How Much Weight of Snow Can Your Roof Handle?
One of our carriers mentioned this topic the other day on LinkedIn and it got us thinking. Do our clients understand how much weight their roofs can hold? This will be very important in the winter months if we get heavy snow. Understanding how much weight (snow) your roof can handle can decrease the risk of damages and having to file a homeowner’s insurance claim. While it sounds like it would be a very difficult and mathematical task, don’t stress out yet, because it’s very easy to determine. Ok, so here we go. First, every roof is designed to handle about 20 lbs/square inch. Now, we must understand how to calculate how much snow is on the roof to determine how much weight is on it. The density of snow is important here. However, a rough guess will do. Here are the densities of snow and you can determine which one you think is most likely to be on your roof.
Fresh snow: 3.75lbs/cubic foot
Damp, fresh snow: 6.87lbs/cubic foot
Settled snow: 15.61lbs/cubic foot
Wind-packed snow: 23.41lbs/cubic foot
Very wet snow: 46.82lbs/cubic foot
Pure ice: 57.25lbs/cubic foot
Now you multiply the density of snow (lbs/cubic foot) by the depth (in feet). Now, this would be calculated for a completely flat roof which most of us don’t have. You will have to calculate it with the angle or pitch of the roof. Most are roughly between 14 degrees to 36 degrees. Ok, that’s it. Here is the formula to calculate:
snow load = thickness x density (resulting units will be in lbs/ft squared
snow weight: length of roof x width of roof/cos(pitch angle) x snow load
Let’s look at an example. Let’s say your roof has an angled slope of 17 degrees. The length of your roof is 20ft across. The width is 30ft. It has snowed 2ft of snow overnight so the snow is probably settled a bit and will have a density of 15.6lbs/cubic foot. Let’s plug these values in to see if the roof can handle the weight of that snowfall. This home would not hold that snow load and would collapse to cause damage. And just like that, you know how to calculate the snow load on your roof. However, if you don’t like doing these calculations, this website will do them for you. Let’s hope that this winter is another mild one and we don’t even have to worry about this this year ;)