Snow while a beautiful part of winter can cause damage and even collapse your home’s roof. Collapse from snow can cause thousands in repairs or result in fatalities. In this post we will cover how much snow a roof can hold, how to evaluate your roof’s limit for weight, signs of excessive snow build up, and safe snow removal.
How Much Snow Can a Roof Hold?
According to the Insurance Institute for Business and Home Safety, most residential roofs in good condition can support 20 pounds per square foot of snow. To help you determine when the snow on your roof may be approaching this weight limit, use these guidelines:
- Freshly Fallen Snow: Around four feet of fresh snow equals 20 pounds per square foot.
- Old, Packed Snow: Around two feet of old, packed down snow equals 20 pounds per square foot.
- Mixed New and Old Snow: Around two to three feet of both new and old now equals 20 pounds per square foot.
Evaluate your risk of roof-top snow/ice accumulation
- Snow usually melts off of steep sloped roofs (slopes greater than 3 inches of slope in 12 inches of horizontal distance) more quickly than flatter roofs.
- Know the lower sloped areas and flatter roofs of your home. Ice and snow will typically accumulate more quickly on low slope and flat roofs.1
Estimate How much Weight your Roof Can Support
- House roofs should support 20 lbs./square foot of snow before they become stressed.
- Local building codes dictate the snow load required for residential roofs. Contact your local building code department to determine the snow load requirements for your area.2
Key Factors: Weight and Water Content
- The water content of any given cubic foot of snow can strongly influence how much the snow actually weighs.
- A rule of thumb – regarding the weight of average snow: One inch of snow, on average, weighs 1 lb. per square foot. That knowledge is what tells you that mere 1.75 inches of average-weight snow on a typical roof is the equivalent of one compact SUV parked on the roof.
- A rule of thumb regarding the weight of light, fluffy snow: One inch of snow weighs 0.26 pounds per square foot. That means for every 6.5 inches of snowfall you’ve got the weight of a compact SUV on your roof.
- A rule of thumb regarding the weight of heavy, wet snow: One inch of snow weighs 1.66 pounds per square foot. That means that for every single inch of heavy, wet snow on an average-sized roof, you’ve got the equivalent of one compact SUV parked up there.
- Older roofs may not be able to withstand as much snow as some of the guidelines listed above.
- Flat roofs hold the least amount of weight, depending on their construction.
- If you have an older roof, live in a manufactured home, or have a property with a flat roof, then it pays to be even more conservative: use 12 inches as your hard limit for snow removal.
- If you find it difficult to open any of your doors or windows this is a sign the snow load has grown too heavy for your house to bear. Seek the help of an ice and snow removal service immediately.
Signs of Roof Damage from Excessive Snow
These are some signs to look for that your roof has too much weight from snow:
- Doors that pop open for no reason
- Windows that are hard to open or close
- Numerous cracks in wall or masonry
- Major roof leaks that cannot be linked to an identifiable cause
- Frequent creaking, cracking, or popping sounds
- Visible sagging roof
How Do I Safely Remove Snow?
Always stand on the ground when removing snow, never stand on a ladder! Use a roof rake with rollers or a plastic edge to pull the snow off your roof. Use a rake with an extendable pole so you can stand far enough away from the edge of the roof. Never climb onto your roof to remove snow you risk seriously injuring yourself. It’s always safest to hire a professional if you feel you can’t safely do it yourself.