Extreme cold weather such as the 2019 polar vortex event poses many threats. The main risk for humans, animals and plants is the low temperature, especially when combined with fast wind. However, property can also be damaged by cold weather, and sloped roofs with poor insulation are especially vulnerable to ice accumulation.

When snow builds up on a rooftop, there are two main problems: the increasing weight as more snow accumulates, and the water produced when it melts. When ice is allowed to form, large pieces may break off and fall - this represents a hazard for individuals, vehicles and surrounding properties.


Make sure your building is well designed for cold weather.

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Preventing Snow and Ice Accumulation on Sloped Roofs

When snow is allowed to accumulate on a sloped roof, it tends to form a barrier of ice around the roof edges. This formation is called an ice dam, and it leads to the accumulation of more snow and ice. Normally, an ice dam is formed through the following process:

  • Indoor heat accumulates under the roof, especially at the ridge - the highest point of the slope.

  • Roof temperature around the ridge increases above the freezing point of water (32°F), melting the snow.

  • Water flows downward, but lower roof areas and edges are still below 32°F.

  • Before water can reach the drainage system or gutters, it freezes again and forms the ice dam.

Ironically, the ice dam is a consequence of indoor heat escaping through the rooftop. If the roof temperature can become more uniform, so that all the snow melts at once, ice dams cannot form. Cleaning the snow to prevent its accumulation is also useful, but this is a dangerous task for untrained personnel - you should get in touch with a qualified contractor.

Adequate roof insulation and airtightness are the most effective measures to mitigate the formation of ice dams. By keeping heat inside the building, insulation leads to a more uniform roof temperature. This prevents the uneven temperature distribution that causes snow to melt around the ridge and freeze again around the edges.

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In addition to preventing ice dams, a well insulated roof keeps more building heat inside, reducing the workload on your space heating systems. Regardless of the energy source used - heating oil, natural gas or electricity - your utility bills are reduced with proper insulation.

Water accumulated behind an ice dam can bring additional problems if allowed to leak inside your property. Moisture can damage many construction materials, and it can stimulate the formation of mold. In both cases, the required reparations are normally very expensive.

Can Your Building’s Roof Structure Withstand the Weight of Snow?

Snow may not seem heavy when you grab a small clump, but it can add several tons of load when it accumulates on a large roof. The weight of snow varies according to its composition, but for a quick calculation you can assume that 1” of snow adds one pound per square foot. For a commercial rooftop with area of 10,000 sq.ft. and 4” of snow accumulated, the estimated load is 40,000 pounds (20 tons).

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If your property is designed and built according to the latest construction codes, snow loading should not be an issue because it is factored in code requirements. However, older roofs may be vulnerable, especially in winters with record levels of snowfall. To make sure your roof can withstand the expected snowfall for your location, the best recommendation is getting a professional assessment.

Does Building Insurance Cover Snow and Ice Damage?

Insurance plans are an effective safeguard against property damage, but consider that coverage may not apply for damage that is considered preventable. Since there are ways to mitigate snow and ice damage, your insurance plan may not apply, forcing you to assume the full cost of reparations. Consider that ice and snow damage can extend beyond the roof itself; your building interior may be damaged if there are water leaks, and falling ice chunks can affect third parties.

If you have a sloped roof, the best recommendation is preventing ice and snow damage with adequate insulation. In addition, this will reduce your heating bills while improving safety for neighbors and pedestrians. To clear doubts about the structural condition of a roof, the best recommendation we can give is a professional inspection.

 

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