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Why You Should Shovel the Snow Off Your Roof
Office of the State Fire Marshal 2-10-15

The weight of snow varies from one area of the state to another.  The light fluffy snow may only weigh about seven pounds per cubic foot while more average snow may weigh 15 to 20 pounds per cubic foot depending on how compact and saturated it is. Snow drifts due to the fact they are compacted would probably be at the higher amount closer to 20 pounds per cubic foot.

Roofs are designed to carry the normal snow load for a specific location as specified in the State Building Code. However, the design load is having the snow spread out equally across the roof.  The recent snowfall in combination with the wind has caused snow on one side to be clear and the other 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 none off the other will have the same effect.

A simple way to determine the weight of the snow at your location is to use a piece of PVC pipe with a cap to push down to the base of the snow for a sample of the snow. Then upright it and let it melt. When the snow melts if you have 8 inches of water in the PVC pipe it equals 41 pounds per square foot and would go up or down with each inch of water by 5.2 pounds. This is a rough estimate figure and should be used with caution.

If you are not sure of the capacity of your roof, consult with a structural engineer to review the design of your roof structure.

If you think your roof may have been compromised, consult with a reputable builder and your local building official.

There are potential dangers of shoveling or raking snow from a roof, besides the collapse danger. There are the dangers of a person sliding off the roof, falling from a ladder, overexertion, or falling snow sliding on top of them.

Roofs that are flat also have a maximum snow load they can carry. With flat roofs it is important to keep the roof drains clear of snow, leaves and ice.

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. 

The decision of an individual property owner should consider the dangers against the benefits of removing the snow in determining their course of action.

Remember the rule of thumb that condensed saturated snow weighs about 20 pounds per cubic foot and keep in mind the design capacity of your roof structure.


State Fire Marshal Warns of Building Collapse Danger
Office of the State Fire Marshal 2-05-15

State Fire Marshal J. William Degnan announced today that due to recent heavy snow there is a greater urgency to clear roofs of 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.  High roof parapets can accumulate significant drifting snow, especially during wind events.

The following warning signs could indicate that you have a danger of roof collapse.  You should immediately evacuate the building and notify your local building official, fire department, or contact a structural engineer to determine if the building is safe if you observe the following:



*       Sagging roof steel - visually deformed

*       Severe or new roof leaks

*       Cracked or split wood members

*       Bends or ripples in metal supports

*       Recent cracks in walls, drywall or masonry

*       Cracks in welds of steel construction

*       Sheared off screws from steel frames

*       Sprinkler heads pushed down below ceiling tiles

*       Doors that pop open

*       Doors or windows that are difficult to open

*       Bowed utility pipes or conduits attached to the ceiling

*       Creaking, cracking or popping sounds


Past fire investigations have determined that gas service to some buildings have been damaged due to heavy snow loads and snow sliding off of roofs onto gas meters and components.  Also snow sliding off of roofs onto outside oil tanks has caused valves and filters to be broken off.   The State Fire Marshal urges all citizens to do the following:

*       Clear roofs of excessive snow and ice buildup, being careful not to damage gas and oil service to the building.  Clearing the roof can be dangerous and should be left to professionals.  Using a roof rake is recommended while keeping away from electrical lines.

*       Keep all chimneys and vents clear to prevent carbon monoxide from backing up into the building.  Some vents, such as 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.

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 223-4289.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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