When storms generate lots of snow – especially the wet, heavy variety – you want to make sure your home is able to withstand it. This also includes being able to hold all of the weight of the snow on your roof. An excessive amount of snow on could put your home and your family in danger if it is not taken care of. This is situation is often termed as Snow Loading, which is the downward force exerted on structures by the weight of accumulated snow.
Snow loading is dictated by many factors influencing snow and ice accumulation on the structure, and varies considerably by geographic location.
In this case, the heavy snow that tends to fall on Minnesota roofs may not fall off like it is supposed to and considering the fact that the ice layer tends not to melt until spring each additional snowfall tends to intensify the problem. And it’s worth pointing out, that just because a roof has endured many winters of heavy snow does not mean it will last indefinitely.
Snow loads for buildings in the south and west of Minnesota are usually about 20 pounds per square foot. Majority of roofs are designed for a “total” general load of 25 to 30 pounds per square foot. This assumes that the building was properly designed by a registered Professional Engineer (PE), and constructed by a qualified builder according to the design.
So, the question we should ask is, how much weight can/should most roofs in Minnesota take? While there are no clear guidelines on how much snow is too much for a roof and it definitely depends on the home and roof design.
In Minnesota, the state’s building code requires homes in the southern half of Minnesota to have roofs that can support at least 35 pounds per square foot while in northern Minnesota, the requirement increases to 42 pounds per square foot. To be more specific, if the building code is 35 pounds per square foot, your roof should be able to support 7 feet of fresh snow; 2.5 feet of packed snow; 7 inches of ice, 1.75 feet of wet and heavy snow. Anything beyond and above those totals will begin to stress your roof.
It’s common knowledge that cold fluffy snow doesn’t weigh much, while wet snow can be extremely heavy. Also, you must keep in mind that as the snow sits there, it compacts, so even if the snow was initially light and fluffy, the longer it’s on your roof, the heavier it gets. Additionally, melting snow can turn to ice if that snow melt doesn’t run off the roof. Which inevitably adds on to the weight? As a result, this leads to further deterioration of the roof and its holding ability.
So, what is a reasonable amount of snow that a Minnesota roof can handle over a long period? Well, to give you an idea of what a mass of snow weighs, 5 pounds per square feet of snow would equal 19 inches of light snow, almost 3 inches of heavy, wet snow, and 1 inch of water or 1 inch of ice. The amounts continue to go up with the amount of weight, bringing a half foot to a foot or more of snow causing problems on a roof. Overall, a safe bet would be about half of the roof’s designed load or about two feet of snow or one inch of ice and one foot of snow.
However, there are several factors that tend to affect how much snow builds up on roofs. For example, shingled roofs aren’t known to be good shedders of snow compared to metal roofs. Another case is, poor roof pitching, which doesn’t allow for snow to slide off properly.
On the other hand, “Lean-tos” is where the roofs on lower buildings end up collecting snow or ice sliding off a higher roof. Additionally, Snow drifts – which is wind blowing snow onto other buildings leading to uneven snow loads on roofs. Also, in some cases there may be roof valleys – parts of the roof that compound snow more.
So what should you do if, you have too much snow on your roof? The simple answer is to remove it as soon as possible. Generally there is some time between a large snowfall collection and the roof’s structural collapse.
Plus, if you have a properly constructed sloped roof, there shouldn’t be much worry about structural collapse because it won’t be as deep as snow on the ground.
It’s better to go for a long-term solution that prevents or severely cuts down on the amount of snow that can build up on a roof. An example of an innovative solution would be increasing the buildings temperature using large heaters to melt the ice layer, forcing the compounded snow and ice to melt off eventually. On the other hand, you can simply contact a snow removal company or do it yourself and begin removing the snow from your roof to prevent a possible collapse.