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How to Calculate Snow Load in Ontario

Reviewed by Calculator Editorial Team

Calculating snow load in Ontario is essential for structural engineering and building design. This guide explains the Ontario Building Code (OBC) requirements, key factors, and provides a calculator to determine snow load based on location and building characteristics.

Introduction

Snow load is the weight of snow that a structure must support during a snowfall event. In Ontario, building codes require engineers to calculate snow load to ensure structures can withstand the weight without collapsing. The Ontario Building Code (OBC) and Canadian Standards Association (CSA) standards provide guidelines for determining snow load.

The snow load calculation considers factors such as geographic location, roof slope, exposure, and thermal properties of the building. Engineers use this information to design roofs, walls, and foundations that can safely support the expected snow load.

Snow Load Formula

The snow load (S) in Ontario is typically calculated using the following formula:

S = Ce × Ct × Cs × G

Where:

  • Ce = Exposure factor (accounts for wind and terrain)
  • Ct = Thermal factor (accounts for building insulation)
  • Cs = Slope factor (accounts for roof slope)
  • G = Ground snow load (varies by location)

The ground snow load (G) is determined based on the geographic location in Ontario. The Ontario Building Code provides specific values for different regions.

Key Factors Affecting Snow Load

Several factors influence the snow load calculation in Ontario:

  1. Geographic Location: Different regions in Ontario experience varying amounts of snowfall. The ground snow load (G) is higher in areas with more snowfall.
  2. Roof Slope: Steeper roofs shed snow more easily, reducing the snow load. The slope factor (Cs) accounts for this.
  3. Exposure: Buildings in open areas experience higher wind exposure, which can increase the snow load. The exposure factor (Ce) accounts for this.
  4. Thermal Properties: Well-insulated buildings retain less snow, reducing the snow load. The thermal factor (Ct) accounts for this.

Step-by-Step Calculation

To calculate the snow load, follow these steps:

  1. Determine the Ground Snow Load (G): Look up the ground snow load for your location in Ontario. The Ontario Building Code provides specific values for different regions.
  2. Apply the Exposure Factor (Ce): Choose the appropriate exposure factor based on the building's location and wind exposure.
  3. Apply the Thermal Factor (Ct): Determine the thermal factor based on the building's insulation and thermal properties.
  4. Apply the Slope Factor (Cs): Choose the slope factor based on the roof's slope.
  5. Calculate the Snow Load (S): Multiply the factors together to get the snow load.

Use the calculator in the sidebar to perform these calculations quickly and accurately.

Worked Examples

Here are two examples of snow load calculations for different scenarios in Ontario:

Example 1: Residential Building in Toronto

Given:

  • Location: Toronto (Ground Snow Load, G = 3.0 kPa)
  • Exposure: Partially Exposed (Ce = 1.1)
  • Thermal: Moderate Insulation (Ct = 1.0)
  • Slope: 30° (Cs = 1.1)

Calculation:

S = Ce × Ct × Cs × G

S = 1.1 × 1.0 × 1.1 × 3.0

S = 3.63 kPa

Result: The snow load for this residential building in Toronto is 3.63 kPa.

Example 2: Commercial Building in Sudbury

Given:

  • Location: Sudbury (Ground Snow Load, G = 3.5 kPa)
  • Exposure: Fully Exposed (Ce = 1.2)
  • Thermal: Poor Insulation (Ct = 0.9)
  • Slope: 15° (Cs = 1.0)

Calculation:

S = Ce × Ct × Cs × G

S = 1.2 × 0.9 × 1.0 × 3.5

S = 3.78 kPa

Result: The snow load for this commercial building in Sudbury is 3.78 kPa.

Frequently Asked Questions

What is the minimum snow load requirement in Ontario?
The minimum snow load requirement in Ontario is typically 2.0 kPa, but this can vary based on location and building type. Engineers should refer to the Ontario Building Code for specific requirements.
How does roof slope affect snow load?
Steeper roofs have a lower slope factor (Cs), meaning they experience less snow load because snow slides off more easily. Flatter roofs have a higher slope factor.
What is the difference between ground snow load and roof snow load?
The ground snow load (G) is the amount of snow that would accumulate on the ground. The roof snow load (S) is the actual load on the roof, which is calculated by applying exposure, thermal, and slope factors to the ground snow load.
How do I determine the ground snow load for my location?
You can find the ground snow load for your location in Ontario by consulting the Ontario Building Code or using the calculator provided on this page. The values are typically provided for different regions.
What happens if the calculated snow load exceeds the building's capacity?
If the calculated snow load exceeds the building's capacity, engineers must design the structure to support the additional load. This may involve reinforcing the roof, walls, or foundations.