Snow Load Calculation Ontario

Introduction

The Ontario Building Code (OBC) provides guidelines for calculating snow loads on buildings. Snow load is a critical factor in structural design, especially for roofs and walls. Understanding how to calculate snow load ensures compliance with safety regulations and prevents structural failures.

Key factors in snow load calculation include the building's location, exposure, height, and type. This guide explains the Ontario Building Code's approach to snow load calculation and provides a practical calculator for accurate results.

Snow Load Formula

The Ontario Building Code uses the following formula to calculate snow load:

Each factor in the formula accounts for different aspects of snow accumulation:

• Ground Snow Load: The average snow load for the region (kPa)
• Exposure Factor: Adjusts for building exposure (1.0 for sheltered, 1.2 for partially exposed, 1.5 for fully exposed)
• Thermal Factor: Adjusts for building thermal properties (1.0 for heated buildings, 0.8 for unheated buildings)
• Importance Factor: Adjusts for building importance (1.0 for standard buildings, 1.25 for essential facilities)
• Roof Shape Factor: Adjusts for roof shape (1.0 for flat roofs, 1.2 for sloped roofs)

How to Calculate Snow Load

Step 1: Determine Ground Snow Load

Ground snow load values vary by region in Ontario. Refer to the Ontario Building Code tables for specific values based on your location.

Step 2: Apply Exposure Factor

Consider the building's exposure to wind and snow:

• Sheltered (e.g., behind large buildings or hills): 1.0
• Partially exposed (e.g., near open areas): 1.2
• Fully exposed (e.g., open fields): 1.5

Step 3: Apply Thermal Factor

Heated buildings retain more snow than unheated ones:

• Heated buildings: 1.0
• Unheated buildings: 0.8

Step 4: Apply Importance Factor

Essential facilities require higher snow loads:

• Standard buildings: 1.0
• Essential facilities (e.g., hospitals, schools): 1.25

Step 5: Apply Roof Shape Factor

Sloped roofs accumulate more snow than flat roofs:

• Flat roofs: 1.0
• Sloped roofs: 1.2

Step 6: Calculate Final Snow Load

Multiply all factors together to get the final snow load in kilopascals (kPa).

Worked Examples

Example 1: Standard Sheltered Building

Ground Snow Load: 0.7 kPa
Exposure Factor: 1.0 (sheltered)
Thermal Factor: 1.0 (heated)
Importance Factor: 1.0 (standard)
Roof Shape Factor: 1.2 (sloped)

Example 2: Essential Exposed Building

Ground Snow Load: 1.0 kPa
Exposure Factor: 1.5 (fully exposed)
Thermal Factor: 1.0 (heated)
Importance Factor: 1.25 (essential)
Roof Shape Factor: 1.0 (flat)