Snow, thaw and frost

Check exposed structures and get the meltwater away

Over the coming decades, we will gradually experience winters becoming warmer and wetter on average. In the milder climate, the increasing amounts of precipitation will more often appear as slush, which during a snowstorm can gather in heavy drifts and expose roofs and other structures to increased snow loads.

From experience, especially halls with large roof spans and wide roof surfaces, such as sports halls and warehouses for agriculture and industry, can be at particular risk of collapse. A collapse can happen if the structures’ dimensions are insufficient for the snow loads on them or if there is a weakening of the load-bearing capacity of the rafters or secondary structures, such as purlins or roof slabs.

An analysis made by The Danish Building Research Institute of 13 building collapses during the snowstorm in February 2007 highlights the type of buildings that are especially at risk. These were buildings sheltered by higher buildings, roof surfaces with large level jumps and local shelters, combined roof surfaces that can provide drift formations and roof surfaces with a risk of snow sliding down from higher roof surfaces. The snowstorm in February 2007 combined heavy snowfall, weak frost, and strong wind from the same direction for several days. This combination caused relatively heavy snow to drift in exposed places on the roof surfaces due to the weak frost and the strong and persistent wind from the east.

The snow-related collapses during the snowstorm in February 2007 resulted in tightening rules in the load standard. However, it only affects new buildings built after tightening the rules, and thus not existing buildings. Therefore, owners of buildings with exposed roof structures should check whether roofs and other exposed structures could support larger snow loads according to the new rules and ensure no weakening of the structures. An inspection can show whether there is a need for reinforcement of the constructions, local changes to the roof surface, or increased focus on snow removal or evacuation. Of course, collapsing roofs can have fatal consequences, but they can also cause costly water damage.

With the rising winter temperatures, fluctuations around the freezing point will become more frequent. Thus, the variability between periods of frost and thaw will be more significant. These temperature fluctuations increase the risk of meltwater entering basements, moistening structures, and frost damage when the water freezes again.

With more precipitation in winter, there is a need for more care to keep houses and buildings dry. Blowing snow can accumulate in attic rooms, where it can later thaw and lead to water damage. Quick and efficient drainage of rain and meltwater is necessary. Furthermore, removing snow from house walls, roofs, and attics is essential. Clean gutters and grates enable meltwater to run off. Likewise, ensure that the terrain regulation directs water away from the house.