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Snow Load Calculator

Estimate the weight of snow on your roof based on your location's ground snow load, roof pitch, and building importance.

Find this value from your local building department or snow load maps.

Understanding Roof Snow Loads

Knowing the potential snow load on your roof is crucial for structural safety, especially in regions with heavy winter snowfall. Accumulated snow can exert significant weight, potentially leading to structural damage or even collapse if the roof isn't designed to handle it.

Key Factors Affecting Snow Load

  • Ground Snow Load (Pg): This is the baseline weight of snow on the ground for a specific geographical location, measured in pounds per square foot (psf). It is determined by historical weather data and is specified in local building codes.
  • Roof Pitch: The steepness of your roof affects how much snow accumulates. Steeper roofs tend to shed snow more easily than flatter roofs. This calculator applies a slope adjustment factor:
    • Pitch ≤ 4/12: Factor of 1.0 (little to no shedding)
    • Pitch > 4/12 and ≤ 8/12: Factor of 0.9
    • Pitch > 8/12 and ≤ 12/12: Factor of 0.8
    • Pitch > 12/12: Factor of 0.6 (significant shedding)
  • Importance Factor: This factor accounts for the risk to human life and the importance of the structure to the community. Essential facilities like hospitals have a higher factor (e.g., 1.2) to ensure greater safety margins compared to standard residential buildings (1.0) or low-hazard structures like barns (0.8).

Example Calculation

Let's say you live in an area with a ground snow load of 40 psf. You have a standard residential home (Importance Factor = 1.0) with a roof pitch of 6/12.

The calculator would first determine the slope adjustment factor for a 6/12 pitch, which is 0.9.

The estimated roof snow load would be: 40 psf (Ground Load) × 0.9 (Slope Factor) × 1.0 (Importance Factor) = 36 psf.

Disclaimer: This calculator provides a simplified estimation for educational purposes only. It does not account for factors like wind exposure, thermal conditions, or snow drifting, which can significantly increase loads. Always consult a qualified structural engineer for accurate snow load determination and structural assessments.

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