Quick Answer
Snow accumulation exceeding 6-8 inches is typically considered hazardous for roofs, especially those with flat or steep slopes, as it increases the risk of collapse or structural damage.
Roof Snow Load Assessment
When assessing the danger of snow accumulation on a roof, consider the roof’s pitch, material, and structure. A general rule of thumb is that roofs with a slope of 4:12 or steeper can typically support up to 20 pounds per square foot (psf) of snow. For roofs with a slope of 3:12 or less, the safe load drops to 15 psf.
Measuring Snow Load
To determine the actual snow load, multiply the roof’s square footage by the expected snow accumulation and then by the weight per square foot (psf) of the snow. A 1-inch snowfall typically weighs around 5 pounds per square foot. For example, if a 1,000 square foot roof has 8 inches of snow accumulation, the load would be: 1,000 sq ft x 0.67 ft (8 in / 12 in) x 5 lbs/sq ft = 3,350 pounds or approximately 16.75 psf.
Mitigating Snow-Related Risks
During heavy snowfall, inspect your roof regularly for signs of strain or damage. Consider clearing snow from the roof if you have the necessary equipment and expertise. Ensure adequate ventilation in your attic to prevent ice dams from forming and reduce the risk of water damage. In extreme cases, consider installing a roof snow load monitoring system to detect potentially hazardous conditions.
Find more answers
Browse the full Q&A library by topic, or jump back to the topic this question belongs to.