Forecasters had warned of an epic blizzard, and for coastal Connecticut, Rhode Island, and Massachusetts, the warning wasn’t just hype. The blizzard, unofficially dubbed “Nemo” by the Weather Channel, brought the fifth-deepest snowfall in recorded history to Boston. In parts of Connecticut, the storm set new records, bringing accumulations of three feet or more. Portland, Maine’s 29-inch total also set a new record. At the storm’s peak, utilities reported 600,000 customers without power. But this was just a small fraction of the millions blacked out by Hurricane Sandy in October.
One hazard in any heavy snowstorm is that accumulating snow may pose a risk to vulnerable roofs — especially if warming weather and rain follow on the blizzard’s heels. As the storm approached, Coastal Connection talked with engineer David Grandpre, an expert in building structural failures with CA Pretzer Associates, an engineering firm based in Cranston, R.I. Grandpre is active with the Architects and Engineers Emergency Response Task Force of the Structural Engineers Association of Rhode Island, and he’s a member of the Rhode Island Urban Search and Rescue Team, organized to work with the state Emergency Management Agency in case of building collapses that trap people or endanger lives. With the storm looming, Granpre said, he and other experts were on call to respond in case of catastrophe.
The state-level team that Grandpre belongs to serves a particular need: “This is a good example,” he says. “If we have a snow event and if we have people trapped, and it’s hard to travel, we’ll have local trained people with specialized equipment on site as fast as they can drive the vehicle to the location. We have dogs to help search for people, and the whole thing.
Two years ago, New England saw widespread roof collapses when heavy snows were followed by rain (see “Heavy Snowfall Threatens New England Roofs,” Coastal Contractor 2/2011). Whether roofs fail this time around depends on specifics of the weather, Grandpre explained — as well as on the special vulnerabilities of particular buildings.
“Current building codes required designers to address snow drifting, but older building codes did not address snow drifting. So older buildings are only designed for whatever the ground snow loads are, without that extra 100 pounds you can get where high roofs and low roofs meet and cause snowdrifts to build up.” In the 2010 and 2011 storms that created a rash of roof failures, there wasn’t a remarkable amount of drifting snow, Grandpre says. But in storms like this weekend’s blizzard, with 30 to 40 mph winds and gusts to 65, “each building is going to be unique with respect to the windward and leeward sides of the storm. “So if a particular building that was not designed for drifting has the low roofs that are going to accumulate the drifting snow on the leeward side of this particular storm, then they have never been tested like that before. So those will be the most vulnerable roofs.”
“For the most part,” says Grandpre, “these weather events weed out the weak. In the 2010 and 2011 storms, for the most part, only buildings that were faulty failed. Good buildings, built according to codes, don’t fall down in weather events.”
Storms that bring two feet of snow are rare. When you add variable wind direction, buildings can go many decades without experiencing a particular kind of drifting. “The remarkable blizzard of 1978 caused a lot of roof failures,” Grandpre points out. “But if this storm blows wind from a slightly different direction, and creates drifting that wasn’t experienced in those storms before, then this could be the storm that eats that building.”
And with rain falling on the coast Monday afternoon, scattered roof failures were reported. Connecticut realtor Kristin Geenty lost a nice listing when a 186,000-square-foot commercial building’s roof in Clinton fell in. “The warehouse had been vacant for about 16 months,” she said in an email, “but it was very well maintained. Unilever closed it about 8 years ago, and we subsequently leased it to Wal-Mart and a logistics firm for Tempurpedic Mattress.” In all, the Torrington (Connecticut) Register Citizen reported eight collapses in the state by Monday afternoon (“8 roof collapses reported so far in Connecticut”), including two barn collapses that resulted in the deaths of some cows. In Smithtown, N.Y., on Long Island, a bowling alley roof caved in (fortunately, without injury).
In the event, however, the high winds may have been a net benefit for roofs in the region. With temperatures well below freezing, the weekend’s snows were mainly light, easily blown flakes. And for most roofs, that meant that the wind blew the roofs clear, reducing the risk posed by any subsequent rain.