Snow Load Calculator (Ontario)

Roof Length (m)

Roof Width (m)

Snow Load Factor (kPa)

In Ontario, roofs must be designed carefully. This is to make sure they can handle the weight of heavy snow. The National Building Code of Canada and the Ontario Building Code lay down the rules. They help architects and engineers calculate how much snow a roof can support.

Since 1941, the National Building Code has been updated regularly. A big update came in 1975, with the new Limit States Design (LSD) method. This approach puts a strong focus on safety for both Ultimate and Serviceability Limit States. It’s a change from the old style, the Allowable Stress Design method.

Figuring out how much snow a roof can hold is not easy. It depends on many things like snow depth, density, and the weather. Snow amount, wind, cold temperatures, cloud cover, and humidity all play a part. These make snow load calculations quite complex.

When planning a building’s structure, safety and cost are important. Safety factors help deal with different materials and loads. They adjust for unknowns and make the design less risky. Load factors also consider how often extreme events, like heavy snows, may happen.

Key Takeaways

The National Building Code of Canada and the Ontario Building Code provide the design requirements for roof structures under snow load.
The Limit States Design (LSD) approach, introduced in the 1975 edition of the NBC, emphasizes safety margins and replaces the previous Allowable Stress Design (ASD) method.
Accurately predicting snow loads is challenging due to the complex variables involved, such as snow accumulation, climatic conditions, and wind redistribution.
Structural design aims to balance safety and cost-effectiveness, with safety factors accounting for uncertainty and variability in materials and loads.
Load factors are increased to accommodate variability and the statistical return period of severe events, such as the 1-in-50-year snow load.

Introduction to Snow Load Design in Ontario

In Ontario, it’s vital to plan for snow loads when designing buildings. This ensures they stay safe under heavy snow and ice. The Ontario Building Code has specific rules for figuring out how much weight roofs can bear. It looks at things like the amount of snow on the ground, the direction of the wind, the roof’s shape, and its slope to set the right snow load. Following these rules carefully is key to making sure buildings are strong enough for Ontario’s cold winters.

Importance of Proper Snow Load Planning

Before 1965, people thought the snow on roofs was the same as on the ground. They didn’t consider how wind or the shape of the roof might change this. By the early 1960s, they started to realize that roofs could hold less snow than the ground. They changed the rules to consider these factors and reduce the snow load on roofs. With this change, the Ontario Building Code started to look at roofs more closely. They listed the weight of snow for roofs as 15 PSF in 1985 and then 18.75 PSF in 1990. Buildings that were built before this time need a special check by a Professional Structural Engineer to make sure they can handle the snow. Also, any place where people have fun, like ski slopes, must have their structures checked every 5 years by someone who knows a lot about building safety.

Overview of Building Code Requirements

The Ontario Building Code looks at many things when deciding how much snow a building should hold. It considers the snow’s importance level (\(I_s\)) and its ultimate limit state. Other key points are the ground snow load (\(S_s\)) and rain’s effect (\(S_r\)), the wind’s role (\(C_w\)), the roof’s basic snow load (\(C_b\)), and snow’s weight (\(γ\)). The code gives ways to find both the level snow should be on the roof and how much roofs can handle. It’s important to understand and use these rules to build safe structures in Ontario’s winters.

Parameter	Value
Importance factor (\(I_s\)) for snow load in the ULS at Low importance	0.80
Ground snow load (\(S_s\)) in Calgary, Alberta	1.10 kPa
Associated rain load (\(S_r\)) in Calgary, Alberta	0.1 kPa
Wind exposure factor (\(C_w\)) for the location not fully exposed to wind	1.0
Basic roof snow load factor (\(C_b\))	0.8
Specific weight of snow (\(γ\))	2.673 kN/\(m^3\)

Calculating Specified Snow Loads

Designing buildings in Ontario involves figuring out the right snow load. It’s crucial for the building’s safety. The formula to find the snow load, called “S,” looks like this: S = Is [Ss (CbCwCsCa) + Sr]. Each part of this formula helps keep the building strong.

Formula for Specified Snow Load

The snow load’s formula includes several important factors. They are:

Is – This factor changes with how important the building is (low, normal, high, or post-disaster).
Ss – The 1-in-50-year ground snow load for the area.
Cb – It’s about the roof size and its snow load.
Cw – This is the wind exposure factor, it changes with the building’s position.
Cs – The slope factor depends on the roof’s angle.
Ca – The shape factor considers uneven snow loads on some roofs.
Sr – It’s the rain load that comes with a 1-in-50-year frequency.

Factors Influencing Snow Load Calculations

Many things affect the snow load formula. This includes where the building is, the surroundings, and the roof’s shape. It’s key to check ASCE 7-10 for the right data.

