Winter's beauty often comes with a hidden burden: snow. While a snow-covered roof might look picturesque, it can also pose a serious threat to your building's structural integrity. Understanding roof snow load is crucial for ensuring the safety of your building and its occupants.

Many people mistakenly believe that simply eyeballing the snow depth is enough to gauge the risk. However, this is a dangerous misconception, especially in a changing climate . Relying solely on snow height is like judging a book by its cover—you're missing the full story.

This article will delve into five essential aspects of roof snow load, debunking common myths and empowering you with the knowledge to make informed decisions about winter roof management.

With respect to climate change, the question arises as to whether the risks relating to snow loads will increase. The future probability of a continuous snow cover occurrence with frequent freezing/thawing cycles will probably decline due to predicted higher temperatures. However, where temperatures remain low, an increase in winter precipitation will result in increased snow loads. Furthermore, the variability of extremes is predicted to increase. If heavy snowfall events are more frequent, the risk of a trigger event will likely increase.

Snow loads in a changing climate: new risks?, Nat. Hazards Earth Syst. Sci. 2008. Ulrich Strasser, PhD

What is Roof Snow Load?

Roof snow load refers to the downward force exerted on your roof by the weight of accumulated snow and ice. It's a critical factor in structural engineering, as excessive snow load can lead to:

• Roof Collapse: In severe cases, the weight of the snow can exceed the roof's capacity, causing it to buckle or collapse entirely. Imagine the devastating consequences of a roof collapsing under the weight of snow, potentially injuring occupants, damaging property, and disrupting business operations.

• Structural Damage: Even if the roof doesn't collapse, heavy snow load can cause structural damage, such as sagging rafters, cracked ceilings, and damaged walls. These issues may not be immediately apparent but can weaken the building over time, leading to costly repairs and potential safety hazards.

• Leaks: Snow and ice can melt and refreeze, creating ice dams that prevent proper drainage, leading to water infiltration and leaks. Water damage can lead to mold growth, rot, and further structural deterioration, compromising the building's integrity and posing health risks to occupants.

Why Snow Height Isn't Enough

While snow depth is a factor in determining snow load, it's not the whole picture. Here's why:

Snow Density Varies

Snow can be light and fluffy or dense and wet, depending on temperature, humidity, and other weather conditions. A foot of fresh, powdery snow weighs significantly less than a foot of compacted, wet snow. For example, a cubic foot of fresh powder snow might weigh around 7 pounds, while the same volume of wet, packed snow could weigh up to 20 pounds. This means that two roofs with the same snow depth could have vastly different snow loads.

Can you really tell the difference just by looking?

Hidden Layers

A seemingly shallow layer of snow might conceal heavier layers of ice or compacted snow beneath, making visual estimations unreliable. For instance, rain falling on snow can seep through the snowpack and freeze, creating a hidden layer of ice that significantly increases the weight without changing the visible snow depth.

Uneven Distribution

Wind can create uneven snowdrifts, concentrating heavy loads on specific areas of the roof, even if the overall snow depth appears manageable. This is particularly common on roofs with complex shapes, multiple levels, or obstructions that can trap snow, like mechanical units. These drifts can create concentrated stress points, exceeding the capacity of certain roof sections even if the average snow load is within acceptable limits.

Factors Affecting Roof Snow Load

Understanding the factors that influence snow load is essential for accurate assessment and effective roof management:

Geographic Location

Areas that receive heavier snowfall naturally have higher ground snow loads, which directly impact roof snow load calculations. Building codes, such as the National Building Code, take geographic location into account when specifying snow load requirements for building design. For example, the National Building Code assigns higher snow load values to regions with historically heavy snowfall, like coastal areas or mountainous regions.

Roof Shape and Pitch

Steeper roofs shed snow more easily than flat or low-sloped roofs, reducing the snow load. However, complex roof geometries can create areas prone to snowdrifts, increasing the load in those spots. The National Building Code provides guidelines for calculating snow loads based on roof slope and shape, taking into account factors like valleys, dormers, and other architectural features that can influence snow accumulation.

