Hail

Background

The majority of the structural damage caused in a severe thunderstorm occurs during a hailstorm. Hail damage to structures, foliage, vehicles, and agricultural crops is estimated to exceed $1-billion annually.

Hail that causes damage to structures is usually at least 1” in diameter. The larger the diameter of the hailstone, and the harder the stone, the more severe the impact on a building. The so-called baseball-sized hail causes more severe damage that the so-called golf-ball sized hail.

Vehicle damage can be caused by hail that is about .75” in diameter. Crop damage has been caused by hail as small as .25”.

Preventing Damage Roof damage is the most frequent structural loss caused by hail. Reducing roof damage that might result from a major hailstorm is possible. It depends on the type and quality, as well as the maintenance of the structure’s roofing system. It is a fact the cedar shake roofing is more likely to be damaged than 50-pound composite roofing material. The choice of roofing is a decision made by the building’s owner, although building code requirements sometimes restrict it.

Mitigating Damage after a Storm

Close any openings made in the structure by the hail. Broken windows are the most common problem. Keep a roll of plastic sheeting that can be quickly cut to size and nailed over the opening.

Openings in the roof and in siding from hail are rare. If they occur it is best to close them as soon as possible. Keep your personal safety in mind and attempt such a closure yourself only if it can be done with little or no risk. Your insurance policy will likely cover the cost of emergency close up. Contact your agent or claims center to report the damage and seek advice on how to proceed.

Wind

The number two cause of structural damage in a severe thunderstorm is from the so-called straight-line wind. This is wind moving in one direction and not rotating, such as a tornado.

Wind is considered severe when it reaches about 60 miles per hour. Some very severe windstorms can achieve a velocity of 100 miles per hour. Both are dangerous and will cause structural damage.

A form of wind that causes damage approaching that of a strong tornado is the downburst. This is usually in a very concentrated area. It is created by air blasting out of a thunderstorm to the ground beneath the storm cell.

Minimizing and preventing wind damage to a structure is possible. Roof and siding damage are the two leading types of loss following a windstorm.

Roof damage can be reduced during the construction phase when the roof deck and the shingles or membrane are applied over the decking. A well-designed roofing system will firmly anchor the trusses and decking to the walls and foundation to keep the entire roof from lifting off the building in a strong wind. Roofing material must be properly fastened to the deck. Weakly connected shingles will lift easily from the deck. Siding damage can be reduced at the construction phase as well. Properly fastened siding is less likely to lift off a structure in strong wind. Building codes will likely direct the minimum standards for connections. You, your architect, or your contractor may decide to exceed these minimums for a stronger and more storm resistant structure. Falling trees and tree limbs are another significant type of damage to structures in a windstorm. Tree maintenance to remove dead limbs or identify and remove weakened trees will reduce the likelihood of the structure being damaged.

Mitigating Damage after a Storm

Close any openings made in the structure by the wind. Roof openings and broken windows are the most common problem. Keep a roll of plastic sheeting that can be quickly cut to size and nailed over the opening.

Keep your personal safety in mind and attempt such a closure yourself only if it can be done with little or no risk. Your insurance policy will likely cover the cost of emergency close up. Contact your agent or claims center to report the damage and seek advice on how to proceed.

Falling trees and tree limbs can open a structure with sudden violence. A tree on a structure is a very serious personal and structural safety issue. A tree may look as if it will not shift position. But it can shift and cause serious injury to the unwary. A fallen tree may also mask other very serious safety issues, such as downed electrical wires. The wires may still be live and the tree itself energized. Contact your agent or claims center to report the damage and seek advice on how to proceed.

Tornadoes

A tornado is a violent rotating column of air. It originates in a severe thunderstorm as a funnel and dips to the ground. Once on the ground it is a tornado and a highly dangerous storm. About 1200 tornadoes occur annually, according to the National Weather Service. Fortunately most of them are the so-called weak tornado with winds of less than 110 miles per hour. While these will damage structures they cause few deaths. The most violent tornadoes, such as the storm that destroyed a swath of property in Oklahoma City and Moore, Oklahoma, during the 2003 season, are very rare. However they kill the most people and cause landscape clearing, catastrophic structural damage.

Please see the wind section for preventing and mitigating damage from a tornado.

Flooding

Flash flooding sometimes follows rain during a severe thunderstorm. This peril is the leading killer of people during the severe thunderstorms. The fatalities occur not in structures, but usually in vehicles and after dark. Drivers under estimate the depth of water, the energy of its velocity, and how easily a vehicle can begin floating in about 24” of water. Structural flooding typically occurs in areas that are known to be flood plains and have been mapped by the National Flood Insurance Program.