Factor	Description	Example Values
Importance Factor (Is)	Varies based on the building’s importance category	Low: 0.8 (ULS), 0.9 (SLS) Normal: 1.0 (ULS), 0.9 (SLS) High: 1.15 (ULS), 0.9 (SLS) Post-disaster: 1.25 (ULS), 0.9 (SLS)
Ground Snow Load (Ss)	1-in-50-year ground snow load for the location	1.10 kPa in Calgary, Alberta
Basic Roof Snow Load Factor (Cb)	Accounts for the size of the roof	Default: 0.8 Adjusted for large roofs: 1.0 – (30/lc)² or 1.3 – (140/lc)²
Wind Exposure Factor (Cw)	Varies based on the building’s exposure to open terrain	Default: 1.0 Reduced to 0.75 or 0.5 in specific cases
Slope Factor (Cs)	Adjusts the load based on the roof’s slope angle	1.0 for α ≤ 30° (70° – α)/40° for 30° 0 for α > 70°
Shape Factor (Ca)	Accounts for non-uniform snow loads on certain roof shapes	Default: 1.0 Can be adjusted for specific roof shapes
Associated Rain Load (Sr)	1-in-50-year associated rain load	0.1 kPa in Calgary, Alberta

Engineers use these factors to find the right snow load for buildings. This ensures the building can handle the snow in Ontario.

Basic Roof Snow Load Factor

In Ontario, designing roofs involves a key factor – the basic roof snow load, Cb. For most roofs, this Cb is 0.8. Yet, for large roofs, it changes. This is to fit the roofs’ special needs.

When we talk about big roofs with lots of wind (Cw = 1.0) and a long length (lc), the Cb changes to 1.0 – (30/lc)^2. If the roofs are also very expansive, with Cw = 0.75 or 0.5, the Cb is 1.3 – (140/lc)^2. What’s lc? It’s a special length that measures 2w – w^2/l. Here, w stands for the shorter side, and l the longer side, of the roof’s measurement.

These special rules for the Cb factor make sure big roofs can handle heavy snow. This is crucial because big roofs face different snow risks than small ones. Factors like how much wind a roof gets and its size are key. These details help builders make sure their structures are strong in Ontario, no matter the weather.

Wind Exposure Factor and Its Impact

The wind exposure factor, known as Cw, is key in figuring out how much snow buildings in Ontario can bear. It really changes what rules the structure must follow and how strong it needs to be.

Open Terrain Considerations

For buildings not very important, the Cw can sometimes drop from 1.0 to 0.75 or 0.5 in windy, open spaces above the treeline. This shift happens when the building’s roof is hit by wind from all directions with no big blocks.

Exposure Levels and Adjustments

How much wind a building faces changes how snow piles up and drifts. This leads to tweaks in the snow load estimates. Where a building is located can up the snow’s weight it’s built to bear by up to 30%. Getting detailed weather facts is critical to nail the snow load needs.

Knowing how a structure can hold up against the wind is crucial for the snow load planning. Strong winds might actually mean less snow on the roof because it blows away. But where wind makes snow pile up, more support against that weight is necessary.

Figuring out the static wind and the winds on the outside of the building is a must. The size and shape of a structure can also lead to considering wind in unusual ways.

To wrap it up, the wind exposure factor, or Cw, is vital for setting the right snow load rules in Ontario. It’s all about adjusting for winds if the building isn’t very important but faces strong gusts in wide spaces.

“Accurate assessment of wind exposure and its impact on snow loads is crucial for the structural integrity and safety of buildings in Ontario.”

Accounting for Roof Slope

When we think about snow loads on roofs in Ontario, the roof’s slope matters a lot. This is because the slope of the roof changes how much snow it can hold. The slope factor, called Cs, helps us adjust the snow load. It considers how well the roof can let snow slide off.

Slope Factor for Different Roof Types

How steep a roof is, shown as α, helps us find Cs:

If α is 30° or less, then Cs is 1.0.
For roofs where 30°
Roofs steeper than 70° have a Cs of 0.

For roofs where snow and ice slide off easily, we calculate Cs this way:

If α is 15° or less, Cs becomes 1.0.
For roofs with a 15°
When α is 60° or more, Cs is 0.

The Cs factor helps roofs shed snow easier, affecting the snow load they must bear. The steeper the roof, the less snow it needs to support. This is why considering roof slope is very important for building stability.

“The reduction in design snow loads on steeper roofs in Canada can be traced back to the first National Building Code of Canada in 1941, with subsequent adjustments leading to the current NBC 1985.”

The NBC 1985 provides a way to lower the snow load based on roof slope, using a slope-reduction factor (Ce). It focuses especially on roofs that easily let snow slide down. This method ensures buildings in Ontario are safe and cost-efficient against snow load stresses.

Learning about how roof slope affects snow loads helps architects and engineers. It guides them in making smart choices for building designs in Ontario. This way, the structures will be ready for the challenge of the area’s weather.

snow load ontario

When we talk about snow loads in Ontario, the shape factor, Ca, is vital for safety. The default shape factor is usually 1.0. But, adjustments can be made to factor in non-uniform snow loads on specific roof shapes. These adjustments account for the unique aspects of the roof’s design. They make sure the snow load is accurate and prevents dangers.

Addressing Non-Uniform Snow Loads

Ca can be changed to deal with different snow load situations. Examples include:

More snow in valleys of gable, arched, or curved roofs
Increased loads from snow drifting onto lower roofs
More snow near projections like penthouses
Extra snow or ice from sliding or melting

Designers use these adjustments to accurately match snow load to roof conditions. This prevents structure damage and keeps people safe.

