Mid-Atlantic Region Sweeps Skylights Clear to Prevent Further Storm Problems
February 19, 2010

East Coast residents will go into the snowstorms forecasted for early next week with a number of lessons learned from last week’s record-breaking snow, including the importance of removing snow from skylights. In many cases, problems such as the one faced at the start of the storm by the Richmond, Va., City Hall (CLICK HERE for related story) can be prevented if the necessary steps to remove snow and ice are taken.

“Building owners and maintenance engineers need to be aware of the design loads of the skylights and sloped glazing and take the precautions and actions for removal,” says industry consultant Greg Carney, president of C.G. Carney and Associates Inc., who describes a condition known ice damming.

“Additional load and safety concerns are created when there’s ice on a roof or other sloped surface. The process of the snow and ice thawing during the day and refreezing as temperatures drop during evening hours results in what is commonly called ice damning,” explains Carney. “Ice damning is a concern for both commercial and residential roofs, skylights and sloped glazing as the condition can lead to water penetration as well as structural damage or failure. So it’s an issue of load factors, but also of retaining ice and water.”

According to Chuck Anderson, codes and industry affairs manager, for the American Architectural Manufacturers Association, ASTM E1300 deals with the resistance of glass due to snow. He explains it does so by rating the resistance to long duration loads (30 days); the required design snow loads for a given geographical location come from ASCE 7.

“A lot of commercial building packages have a standard snow load rating of 30-40-50 pounds per square foot (psf), so somehow you have to convert the inches of snow on your roof to psf. Since not all snow is created equal I personally know of building owners weighing a square foot of snow on their roofs to give them a comfort level with the integrity of the building,” says Anderson. “Load resistance of a flat glass skylight could be calculated by an engineer with all of the parameters given to him.”

Anderson also says that, in theory, a Durst chart could be used to convert the DP rating of the product to a long duration load, but it might be overly conservative because the glass resistance is probably a lot higher than the DP rating.

“Additionally, not many skylights carry a label, so it will be hard to identify what is in the opening,” says Anderson, who adds that it’s not just skylights that can be a concern. “Awnings are also at risk, as well as the main roof. A heavy rain can really make the snow weigh a lot, and scuppers are likely blocked.”

News reporters have advised East Coast residents that the cumulative snow weighing down their roofs can lead to significant damage, such as the Smithsonian faced when the rooftop of an offsite storage facility collapsed last week (CLICK HERE for related article).

And Carney adds, “Given the recent weather conditions, building owners and maintenance engineers would be wise to take the necessary steps for removal. Also, as snow begins to melt they will also need to take into consideration situations where ice and chunks might fall off buildings and can cause injuries. So it’s a safety consideration, too.”

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