State Fire Marshal J. William Degnan announced today that with the recent snow, 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. The recent snow has impacted several structures in the seacoast in Portsmouth, Seabrook and Hampton. The impacts range from structural compromise, total building collapse to blocked venting for the heating system.
Buildings that can be considered most at risk are ones where the snow load is not even across the roof with large accumulations of snow and ice, buildings with large open floor areas, storage, warehouses, flat or low-sloped roofs and unoccupied buildings. The factors that also contribute to the potential of collapse of these structures are ice dams, frozen or clogged roof drains, structural design issues, and damage to structural components. The balance of the snow load is also a major element to consider as having the weight all on one side of a rood can cause excessive loading and possible collapse.
The weight of accumulated snow and ice is critical in assessing a roof’s vulnerability. The water content of snow may range from 3% for very dry snow to 33% for a wet, heavy snow, to nearly 100% for ice. An inch of water depth weighs 5.2 lbs. per square foot and can be measured by taking a uniform vertical column of snow from the snow surface to the roof surface and measuring the death of the water when melted. Thus your roof snow load carrying capability is critical to determining when to clear your roof.
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 along with gas and oil service to the building.
- Keep all chimneys and vents clear to prevent carbon monoxide from backing up into the building. Some vents, such as gas and oil heaters 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.
- Working on or near a roof to clear snow can be very hazardous. Make sure you have good footing and a safety line if you are on a roof, stay clear of the fall zone for snow and ice that is coming off a roof. Use a company with people that are trained to work on roofs whenever possible.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. For information on roof snow load requirements in your community, view the report at the following website link; http://www.senh.org/wp-content/uploads/2010/12/tr02-6.pdf
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