In winter, in North America, snow is something we know well. And while it makes landscapes beautiful, it can also pose a real risk of roof collapse—especially when roofs are aging, poorly maintained, or built with construction or design defects. To better understand the risks and best practices for monitoring roofs, we spoke with Antony Beaulieu, civil engineering expert at Origin Enquêtes technico-légales inc., a firm specializing in post-disaster forensic engineering.
The construction code considers smooth surfaces such as metal, composite, or glass roofs slippery above a certain slope. Below that angle, they hold snow much like a flat roof. Shingle roofs can retain snow at fairly steep angles.
The most at-risk roofs are those located below an extension or an addition built within 5 meters. These lower roofs receive additional snow loads that were not considered in their original design. Antony explains: “In our work, we frequently see collapses in these accumulation areas because, during building extensions, it’s often overlooked to verify whether the lower roof’s structure is strong enough to support the new snow loads being placed on it.”
Wind flow also changes in these configurations, creating heavy snow drifts. Another key factor: the environment. “A house next to an open field or wind corridor will accumulate snow differently than a building in an urban area,” says Antony. A windy corridor tends to reduce roof snow accumulation. In contrast, a building wedged between two taller buildings in the city will likely accumulate more snow, significantly increasing risk.
In many investigations led by Origin, collapses were not caused by a sudden excess of snow, but rather by slow, invisible structural degradation. A long-term infiltration can weaken a single connection point, shifting loads to other components, eventually causing failure. Wet or compacted snow adds significant weight, exacerbating existing weaknesses and potentially leading to sagging…or collapse.
Several early signs may indicate sagging or a potential overload:
It’s important to differentiate warning signs from vulnerabilities that increase risk even without visible symptoms.
For example, a building with poor insulation, inadequate ventilation, a deteriorating roof membrane, or neglected maintenance may show no obvious signs. Yet, the weakened envelope can lead to structural problems in the medium term. Poor insulation or ventilation encourages ice formation, increasing loads and accelerating material degradation.
These are not signs of immediate danger, but they are indicators that your roof deserves closer attention. A roof weakened by years of humidity, thermal fluctuations, or infiltration may fail suddenly under a heavy snowfall, without warning.
Yes. The Quebec Construction Code specifies snow-load requirements depending on climate zone and building configuration. However, these standards rely on historical data.
“With climate change, codes will eventually shift from historical loads to future projections,” notes Antony.
The biggest enemy of structures? Not powder snow—but wet, heavy snow, often created by warm spells and rain. Water adds weight, and on flat roofs, it cannot drain. “Collapses often occur during warm spells when rain falls on existing snow”, adds Antony.
After a sagging or collapse, Origin conducts a full investigation to determine the cause. This includes evaluating snow load, material condition, maintenance history, past infiltrations, and any non-compliant structural renovations.
Antony explains: “Often, it’s a combination of factors: an old building, neglected maintenance, and one storm too many.”
One word comes up repeatedly from the expert: maintenance.
Even if new buildings designed to code don’t need frequent snow removal, older ones benefit greatly from it. Annual structural inspections are recommended, especially in attic spaces.
The use of smart sensors, such as Tensio’s snow-load sensors, allows for continuous monitoring. These tools help avoid unnecessary interventions or trigger the right action at the right moment.
According to Antony, not always. There are general safety obligations, but specific snow-removal requirements are less known: “Many owners act on instinct, not based on technical criteria.”
A striking example?
Old barns to which additions were built. If the original structure wasn’t reinforced, the new roof dumps additional snow onto the old one… Result: collapse.
“Modifying a building without reviewing the existing structure is a common mistake”, reveals Antony.
Roof monitoring is not optional, it’s a responsibility. With increasingly unpredictable winters, detection tools, regular maintenance, and awareness of early warning signs are essential to ensuring safety, durability, and cost control.
To learn more about Tensio’s snow-load sensors and request a product demo, click here!
And thank you to Antony Beaulieu and Origin Enquêtes technico-légales inc. for their collaboration!