Knowledge of roof snow load in Calgary is necessary to keep any building safe and sound. Calgary’s extreme snowfall and temperature variations can put a lot of pressure on roofs, particularly flat or low-pitched roofs.
According to Angel’s Roofing, a Calgary-based contractor, accurately determining snow load is crucial in avoiding the risk of structural damage, and in meeting local building codes. Property owners have a key opportunity to protect their investment by proactively addressing snow load concerns.
This method provides for a safe and durable roof all winter long.
What Is Roof Snow Load
Roof snow load is the downward force created by snow accumulating on a roof. In Canada, we usually just measure it in kg/m². This measurement takes into account the density and depth of snow, which can range widely based on variables like temperature and compaction.
It’s a key component to figuring out what the pressure a roof needs to carry, especially in areas that experience harsh winters.
In Calgary, the ground snow load is the basis for determining the roof snow load. It depends on the climate patterns of the region. Calgary’s cold winters and frequent heavy snowfall lead to higher ground snow loads than areas with milder climates.
The mean ground snow load for Calgary is between 1.5 and 3 kPa. You have to modify this number for wind, roof slope, and exposure to the sun.
The basic roof snow load factor is an important public safety aspect in building codes. This factor takes into account not just the weight of snow, but structural factors such as roof pitch and load distribution.
It’s important when designing to account for these loads so that no long-term damage or sagging occurs, or worse, a complete roof collapse.
Accurate snow load calculations mean that a building can withstand Calgary’s sometimes extreme winter conditions, protecting valuable structures and the people that occupy them.
Risks of Excessive Roof Snow Load
Excessive snow accumulation on a roof poses serious risks, mainly structural issues such as roof collapse. Calgary’s heavy snowfalls, sometimes more than 20-30 cm in a storm, can pose serious risks to roofs, particularly if the snow drifts and accumulates unevenly. Wind can also carry snow, leaving one side of the roof bare and producing drifts on the other side.
This places additional weight overload on localized areas and compromises the structure’s overall integrity. Older buildings and structures with low-slope roofs are especially at risk, underscoring the importance of proactive snow removal.
Roofing materials are also adversely impacted by the effects of heavy snow. Extended weight can also crack or warp shingles and create sagging or even punctures in flat roofs. As repairs for this type of damage can cost hundreds of thousands of dollars, preventative care becomes crucially important.
For example, a small crack in a shingle can appear harmless, but can let water in that will cause much worse issues eventually. Ice dams are a frequent problem when snow melts and refreezes at roof edges. These dams create drainage paths, making water back up underneath shingles, leading to leaking or interior water damage.
Resolving this requires adequate insulation and ventilation to keep roof surfaces uniformly cold. Following building codes like Calgary’s means roofs will be built to handle the normal amounts of snow, limiting danger. Proper compliance during construction or major renovation not only protects valuable property, but it protects people.
Recognizing Signs of Overloaded Roofs
Perhaps the most obvious indicator that a roof is overloaded is sagging. This could appear as a significant sag in the roofline or places where the ceiling looks lower than normal. Sagging is a sad but common indicator of a stressed structure, and it will continue to get worse if not repaired.
Creaking sounds are a second warning sign. These noises, especially when happening during or right after heavy snow, can indicate that a roof is overloaded and bending from the stress. Cracks in the ceiling or walls, even hairline ones, are signs of excess snow pushing down on your roof.
Heavy snow loading is a serious threat in Calgary, particularly in roof valleys or near chimneys, vents, and skylights. Snow has a tendency to accumulate in these areas causing an imbalance in weight distribution. Homeowners can look out for signs of new areas of snow that are deeper than 30-40 cm.
When removal is necessary, they should prioritize safe removal techniques. Water leaking or stains on ceilings are warning signs as well. You may see the signs in the form of dark patches or streaks on your roof. This is a sign that melting snow is finding its way through weak spots.
Routine inspections in winter months can be critical. Making a point to inspect your roof every few weeks or following a heavy snow can help identify these dangerous situations early on. Taking care of these minor problems early on will save you money in repairs and possible structural failure down the line.
How to Calculate Roof Snow Load
Knowing a few key variables and using a simple formula can help you calculate roof snow load. The basic formula is: Roof Snow Load (kPa) = Ground Snow Load (kPa) × Snow Density × Roof Slope Factor.
Ground snow load indicates how much snow is depositing on each square meter of ground. Snow density, on the other hand, is an indication of how compact or wet that snow might be. The roof slope factor allows you to make adjustments based on the pitch of your roof. Flatter roofs hold more snow load than steeper roofs.
