Snow load - How much snow can a roof withstand

Snow load – How much snow can a roof withstand

Winter can bring sparkling white snow and realize a winter fairy tale. But winter can also cause a roof collapse due to too much snow. In this case, the snow load was too high for the roof. Find out exactly what a snow load is, why it’s so dangerous, and how you can winterize your roof!

Snow load – What is it?

An area load consisting of snow perpendicular to the base of a structure, which can vary by climate and region, is called a snow load. The snow load indicates the maximum weight of the snow layer on a square meter of roof surface in order not to be a danger to the load-bearing capacity of the roof structure. Otherwise, the formation of snow bags due to improper design of the roof structure can cause the roof to collapse.


Have a roofing expert check if the structural integrity of your roof can withstand the snow load in your area. Both after a winter with high snow loads and before the onset of winter, a professional should be hired to inspect the roof structure so that any damage to the roof tiles, roof insulation, as well as the snow guards for shingle roof can be repaired.

What factors are important for snow load?

Roof pitch, roof shape and special roof structures such as dormers are important in calculating the snow load that is allowed on a home. When it snows long and hard, snow “piles up” in layers on the roof. This accumulation of snow can turn into ice on the roof at sub-zero temperatures, respectively, the snow does not melt. The danger of snow load depends on the type and density of snow. New snow has a density of 100 kilograms per cubic meter, while old snow has a density of 300 kilograms per cubic meter.


If you are going to build a house, garden shed or carport yourself, you need to calculate in advance what the snow load is in your area and take it into account when building your roof. To increase the snow load of a purchased garden shed or carport, in many cases you can be supplied with thicker posts for an additional cost in the market.

Don’t forget about keeping your roof clean, either. Use a pressure washer for car. It is suitable for washing your car, house, roof, walls and yard.

How is a snow load calculation done?

Snow load zones – also referred to as local snow load – are included in the snow load calculation and take into account the climate zone and topographic elevation in which the area is located. In addition to the local snow load, a so-called shape coefficient also plays a role, which results from the roof shape and pitch. The flatter a roof is built, the greater the snow load will be. The permissible snow load can be calculated by multiplying the two values mentioned above (local snow load and shape coefficient).

What danger does the snow load pose to the roof?

The following can be stated as a basic assumption for snow loads: The higher the building is geographically, the higher the snow load should be assumed to be. The steeper the roof, the less snow can accumulate on the roof as it slides off due to gravity.


Regardless of how strong your roof’s load-bearing capacity is, professional roof clearing should be done for safety reasons.

Accordingly, houses with a flat roof, such as the carports, the terrace roofing, the porch roof and the roof of the garden house are particularly affected by the problem of snow load. Because here it is more likely that a roof collapse will occur due to the snow.

What can be done if the snow load is too high?

If the permissible snow load is reached or even exceeded, the roof must be cleared as quickly as possible. If you are not able to do this yourself, it is advisable to call a company that specializes in roof clearing. If possible, the snow should be removed from the individual roof surfaces in sections and evenly, in order to counteract any stability problems that may arise.

The owner can often remove the snow accumulation from the porch roof and the flat roof of the garden house himself, because these low roofs are more accessible and their roof clearing is less risky than roofs of carports or patio covers. With steep roofs, on the other hand, the snow load is usually less of a problem. Here, the problem lies more in the fact that roof avalanches can occur. However, these can be counteracted with the help of a snow guards for standing seam roof.

Snow can have a strong impact on roofs, so roof clearing should be carried out. For low houses, such as garden houses, the owner can do roof clearing himself. For higher roofs, the help of a roofer should be commissioned, because the risk of injury is too high due to your lack of experience and expertise.

How to winterize a roof?

Roof clearing can be done professionally in winter, but roof clearing alone is not enough. A roof inspection should also be performed regularly in the spring, or especially after a harsh winter, to detect early if the roof has any damage. A roof inspection tends to be inconvenient in the winter due to temperatures and precipitation, so it should be done after the winter.


The allowable snow load provides information on how much snow a roof can support without compromising structural integrity. This value can be calculated on the basis of a local snow load and a so-called shape coefficient. Particularly in the event of heavy snowfall, it is important to have the current snow load checked and to initiate roof clearance if the permissible snow load is exceeded.

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Christophe Rude

Christophe Rude

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