Looking at my roof this morning, I thought, "How much snow can it take before it starts doing damage?" This "article from Ask the Builder" goes a long way in answering that question. According to the article, the typical roof is designed to accommodate 20 pounds per horizontal square foot. How much snow that is depends on the type of snow. Wet, heavy snow obviously weighs more than the powdery, dry stuff, and ice weighs the most of all. As a general rule, if your roof has over a foot of wet, heavy snow then you are pushing the limit of your roof. Ice is about three times as heavy as wet snow, so only four inches of ice on your roof is trouble. Steep roofs can be cleared by homeowners using a snow roof rake. If you are unable to clear the snow from your roof safely by yourself, call a professional and make sure that pro has Workman's Compensation and liability insurance. You don't want to be on the hook if they injure themselves while working on your home.