With winter weather well under way, we can't help but raise our eyes to our roofs, and notice the snow piling up. The snow is getting deeper, and as the weather begins to creep out of freezing, the addition of rain or snow melt into the mix can become a real threat. While all exposed roofs could be at risk, older flat roofs and roofs with poor drainage are the most susceptible to collapse due to snow.
Newer roofs should have been designed for the minimum snow load as prescribed in the International Building Code, and the ASCE 7 – Minimum Design Loads for Buildings and Other Structures. Typically in the Berks County area, the design ground snow load is 30 pounds per square foot (PSF), which equates to just over 20 inches of dense snow. Additional snow load needs to be considered where snow from an adjacent sloped roof can slide onto a lower roof. Also, additional load from drifting snow must be considered when portions of the roof abut parapets, roof top equipment or higher roofs. Lastly, rain-on-snow surcharge can add 5 PSF for every inch of rain that is retained on the roof by the snow or poor drainage.
If you think your roof is at risk, you should contact a structural engineer to evaluate your roof condition. It may be necessary to remove some of the accumulated snow, clear roof drains, or provide temporary shoring to lessen the burden on the structural members. The removal of snow can be very dangerous, and is a job best left to a professional.