Calculating Snow Load on Pitched Roofs: A Comprehensive Guide

Calculating snow load on pitched roofs can be a complex task, but it's essential to ensure the safety and integrity of your home. The load is determined by the roof's geometry, including the slope and orientation.

Snow load can vary significantly depending on the location, with areas near the equator receiving less snow than those closer to the poles. A roof with a steeper slope will have a lower snow load than one with a shallower slope.

In areas with heavy snowfall, the roof's design must be able to withstand the weight of the snow. A roof with a steeper slope will have a lower snow load, typically around 20-30 pounds per square foot.

The roof's geometry plays a crucial role in determining the snow load, and local building codes will often specify the minimum requirements for the roof's design.

Calculating snow load is crucial to determine if the structure can handle the snow's additional weight. You can calculate the snow load using the formula: Weight of snow = length of roof x width of roof / degree of slope x snow load.

The snow load is the additional weight on a roof structure added by snow and ice buildup on the roof. The ATC has a snow load hazard tool that can help you identify when a snow load presents a hazard to the structure.

To calculate snow load, start by measuring the roof's footprint to find the volume of snow on the roof. The volume of snow directly relates to how much it will weigh.

Most residential roofs should resist approximately 20 lb/ft² (100 kg/m²) before undergoing structural stress. If you get a result greater than 20 lb/ft² (100 kg/m²) with the calculator or formula, the snow has to be removed from your roof as soon as possible, because the structure of your roof is currently under great stress.

Here are the parameters you need to calculate the characteristic snow load:

Calculating snow load on a pitched roof involves several factors and coefficients that need to be considered. The snow load shape coefficient μi is one such factor that can significantly impact the calculation.

The value of μi can be decreased below 0.8 when the angle of the roof slope exceeds 30°, due to sliding of the snow off the roof. This is because the slope of the roof affects the amount of snow that stays on the roof.

For example, if the slope of the roof is 40°, the value of μi is reduced by 33.4% compared to a slope of 30°. This is calculated using the formula: μi = 0.8 × (60 – α) / 30, where α is the angle of the roof slope.

The following table summarizes the relationship between the roof slope angle and the snow load shape coefficient μi:

This table shows how the value of μi changes with the roof slope angle, and how it can be used to calculate the snow load on a pitched roof.

Coefficients play a crucial role in determining the weight of snow on a roof. The snow load shape coefficient μ1 is a key coefficient that affects the weight of snow on a roof.

For pitched roofs with an angle over 30°, μ1 can be decreased below 0.8 due to sliding of the snow off the roof. This is because the snow load shape coefficient μ1 is reduced by 33.4% when the slope of the roof is 40°.

The thermal coefficient Ct is another important coefficient that influences the weight of snow on a roof. However, Ct is defined as 1.0 in EN 1991-1-3 5.2 (8), and this value can be reduced if the roof is covered by glass, which would lead to melting of the snow.

Here are some coefficients and their corresponding values:

These coefficients are essential in calculating the weight of snow on a roof, and understanding their values and how they interact with each other is crucial for accurate calculations.

The characteristic value at ground level is a crucial factor in calculating the snow load on a roof.

The characteristic snow load on the ground can be found in the national annex of the country your roof is located in. However, there is a great online tool that calculates the snow load according to location and national annex.

For example, if we calculate the snow load for Copenhagen, Denmark, we get a value of 1.0 kN/m².

This value is then used to calculate the characteristic snow load of a pitched roof.

A pitched roof's slope is crucial in determining its snow load, with a steeper slope resulting in less snow accumulation. The steeper the slope, the less snow will sit on the roof.

A roof's pitch is often measured in terms of its rise over run, with a 4:12 pitch being a common example. This means for every 4 units of horizontal distance, the roof rises 12 units.

The type of roofing material used can also affect the snow load, with metal roofing being a good example of a material that can withstand heavy snow loads.

The length and width of a roof are crucial factors in determining its snow load. The larger the roof's dimensions, the greater the snow load will be.

The roof's surface area is calculated by multiplying its length and width together. This is expressed in feet or metres.

The dimensions of a roof are important for calculating its snow load. The formula used to determine the weight of snow on a roof relies on accurate measurements of length and width.

The surface area of the roof is directly related to its length and width. The larger the roof, the more snow it can hold.

The roof pitch plays a crucial role in calculating the weight of snow on a roof. The steeper the pitch, the lower the snow load will be.

If you've measured the roof's dimensions from the ground, you'll need to account for the roof pitch. This involves multiplying the area by the multiplier for the given roof pitch.

A list of multipliers can be found on a roofing calculator, which can also help you find your roof pitch if you don't know it. If the roof is a flat roof, then this step is not needed.

Before moving on, you'll need to multiply the area by the snow depth in feet to find the volume of snow on the roof.