromised, consult with a reputable builder and your local building or fire official.
The State Fire Marshal urges all citizens to do the following:
Clear roofs of excessive snow and ice buildup, being careful not to damage your roof or any gas or oil service-entrance or vent into the building below.
Keep all chimneys and vents clear to prevent carbon monoxide from backing up into the building.  Some vents, such as gas, oil, and pellet stove vents, may exit the building through a wall and are susceptible to being blocked by excessive snow buildup on the outside of the building.
Keep all exits clear of snow, so that occupants can escape quickly if a fire, or other emergency should occur. Keep in mind that windows should be cleared to allow a secondary means of escape in case the primary means of escape is blocked by fire. Keeping exits clear also allows emergency workers to access your building.
REMEMBER: Shoveling or raking snow from a roof presents additional hazards with regard to a person sliding off the roof, falling from a ladder, overexertion, or having falling snow slide on top of them.
The State of New Hampshire provides this information in order for property owners to make an informed decision as to when they should consider removing snow from a roof.  An individual property owner should always consider all of the associated dangers in determining their best course of action.
Specific fire and building safety questions can be answered by local fire and building officials or by contacting the State Fire Marshal’s Office at 603-223-4289.