The calm before the storm. Now is the time to take precautions!

The best way to reduce windstorm damage in the medium to long term or even to prevent it altogether is to improve the resilience of buildings and their components to wind. It also requires making appropriate changes to infrastructure installations like bridges and means of transport (e.g. vehicle aerodynamics).

For the purposes of loss minimisation, all structural components must be built to withstand the additional loads generated during a storm blowing at design wind speed. Both static and dynamic forces must be considered, because during a windstorm buildings are exposed to extremely volatile streams of air that are constantly changing in strength and direction.

Bad weather calls for good architecture

The influence of the wind on buildings is not onesided: wind flow is also influenced by the buildings themselves. The vortices coming off the edges and corners of a building intensify the load on it.

The resonance behaviour of the building also plays a role. If it is an elastic structure with little damping, strong vibrations can develop even when wind speeds are relatively low. The constant trend towards making buildings bigger and lighter has led to them being increasingly susceptible to vibrations.

What can be done to slow down or even halt this loss-producing development? Here are some typical causes of damage and the corresponding loss prevention measures:

Roofs

The roof is the part of the building that is most frequently affected by windstorm damage. The reasons for this are:

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  Wind speed increases with height. Sharp or protruding roof edges generate wind vortices.
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  Roofs, chimney stacks, roof superstructures, and aerials, etc. are often not integrated securely into the loadbearing structure of the building and/or do not receive proper maintenance.

In order to avoid windstorm damage to roofs in the long term, the following measures are recommended:

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  When there is extensive roof cladding (e.g. corrugated sheet metal), screw it to the load-bearing construction. Otherwise, fasten the individual roof elements or roofi ng tiles flexibly.
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  Anchor the roof construction in the masonry using wall anchors, screws, and metal straps. Simple nails are not suitable.
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  Building aerodynamics: Roofs that are too fl at or too steep or protrude too far should be avoided. This will also reduce the pressure and suction forces of the wind.
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  Prudent gardening: Sufficient distance will protect the building from windstorm damage caused by falling trees.
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  Supplies of materials: Replacement roof panels or membranes make it possible to carry out fast repairs and provide (at least temporary) protection against the elements.

Exterior walls, façades

Damage to the exterior walls of buildings usually occurs only in particularly intense windstorms. However, losses are accumulating due to the increasing use of expensive and at the same time sensitive wall-facing materials. Unlike conventional façades with masonry or plaster, these are easy prey for the wind – a really alarming development. It makes no difference whether they involve insulation against heat loss and moisture penetration (in the form of glued or screwed materials, metal plates, or pressed plates) or whole façades made of light metal or plastics.

Precautions that can be taken to prevent damage to exterior walls and façades:

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  Anchor insulation and façade elements in the loadbearing structure of the building.
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  Avoid soft façade materials in areas exposed to hail.
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  Mount large-scale glass elements flexibly.
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  Ensure that the building is securely anchored in the foundations.

Protecting mobile facilities against bad weather

Scaffolding, cranes

Scaffolding and cranes are typical storm-prone temporary structures, as are air domes (covers without any supporting structure, which are kept stable by internal pressure) and tents. Strangely enough, inadequate attention is often paid to anchoring these structures in the ground, with the result that scaffolding or cranes not only suffer severe damage themselves during a storm but also cause damage to parked cars or other buildings in the immediate vicinity if they fall down. People are frequently injured, too.

The following loss prevention measures are available:

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  Secure the scaffolding to the buildings both during construction and in the course of repair work.
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  Replace worn, corroded, or other unsafe components and make regular controls.
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  In the case of cranes that run on rails, anchor the chassis to the rail foundation with bolts and latches.
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  Unlock the jib on a tower crane to permit flexible alignment to the wind.
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  A general rule regarding cranes is always to check the bearing capacity of the ground, particularly in view of the severe one-sided load during windstorms. If necessary, they should be secured with a cable-tensioning system.

Motor vehicles, caravans

The insurance industry is always hit by extensive losses in the motor own damage sector when there is a major windstorm event. In regions with a high property insurance density, the sum total of motor own damage losses frequently amounts to 5–10% of the total insured loss. This rate may also be considerably higher in emerging markets. Losses are primarily the result of falling trees or branches, roof panels, or façade components.

Possible prevention measures:

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  Put vehicles in the garage when there are storms or severe weather warnings.
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  When there is a danger of heavy storm gusts, close particularly exposed road sections and bridges to large lorries and caravans.
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  At camp sites, secure caravans with cables.
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  In hail-prone areas, protect car depots with hail nets.
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  A general rule is to repair damage quickly in order to avoid corrosion and other consequential damage.

Windstorm losses can be reduced considerably or even prevented by precautionary measures. The most effective way to prevent losses, however, is to incorporate the factor of wind resistance in the planning of infrastructure installations and all buildings and their individual components. Landuse restrictions in heavily exposed areas like those on the coast are also of special significance.