In regions that receive a lot of snowfall, choosing the right roofing material is important. Snow can cause damage because of its weight and temperature. It also can cause damage on a roof as it melts and drips off. You can avoid or mitigate the effects of this damage with proper planning.
The pitch or steepness of the roof is important to help you decide between metal or asphalt shingles. A low pitch asphalt shingle roof that is 3:12 (3 inches rise in 12 inches of horizontal) or less often cannot be warrantied by roofing contractors or material suppliers. Snow depth could build up too much over the winter, producing too much weight and load on the roof, causing potential for collapse. Higher pitch roofs are better for asphalt shingles because the snow can roll off the roof. Snow will slide off of a lower pitched metal roof more easily.
Snow sliding off of metal roofs has the potential to cause harm or damage. If you are designing a house, you can avoid this by not sloping a roof over doorways, decks or walkways or design lower shed roofs that will send the snow in alternate directions. If it's unavoidable or the building is existing and has these conditions, you can install snow clips or snow guards on the roof. They are put on the lower few feet of the eaves and they hold the snow on the slippery roof until the snow can melt. Some people may not like the aesthetics of a sleek roof being cluttered, however. Snow drags more on asphalt shingles and does not have as much tendency to slide.
Ice dams happen when snow melts a bit, but then the water doesn't have a chance to drain off the roof before the sun sets, the temperature drops and the water freezes on the roof. As this happens over a few consecutive days, the ice builds up dangerous weights on the roof, and creates equally dangerous icicles that can drop on people below. Eaves are where this happens the most because they are closer to the exterior walls where there is usually more heat. The best solution is keeping the roof colder with better insulation and ventilation, but metal roofs also drain more easily and quickly.
Asphalt shingles tend to be less expensive than metal roofing; however, metal roofing has a longer lifespan. Asphalt shingles are sold with 15- to 30-year warranties, but metal roofing warranties start at 30 years. There is less maintenance for metal as well, which may make the lifetime cost of metal less. Robust materials will also last longer during the many snow seasons. Asphalt shingles will degrade more over time with the severe weather.