S = CbSS + Sr
This is the snow-load equation for typical home construction, according to the National Building Code. Chances are you won’t need to know how to solve this equation, but you should be aware of the basics of your roof’s limits.
If you’re concerned about the weight of snowfall on a roof, particularly an older one, Cathy Taraschuk, senior technical advisor, structural and earthquake design, at the National Research Council, says there will be signs of stress: “These can include unusual sounds from the roof or supporting walls, visible movement of walls or deflection of [structural] members, and cracking of drywall or plaster.”
Taraschuk warns that you should never clear a roof yourself; instead, you should opt for a qualified and insured company. Although you can reduce some load by using a snow rake to pull the snow off the roof safely from ground level.
Also, keep shed roofs in mind. Taraschuk says you should check with your local building authority to see if there is a building code for a small structure that is less than 10 square metres in area with no plumbing. If you do opt to pull out your calculator and use the formula, remember the answer will be different, as temperatures and precipitation vary by region.