Adjusting Ca is essential because snow weight variances on a roof are significant. This is due to various factors like wind and melting patterns. Such changes make sure the building is ready for the snow’s weight. Therefore, it lowers the risk of a structure collapsing or any danger.

Knowing how important the shape factor is in Ontarian snow loads helps designers a lot. They can make buildings safer and more able to face winter’s challenges.

Large Roof Considerations

For big roof structures, we need to adjust the snow load factor, Cb. This is because snow can pile up and drift more. If a roof is long, Cb gets adjusted lower to deal with uneven snow loads better.

Snow Drifting and Accumulation Areas

The Ontario Building Code says that shorter roofs near taller ones must deal with 50% of the snow load from drifting. Getting this right is essential to prevent roof problems.

Big roof areas face a lot of snow dangers, especially in places like the Sierra Nevada Mountains. Snow loads there might hit 450 pounds-per-square foot. This can stress buildings a lot.

Roof pitch is vital for handling snowy areas. Metal buildings in snowy places should have pitches of 3:12 to 6:12. With the right pitch, snow can slide off better.

Metal roofs with a standing seam work well with a 2:12 or 3:12 pitch to help snow slide. Placing entrances under the gable, away from wind, cuts down snow drift impact.

Looking after gutters and downspouts in snowy areas is a must. Many RHINO customers choose to install them to avoid issues like ice dams.

Dealing with snow challenges is key for building safety in places like Ontario. Good construction and maintenance are vital to keep properties and lives safe.

City	Building Code (kPa)	Roof Snow Load (kPa)
Vancouver	4.3	1.7
Surrey	4.3	1.7
Richmond	3.1	1.7
Coquitlam	3.9	1.7
South Surrey	3.9	1.7
Langley	3.1	1.7

Different parts of Canada have unique snow load needs based on local climate and building details. Knowing these needs is key to avoid roof issues.

Figuring out the right snow load for your roof involves careful study. This ensures your building is safe during winter. Proper roof design, construction, and maintenance reduce the snow risk.

Conclusion

Calculating the right snow load for buildings in Ontario is vital during design. The Ontario Building Code helps figure out the needed snow load, S. It looks at ground snow load, wind exposure, roof slope, and roof shape. Meeting these rules helps ensure structures can take Ontario’s heavy snow and ice safely, keeping people and properties secure.

It’s key to know and use the snow load calculation rules well for building safety in Ontario. Snow can make roofs fail, as it’s a live load from snow’s weight. The snow’s weight changes a lot with moisture, from 3-33% for dry snow to 33-100% for wet snow or ice. Making sure buildings can handle the right snow load avoids big problems.

Ontario gets different snow because of its weather patterns. Rules for snow load change a lot across the province. By sticking to local laws, using the Ontario Snow Load Calculator, and getting expert advice, building planners can make sure their buildings are ready for the unique snow they might get.

FAQ

What is the formula used to calculate the specified snow load, S, for a roof or building surface in Ontario?

To find the snow load for a roof in Ontario, we use this formula: S = Is [Ss (CbCwCsCa) + Sr]. Is is the importance factor. Ss stands for 1-in-50-year ground snow load. Cb means the basic roof snow load factor. Cw is wind exposure. Cs is roof slope. Ca refers to roof shape. And Sr is the 1-in-50-year rain load.

What factors are considered in the snow load calculation for buildings in Ontario?

When figuring out snow load in Ontario, experts consider ground snow load. They also look at wind exposure, roof slope, and shape. These help decide the right snow load for each building.

How is the basic roof snow load factor, Cb, calculated for large roofs in Ontario?

The Cb factor for big roofs is figured out like this. Use 1.0 – (30/lc)^2 for Cw = 1.0 and lc ≥ 70 m. For Cw = 0.75 or 0.5 and lc ≥ 200 m, use 1.3 – (140/lc)^2. Here, lc is the roof’s characteristic length.

How does the wind exposure factor, Cw, impact the snow load calculation in Ontario?

Wind exposure with a factor Cw of 1.0 is common. It might drop to 0.75 or 0.5 for less important buildings. This is if strong winds without many obstacles hit the roof from all sides.

How is the slope factor, Cs, determined based on the roof’s slope angle in Ontario?

Roof slope angle, α, sets the Cs factor. When α is 30° or less, Cs is 1.0. From 30° to 70°, Cs becomes 0. For special roofs like unobstructed and slippery, there’s a different way to calculate Cs.

How are shape factors, Ca, used to account for non-uniform snow loads on certain roof shapes in Ontario?

In Ontario, shape factor Ca is often 1.0. But it may change for different roof types. For example, Ca might increase for valleys on specific roofs. It also changes for drifting snow and where snow slides.

How are large roofs in Ontario treated differently in the snow load calculation?

Big roofs in Ontario, over 70m with Cw = 1.0 or 200m with Cw = 0.75 or 0.5, have special rules. Their Cb factor decreases to adjust for uneven snow. Plus, lower roofs near these big ones must hold up against 50% of the snow load from drifts.

Snow Load Calculator (Ontario)