As the age of winter approaches, the outside world becomes the enchanting world of Narnia. Although everything is so beautiful and mesmerizing, the snow brings its own problems. Don’t panic; there is no white witch in real life, but the heap of snow over your head is something to worry about. Moreover, unexpected snowstorms, ice dams, and snow piles can cause your roof to weaken, leak or even collapse.
But you hired the best structural engineer to build your roof, and it’s been only a few years. Regardless of your house’s age, too much snowfall poses dangerous risks that can cause an unexpected tragedy.
How much snow load can your roof bear? What’s the best roof design for snow load?
Let’s jump right into the details.
How much snow can a roof hold?
According to Insurance Institute for Business & Home Safety, most residential roofs can withstand 20 pounds per square foot of snow. We will talk about how to measure the snow on your roof, but what’s important here is that you should be extra vigilant when it comes to roofs in winter.
The uneven distribution of snow, rain-on-snow load, snowmelt between snow events can weaken your roof. Moreover, the numbers can vary depending upon your roof’s age, shape, maintenance, construction, and slope.
Houses built before 1975 are more susceptible to collapsing. If your house has a flat or low slope roof, snow will accumulate more quickly, hence posing a greater risk.
IBHS suggests that the best roof design for maximum snow load are steep roofs with slopes greater than 3 inches of slope in 12 inches of horizontal distance. They allow snow to melt off more quickly—reducing the overall stress on your roof.
How much the snow on your roof weighs?
The actual weight of the snow depends on its water content. Typically, the water content ranges from 5% to 32%, with 20% being the average value.
Confused about this whole water content thing? Simply put, the water content tells us the snow-to-liquid ratio.
With that out of the way, what is the snow weight per square foot on your roof?
A simple rule of thumb (for an average pounds per square foot) would be to multiply the inches of snow on your roof by the square footage of your roof. But depending on the type of snow, the numbers vary drastically.
Suppose you have an average-sized 1,500-square-foot roof with 12″ of snow; here’s how you can calculate the roof load from snow:
Fluffy snow (15:1)
This is the snow that’s relatively easy to shovel. So, in our case, the snow weight per square foot on the roof is 4.1 lbs./sq. Ft. This equals 6,240 pounds of weight on the roof.
That’s equivalent to a class 1 pickup truck on your roof.
Normal/Fresh Snow (10:1 to 12:1)
Typically, the snow-to-liquid ratio for normal snow ranges from 10:1 to 12:1, meaning that a foot of snow weighs about 5-6.2 pounds per square foot.
For a 1,500-square-foot roof, there will be approximately 9,300 lbs. weight on the roof.
Wet/Packed Snow (3:1 to 5:1)
You don’t want the weight of three pickups above you, right?
For wet snow, there’s about 12.5 lbs./sq. Ft. on your roof. So, in our case, the weight goes up to 18,700 lbs.
But still, it is less than 20 lbs./sq. Ft. What if we double the snow to 24″?
The snow weight per square foot reaches up to 25 lbs./sq. Ft — that’s six pickup trucks on your roof.
What happens if you don’t get rid of the extra snow? Suppose there are another 2 feet of new snow on top of the 2 feet old snow. It will weigh 60 pounds per square foot of roof space.
One inch of ice equals one foot of fresh snow.
What happens if there’s too much snow on the roof?
Wondering about how much snow is too much snow? Or what are the signs of a stressed roof?
Remove excess snow immediately if you observe any of the following signs:
- Icicles are formed when the snow melts and refreezes, forming an ice layer on the roof. The ice having more density causes a lot of extra stress on the roof.
- Head up to your attic and look for cracks, leaks, or any signs of overstressing.
- Look for sagging ceiling tiles, creaking or popping noises, or sprinkler line.
- If doors and windows feel jammed, the snow on your roof has exceeded its safe limit. This is because the entire house’s frame has deformed due to the excessive load on the roof.
So, if the snow load becomes dangerously high, get help from a professional as dealing with the roof snow alone is not recommended.
If you still want to do it, use a long pole or snow rake with a long extension arm to pull the top layers of the snow down while wearing a roof fall arrest harness. Don’t forget the icicles!
To protect your house and family, you must remove the extra snow off your roof. Although different regions produce different types of snow, it’s crucial that you’re aware of how much load your roof can bear.
Moreover, excessive rainfall, a constant thaw-and-freeze cycle, or an unexpected snowstorm can increase the snow load drastically in a matter of hours.
So, if you observe leaks and cracks in the roof, immediately evacuate the house and contact a professional contractor to remove the snow and ice for you.