Damage to buildings during a storm obviously varies according to the construction and location of the building, but damage generally occurs above Force 9 or 10. Chimney pots, roofing tiles and slates are the parts of buildings most at risk from storm damage.
As wind passes over and around a building, two things happen. First, positive wind pressure applies to building components on the side(s) of the building that face the incoming wind (the “windward” direction). The windward wind load is essentially the force of the blowing wind pressing on the building. Second, negative wind pressure applies to building components on the side(s) of the building that face away from the incoming wind (the “leeward” direction). The negative wind pressure is also known as “suction.” The suction force will be applied to vertical surfaces such as walls, and also horizontal or sloped surfaces such as roofs. The suction force can be thought of as acting like a vacuum that pulls on a building and its components.
During an event with moderately strong winds, building materials such as asphalt shingles or vinyl siding may displace away from the building. Sometimes, windows break and the broken shards end up outside of the building. In such cases, a common misconception held by many people in the construction industry is that wind must have gotten under or behind the surface of the material to “blow” it out. However, acknowledging and understanding the concept of wind suction can explain how those materials were damaged. Wind does not only apply a direct blowing force on buildings, but it also induces a suction force. Depending on various factors, the suction force can be significant enough to cause damage to individual building components or the structure of the building itself.
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