Calculate Roof Snow Load (PSF)
Calculate snow weight on your roof by depth and snow type. Know when to clear snow to prevent collapse.
Understanding Roof Snow Load
Snow weight varies dramatically by type: fresh powder weighs 3 lbs per cubic foot, but packed snow weighs 15 lbs and ice 30 lbs. An 18-inch layer of settled snow creates 15 PSF (pounds per square foot) of load. Most residential roofs are designed for 20-40 PSF depending on region. When snow load approaches your roof's design capacity, it is time to remove snow.
When to Remove Snow
Warning signs: Interior doors suddenly sticking, visible sagging in roof or ceiling, cracking sounds from the roof structure, water leaking at wall-ceiling joints. General rule: Remove snow when depth exceeds 2 feet of packed snow or 4 feet of powder. Use a roof rake from the ground — never climb on a snow-loaded roof.
The most dangerous time for roof collapse is not during the snowstorm — it is 2-3 days after, when warm temperatures partially melt snow into dense, heavy slush. Snow that seemed manageable at 15 PSF can become 25+ PSF as it compacts and absorbs meltwater.
