Hurricane Charley Validates New Building Code

Charley was now bearing down on the Fort Meyers area much further south than expected as a Category 4 hurricane, making Charley the most severe hurricane to make landfall in the United States since Hurricane Andrew in 1992.

While the storm was extremely powerful, it was also quite small. As hurricanes become more "tightly wound," they typically intensify, particularly near the center of the storm. