The recent rash of tornado catastrophes across the country has left a path of obvious destruction. This is an example of the obvious damage:
What about structures that were not completely destroyed and those next to the most obvious destruction that remained standing? Did they escape the high winds and pressures without any damage?
A noted insurance company expert, Tim Marshall of HAAG Engineering, wrote a paper, Building Damage Issues in Tornadoes, which warns adjusters and policyholders to carefully inspect structures close to the tornado path for subtle but significant windstorm damages:
The assessment of property damage begins immediately after a tornado. Homeowners, insurance adjusters, contractors, engineers, and architects examine buildings and their surroundings to determine the extent of tornado damage. While catastrophic damage is easy to recognize, the more subtle signs of building distress are not.
The ever vigilant expert for insurers, Marshal notes that “inspectors often erroneously link these conditions to the storm.” My impression is that most inspectors fail to look for these subtle tornado damages which add up to sizable losses because they fail to do an adequate inspection, if any inspection at all.
Nevertheless, Marshall provides a good description of how high winds impact structures:
Tornadic winds encountering a building are deflected over and around it. Positive (inward) pressures are applied to the windward walls and try to push the building off its foundation. Therefore, it is important that the building be anchored properly to its foundation to resist these lateral forces. Negative (outward) pressures are applied to the side and leeward walls.
The resulting “suction” forces tend to peel away siding. Negative (uplift) pressures affect the roof especially along windward eaves, roof corners, and leeward ridges. These forces try to uplift and remove the roof covering.
The roof is particularly susceptible to wind damage since it is the highest building component above the ground. Wind pressures on a building are not uniform but increase with height above the ground.
I have found that the important aspect of damage caused by these winds is the fastening system of the structure. Nails, clips, joints, brick ties and other assorted connections tend to get pulled, bent, cracked or weakened by tornadic winds and pressure. These damages are often difficult to find and, once eventually discovered, can be expensive to repair. Buildings suffering these damages will age, deteriorate and increase maintenance costs at much faster rates than buildings not damaged by tornadoes.
Adjusters should retain honest and unbiased investigators to look for these subtle but significant damages. “Drive by” adjusting, without close inspection and possible testing, is improper for structures in the vicinity of a tornado’s destructive path. While the Marshall article tends to provide possible explanations why these damages may be related to perils other than windstorm, educated policyholders will ask their insurer to investigate for these serious damages.