Calculating snow loads for roofs is a critical aspect of structural safety that often goes unnoticed until extreme weather conditions arrive. One of the primary reasons for calculating snow loads is to prevent roof collapse. Snow may appear light and fluffy, but it can put significant pressure on a structure as it accumulates. The weight of the snow can vary depending on factors such as moisture content, temperature, and type of snowfall. Engineers consider the ground snow load, which is the weight of the snow on the ground, and the roof snow load, which is the pressure on the roof. These calculations help design roofs that can support the maximum expected snow load, ensuring safety during winter storms.
Failure to properly calculate snow loads can lead to structural damage, property loss, and even pose a threat to human life. Roofs that are not designed to support the weight of accumulated snow can sag or, in extreme cases, collapse.
Calculating snow loads for roofs is not just a technical requirement. It is a fundamental step towards ensuring the safety and durability of a structure. In short, snow load is an important component in the strength design of a structure. Getting the loading right during the design phase ensures the safety of the structure.
Snow load is usually measured in kg/m². Snow depth can be obtained by multiplying the snow density by the snow depth. However, since it is difficult to know the exact density of each layer of precipitation on a snow-covered roof, here are some examples of snow loads depending on the quality of the snowpack:
In general, the weight of snow on a roof can be calculated using the formula: Snow weight = Roof length x Roof width / Slope degree x Snow load.
Unless the roof structure is weakened, most residential roofs should withstand a load of approximately 100 kg/m² before succumbing to structural stress.
Variables that affect the calculation of snow weight on a pitched roof include:
The European standard "EN 1991-1-3 Actions on structures - Part 1-3: General actions - Snow loads" provides guidance for determining the values of snow-induced loads used in the structural design of buildings and civil engineering works. This standard is not applicable to sites above 1500 m altitude unless otherwise stated. Recommendations for handling snow loads for altitudes above 1500 m are included in the annex of the standard. Annex A gives information on the design cases and load arrangements to be used for different locations. Annex B gives the shape factors to be used for handling exceptional snowpacks.
Annex C gives characteristic values of the snow load on the ground based on the results of studies carried out under a specific contract of the European Commission. The objectives of this annex are to:
Annex D provides guidance for adjusting ground snow loads based on the return period.
Appendix E provides information on the bulk weight density of snow.
The EN 1991-1-3 standard does not provide guidance on specialist aspects of snow load, such as:
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