It’s officially winter and snow is imminent. The snow that collects on your roof can cause damage if it gets too heavy, and possibly leaks if there are holes if your roof or framing. Collapse is more common in areas that experience yearly heavy snowfall and occurs because of damage and/or poor design and construction. While collapse because of snow is a concern, it is not a guarantee during heavy snow. Still, it is a common enough that homeowners need to be aware of the possibility.
According to FEMA, fresh snow can weigh as little as three pounds per square foot compared with 21 pounds for wet, heavy snow. Ice weighs more at 57 pounds a square foot. The average-size roof in the United States is in the range of 2,000 square feet; the weight of ice and snow can add up fast. Structures built before 1975 are more susceptible to collapse because of lack of building codes.
The risk of collapse is much higher for flat roofs. Flat roofs, while becoming popular for residential structures, are more prone to collapse from the weight of snow than a sloped or pitched roof. Flat roofs do not disperse weight like sloped roofs. The steeper your roof angle the more snow it can hold. These roofs rarely collect as much snow. Snow slides off of a pitched roof, or get blown off by the wind. A flat roof or shallow-pitched roof will almost always collect more snow.
Flat roofs are more dangerous and commercial buildings with flat roofs are usually the ones to collapse. If the drainage system freezes on a flat roof or needs cleaning, the melted snow will sit on the roof and add extra weight. The wind also does not help in removing snow from a flat roof as it will blow to another part of the roof. Up to 1-2 feet of snow on a flat roof can cause a collapse.
Along with the structural design of your roof, materials are a key factor in the possibility of a collapse. Slate or asphalt shingles are the best roofing materials for supporting the weight of snow. Metal roofs are also a great option for areas with high snowfall as snow will slide off.
If you notice leaks either on the interior or exterior of your home, mold/mildew, termites, missing shingles, or gutter damage, you roof needs an inspection and is at risk of collapse in heavy snowfall.
When a roof collapses because of snow, there is no single reason that led to the collapse. Most roof collapses result from the following:
- Poor design
- Poor construction
- Lack of maintenance
- Structures built prior to building code requirements
- Insulated roofs of older structures that prevent heat from melting snow
- Any combination of these factors
To answer the question “will snow collapse my roof?”, there is no definite answer. The amount of snow accumulation on one roof would be fine on another. If you suspect your roof might collapse under the weight of heavy snow, have a professional inspection.