WEST DES MOINES, Iowa –Snowfall in February has been historic. Jonathan Whitford, Valley High School’s Athletics Custodian is all too familiar with his shovel. “I’ve been told that we have five miles worth of cement sidewalks so that is a lot of work,” he said.
Fortunately for him, the West Des Moines school district along with Des Moines Public School District leave the roofs alone thanks to their buildings’ ability to hold snow. “The codes did not include required designs for drift loading prior to the 1980`s,” said Shive Hattery Senior Structural Engineer Steve Brase. He says the drifting happens when snow leaves a taller roof, and adds weight to a shorter roof. “Sometimes those loads can get upwards to 100 pounds per square foot,” Brase said.
A design that can leave a school vulnerable to a roof collapse from snow usually comes with building expansion. “If you put in a new addition that is taller than an existing building adjacent to it they need to go into the older structure and make sure it is satisfactory to take drift that it never would have seen in the original design,” said Brase.
That is what keeps these school roofs strong and keeps Jonathan from roof duty. “It’s cold up there, the winds really whip up there,” said Jonathan.
School districts can even save on insurance through OSHA testing proving their buildings are designed to withstand drift loads even after expansions. Brase said, “They’ll come in and point this out to them and say you need to get your roof checked for snow drifting.”
Building codes also determine how much drift loading a roof should be allowed to handle based on the heights of different roofs.