by Greg Neiderer, PE, Principal and Director of Restoration, Philadelphia office
Winter snows are here again, and we wanted to share tips for keeping this winter’s storms uneventful for parking structure owners. Parking decks are typically designed to support both typical snows and cars parked on the roof. So why do we hear of snow-related parking deck collapses in the news?
First, new snow is light, often weighing about 12 pounds per square foot for every foot of depth. And while the specific snow load requirements for parking decks vary by geographic location, most decks are designed for a snow depth greater than 18 inches. Often structures can hold much greater depths of fallen snow, especially when there are few or no cars on the roof. So why do collapses occur?
The most common reason is plowing and piling the snow. Plowing densifies the snow, increasing its weight per cubic foot. Then, this heavier snow is often placed into large piles. It is these concentrated loads, much heavier than cars, that cause problems. Snow removal firms are mostly familiar with slab-on-grade parking lots where big piles are not a problem and often not aware that parking structures are not designed for large piles.
For those parking decks where the roof is at street level with parking levels below the street, less experienced plow operators may not even realize they on a structure. For these decks, weight capacity signage and height barriers to prohibit large vehicles are appropriate.
Snow-related collapses can also occur in structures that are already weakened by significant deterioration. In rare instances, a big blizzard is followed by heavy rains that make the once-light snow suddenly become heavy.
Less of a headline but a much more common for owners is damage done to parking structures by overweight snow removal equipment, causing roof damage leading to early deterioration and unexpected repair costs.
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