Roof Surface

Smooth surfaces, like metal roofing, allow snow to slide off more easily than rough surfaces, like asphalt shingles. This is why metal roofs are often preferred in areas with heavy snowfall, as they naturally reduce the snow load and minimize the risk of ice dams.

Building Heat

Heat escaping from a building can melt snow on the roof, which can then refreeze, forming heavier ice layers. This is a common problem with poorly insulated roofs, where heat loss through the roof deck can create a cycle of melting and refreezing, leading to a buildup of ice and increased snow load.

Wind

Wind can blow snow off the roof, reducing the load, but it can also create drifts, concentrating heavy loads in specific areas, like around mechanical units. The National Building Code includes factors for wind exposure and drifting snow in its snow load calculations, recognizing that wind can significantly alter snow distribution and create localized areas of high stress.

Previous Snowfall

Multiple snowfalls, especially if the snow doesn't have time to melt between storms, can lead to denser, heavier snowpack. This is because the weight of new snow compresses the existing snowpack, increasing its density and overall weight.

Rain or Sleet

Rain or sleet falling on snow can significantly increase its weight and density, putting additional stress on the roof. This is a major concern in areas with fluctuating winter temperatures, especially now with climate changes , as a layer of rain or sleet can quickly transform a light snow load into a potentially dangerous burden.

In general, higher temperatures will result in a reduction of snowfall and an increase in rainfall. Rain falling however on snow, can be stored within the snow pack resulting in an increase in the total snow load.

Snow loads in a changing climate: new risks?, Nat. Hazards Earth Syst. Sci. 2008. Ulrich Strasser, PhD

The Importance of Professional Inspections

While you can take some steps to assess your roof visually, it's crucial to have a professional roof inspection , especially:

• Before Winter: A pre-winter inspection can identify potential problems and ensure your roof is ready for the challenges of snow and ice. This includes checking for loose or damaged shingles, flashing, and gutters, as well as assessing the overall condition of the roof structure.

• After Major Snowstorms: Heavy snowfall can cause damage or create hazardous conditions. A professional inspection can assess the roof's condition and recommend necessary actions, such as snow removal or repairs.

• For Older Buildings: Older buildings, especially those with flat roofs or known structural issues, are more vulnerable to snow load damage. One of the reasons is that load thresholds in the National Building Code are based on the last 50 years of data, and that they weren't built to sustain the new risks of our changing climate . Regular inspections are essential to monitor their condition and address potential problems before they become serious.

Professional inspectors have the expertise and equipment to accurately assess snow load and identify potential hazards. They can also advise on appropriate snow removal strategies and recommend necessary repairs.

The Power of Smart Roof Monitoring

Technology is transforming roof management, offering a more proactive and efficient approach to snow load monitoring. Smart roof monitoring systems , like Domely Connect, use a combination of sensors, cameras, and AI to:

• Continuously Monitor Snow Load: Sensors provide real-time data on snow depth, density, and water equivalent, eliminating the need for manual measurements and guesswork. This allows for constant awareness of the snow load on the roof, even during storms or when the building is unoccupied.

• Detect Potential Problems: AI-powered visual inspections analyze daily images of the roof, identifying issues like ponding water, clogged drains, and ice. This early detection allows for timely intervention, preventing minor problems from becoming major headaches.

• Send Proactive Alerts: The system automatically sends alerts when snow load approaches critical thresholds or when potential problems are detected, enabling timely intervention. This gives building managers ample time to schedule snow removal or repairs, minimizing the risk of damage or safety hazards.

By leveraging smart roof monitoring , you can gain peace of mind knowing that your roof is under constant surveillance, allowing you to make data-driven decisions and prevent costly damage or safety hazards.

Beyond Guesswork

Roof snow load is a complex issue, and relying on visual estimations alone is a risky gamble. By understanding the factors that influence snow load, scheduling professional inspections , and embracing smart monitoring technologies , you can take a proactive approach to roof management, ensuring the safety and longevity of your building.

Stop guessing and start knowing. Contact Domely today to learn more about how smart roof monitoring can revolutionize your winter roof management strategy.