Do I Need to Worry About Snow Weight on My Roof?
- When constructed properly, all buildings are designed to withstand a certain amount of weight from snow, ice and debris. Commercial and residential buildings are required to withstand a certain amount of snow load, which varies by area. In southern regions with little snowfall, residential roofs may be designed to hold 5 to 10 lbs. of snow. In northeastern areas where snow is heavier, buildings may hold up to 40 lbs. of snow weight. If you live in a modern home (built in the last 50 years or so) that has been properly built, your roof is already designed to withstand normal snow weight. When snow is excessive and extremely wet, it may put an unexpected weight burden on your roof.
- All roofs are not created equally. Homes built with substandard materials and homes that have been poorly maintained may have weak roofs that cannot support even ordinary snow weight. Look for signs that snow weight is too much by looking at the roof, walls, doors and supports of the building. If the doors and windows begin to look bowed or warped, snow is putting too much weight on the roof. Cracked beams and visibly sagging areas of the roof are warning signs that you have a serious problem. Speak to a building inspector or professional from the fire department is you notice these signs.
- A little sagging and bowing under snow weight may not be permanently damaging if the integrity of the roof remains intact. In these cases, the roof will return to normal once snow weight is removed or naturally melted. Once beams and walls begin to give into the pressure and crack or break, the sagging will be permanent. When the actual weight of the snow far exceeds the amount of pressure the roof is designed to withstand, total collapse is a possibility. Be especially mindful of snow buildup on large roof overhangs that have little to no underside support, multilevel roofs where large piles of snow tend to accumulate in one area and roof valleys or nooks where snow and ice collect while falling and melting.
- Total roof collapse is unlikely, but it is a possibility. Snow can create permanent damage to the roof, but removing snow can be damaging as well. Cold shingles can be damaged or destroyed when snow is being forcibly removed, and it's extremely dangerous to attempt to remove snow from a roof. Falling snow and ice can create injury to surrounding people and items nearby. One inch of water or snow weighs about 5 lbs. per square foot. Do the math when snow falls. A roof made to support 20 lbs. of weight can withstand up to 12 inches of very watery, heavy snow. Blueprints will show the amount of weight the roof of the building is designed to hold.
