Rain on Snow: A Recipe for Disaster

Structural Engineer Tony Coviello Explains Roof Load Dangers

The Blizzard of 2015, popularly called Winter Storm Juno, dumped 2-feet of snow on parts of New England this past week. The immediate forecast is for another storm this weekend. Unlike Juno, this next storm is predicted to be heavy and wet.  Any combinations of deep snow followed by wet snow or rain can be extremely dangerous for roofs.

Structural Engineer Tony Coveillo, one of the principles at Summit Engineering, is cautioning homeowners throughout New England to be aware of the dangers this winter mix could pose in the coming days.

“Snow followed by rain is one of the worst combinations for roofs,” said Coviello. “The problem with rain or wet snow following a deep snowstorm is that the rainwater doesn’t pour off of the roof. It gets trapped in the snow. The increase in weight can get dramatic.”

Coviello further explains that the weight of snow varies depending upon the temperature and moisture content.

“A 12-inch snow depth can weight from 10-lbs to 20-lbs a square foot. It’s the rain on top of this that is the real problem. This last storm probably added close to 30-lbs of snow over each square foot of roof. That’s a very large amount of weight.”

Rainwater weighs approximately 5-lbs for every inch. A significant storm can cause a dramatic increase in weight on roofs that are already stressed by heavy snow and may have not been designed to handle it.

“It is more of a concern for older structures,” explains Coviello. “The building codes over the last three decades have done a far better job of mandating roofs to handle these types of loads. However, older cities in the Northeast have a large portion of their building stock built much earlier than that.”

Coviello recommends that homeowners clear the snow off their roofs as soon as possible. However, he cautions that they should not go onto the roofs themselves.

“Getting on a sloped roof with slippery ice and snow is extremely dangerous. Only remove snow from the ground with a roof rake or hire a professional with the proper insurance and safety equipment,” he stressed.

Summit Engineering is no stranger to investigating building collapses. The firm was heavily involved in the investigation of structures after Superstorm Sandy in New York and New Jersey for FEMA and have worked on a number of insurance claims involving damage from snow.

When asked if he thought this recent storm would cause a large increase in insurance claims, Coviello responded: “It all depends upon this second storm. It could be a very busy winter for us as structural engineers and it is why I will be clearing off my own roof.”