Extra Space in Your Community

With all the snow we’ve had lately, and more on the way, I started to think about the roof. Ever since the roof of the Iron Horse Inn in Durango collapsed two weeks ago, I’ve been worried. I haven’t seen any stories in the news about self-storage roofs collapsing. But still–could it happen here? I decided to find out. Here’s what I learned:

• Besides the weather, there are several factors that affect the risk of a snow-related roof collapse at a self-storage building (or any building). The first factor is the age of the building and whether or not it was designed to withstand the weight of a heavy snowfall. Since the self-storage industry is relatively new, most self-storage buildings are built to the newest codes–the ones that require roofs to sustain the greatest amount of weight. Buildings built before 1991 are at greater risk–the codes didn’t require such strong roofs back then.
• To put it another way, every building or structure was designed to withstand a certain amount of snow or rain weight. In the mid-Atlantic states, where so many roofs are collapsing lately, roofs are mostly designed to withstand 10-20 pounds of snow weight per square foot of roof. In snowier areas (like here), most roofs are designed better for snow and can withstand more like 40 to 70 pounds of snow per square foot.
• I wondered how I was supposed to weigh the snow on my roof. No problem: it turns out there is a formula. For fresh snow, 10-12″ = 1′ water = about 5 pounds per square foot (psf) of weight on the roof. No problem there. For packed snow, 3-5″ of old snow = 1″ water = again, about 5 psf. Still no problem. Another formula is that ice is much heavier — an inch of ice = about a foot of fresh snow, or another 5 psf. No problem by itself.  But if you have two feet of old snow and two feet of fresh snow, on top of an inch or two of ice, then you’re talking about 20-30 pounds right there, with more snow on the way. Worse yet, if it rains on top of your snow, the snow will soak up the rain like a sponge, increasing the weight exponentially (Cheryl Rotole, from www.RoofRake.com, told me that).
• Another factor is the features of the roof. Roofs with any kind of protuberance have an area of greater risk where the snow drifts next to the protuberance, whatever it is. Then there is the slope of the roof. There is much less risk of roof collapse if the snow is sliding off the roof regularly–but in some cases, you have to watch where that snow is sliding. You don’t want heavy snow or icicles falling on passers-by or damaging vehicles. Self-storage roofs tend to have some rise to them–they aren’t as flat as they look–and, they’re built to code for the areas where they are located–so they have more rise to the roofs if building codes demanded it.
• The buildings with collapsed roofs have tended to be large, like the Iron House Inn, or the storage building at the Smithsonian that recently collapsed. That’s because the weight of the snow will find the roof’s weakest point — the point where it has the least support. That’s at the center. The larger the roof, the larger the unsupported area. The smaller the roof, the closer most of the roof is to walls that can help to hold whatever weight might be pressing down on it. Maybe that’s another reason why we haven’t heard much about smaller self-storage buildings collapsing — and instead the news is full of high school gyms and conference centers with roofs that have given way.

You might think that’s all there is to know about roofs and snow–but it isn’t. More tomorrow…meanwhile, be safe out there. Go check your roof, and if it looks like you have too much snow, find a way to remove it without climbing up there yourself–you don’t want to add your own weight to the weight of the snow.