It’s important to understand the different variables at play when calculating these figures. Ground snow load in Calgary can vary based on micro-climate snow fall.
Further, the wind exposure factor takes into account sections of the roof where wind can remove snow from the roof. Roof materials and insulation may play a larger role in preventing snow from accumulating and/or melting.
For example, a well insulated flat roof may hold more snow than a low slope metal roof. For accuracy, snow load calculator tools even take the hassle and guesswork out of considering these variables, automating the process for you.
For complicated roofs or special conditions, working with a roofing professional will guarantee the right answers. To address potential risks, their expertise can go a long way in determining if structural reinforcements are necessary or advisable.
Preventing Roof Collapse in Winter
Snow load on roofs can be a serious issue in Calgary’s bitter winters. Proactive snow removal techniques, such as the use of a roof rake, can allow you to manage the depth of the snow load without endangering roof structure. Roof rakes are very effective for one-storey homes and areas that are easy to access.
Here’s how homeowners can safely clear excessive snow after heavy winter storms to prevent roof collapse. Removing snow evenly as possible reduces the risk of creating imbalances that could stress the roof.
Installing snow guards is a practical step. These devices prevent snow, heavy accumulations, from crashing down off roofs in deadly avalanches, saving lives and property below. Snow guards are especially effective on metal roofs, as metal roofs are more prone to shedding snow.
With Calgary’s strong temperature swings, melting and refreezing snow is common. These tools add a measure of safety on days like that.
Clear gutters and downspouts are critical. When they’re free of debris, water from melting snow drains properly, which can help prevent ice damming and roof leaks. Heated gutter cables make great additions, too, by improving drainage and helping melt snow more quickly.
Regular winter inspections are just as important. These inspections prevent vulnerable areas, like weak seals or sagging sections, from going unnoticed and fix them before major problems arise. Keeping your attic insulated lets you maintain a stable temperature indoors, which helps prevent dangerous snow and ice from building up on your roof.
Tips for Winter Roof Maintenance
Winter in Calgary offers distinct challenges when it comes to maintaining your roof. Homeowners can save themselves the headache and expense of bigger problems by making the right choice. Other important winter maintenance tasks include clearing eavestroughs, making sure attic insulation is sufficient and trimming back any overhanging branches.
When their gutters are clean, water can flow freely, making ice buildup leaks a thing of the past. Good insulation keeps heat from escaping, which will help prevent snow from melting in some areas and refreezing in others. Ice dams are a typical worry throughout Calgary winters.
These occur when melted snow freezes at the edge of your roof, creating a dam that holds water behind it. Doing so will ensure that their roof is well ventilated, and homeowners can avoid this damage. Installing heating cables to prevent snow from freezing should be on their list. Routine inspections by trained roofing professionals are critical as well.
For example, a roof more than 20 years old might be beginning to crack or curl — signs that a trained eye can recognize before they become a serious issue. Another important step is to arrange for professional roof cleaning to get rid of debris that holds snow and moisture.
Clearing out heavy, wet snow with a roof rake can help avert serious structural stress. Last, but certainly not least, timely repairs are key. Taking care of any damage right away ensures the integrity of the roof, so you can rest easy all winter long.
Importance of Building Geometry and Wind Effects
Many factors influence the effects of wind on a building. The shape and slope of a roof are perhaps the most important when it comes to snow distribution. Increasing building geometry impacts, such as increasing pitch of roof, for example, causing more snow to slide off, leading to less accumulation overall.
Meanwhile, flatter roofs or those with complex designs, such as multiple peaks and valleys, often collect more snow in certain areas. This uneven distribution can lead to increased stress in specific locations. Things get especially dangerous when the snow load exceeds the building’s structural ability to support it.
In some Calgary residences, snow tends to become lodged between dormers and other roofline interjections. This produces greater localized loads that require additional scrutiny.
In addition to topography, wind exposure plays a huge role in determining where snow falls or stays on rooftops. Powerful winds frequently blast across Calgary’s vast prairies. They can effectively blow snow off parts of a roof while creating accumulations in other areas.
This can cause unbalanced loads, placing extra stress on one side of the structure. For example, slopes exposed to the prevailing winds will be mostly clear, whereas the side protected from the prevailing winds builds up deep drifts.
Coordination and skilled design during construction is critical to meeting these challenges. Building features such as reinforced, sloped framing or sloped, low-profile roofs make it possible to fight Calgary’s snow and wind situations.
Working with consulting structural engineers helps make sure these designs are structurally sound as well as cost-efficient.
