There’s a flurry of activity on the rooftops following every big snowstorm, as homeowners scramble to reduce the snowload on their roof. A damaged or collapsed roof is certainly a worst nightmare for any building owner, but when do you really need to peel yourself away from the woodstove and do some scraping? It’s a matter of quality: both of the snow, and of the roof.
Barrett Proctor owns Proctor Properties in Hancock, and does his fair share of snow removal during the winter. He said there’s no exact rule to when he’s called out to clear roofs, but he’s typically called out to work on flatter roofs, or roofs that are lower quality, like a makeshift garage – or whenever televised news starts recommending that homeowners shovel their roofs.
“As soon as the news starts to say it, I get phone calls,” he said.
Rain events after a lot of snow are a recipe for a very heavy burden on the roof, he said.
Peterborough Fire Chief Ed Walker agrees: “The snow traps the rain in the roof, by both absorbing it and blocking drains, and the extra weight causes the collapse. He said that several roofs collapsed across the state last year due to snow.
Snow ought to be removed when its weight exceeds half the live load capacity of their roof, typically expressed in pounds per square foot, according to guidelines from the New Hampshire Public Risk Management Exchange. Landowners can determine their roof’s live load capacity through its as-built plans, or with a structural engineer. Moderately wet snow is often estimated to be one pound per square foot per inch of depth, although extremely wet snow can weigh twice as much. So, for a roof with a live load capacity of 20 pounds per square foot, it’s advisable to start clearing moderately wet snow when it’s ten inches deep, or very wet snow at five inches deep.
Roofs are more susceptible to collapse if the roof is flat or slightly sloped, or lacks drainage, or features a long span, like in some commercial buildings like garages or auditoriums. Additionally, roofs over unheated or intermittently heated buildings are at higher risk for collapse, as are roofs that are poorly maintained or have collapsed before.
A roof is at increased risk for collapse if it leaked during the previous winter or spring, if water is pooling in places where it never has before, or if it’s made “popping” noises (indicating that rivets have broken). Ripples or bends in metal supports, cracks in wooden members, or obvious deformations are also indicators of increased risk.
As with anything involving roofs, ice, or both at the same time, safety is imperative.
“Residents should make sure it is safe to remove the snow from roofs, especially pitched roofs, to prevent personal injury,” said State Homeland Security and Emergency Management Director Jennifer Harper.
The Office of the State Fire Marshal advises that homeowners remove snow from the ground with a rake whenever possible, and never work on a roof or on a ladder alone. Additionally, its recommended to not clear snow during strong winds, call 911 for any electrical wires that a snowstorm might have brought down, and to keep room drainage systems clear of snow to prevent the risk of roof ponding in the event of heavy snow melting.
To protect the roof while he’s clearing it, Proctor said that he doesn’t use metal shovels, and never digs down to the shingles. He said he’s begun to use snow rakes more.
“They’re so easy,” he said.
Brands like Avalanche feed a silicone tarp underneath the snow to help is slide off effortlessly.
Proctor also said to be aware of where the cleared snow lands, and to plan time for additional snow removal. He said nothing’s worse than having to clear a roof just to move the snow two or three more times to keep it from leaning on windows, or out of a driveway.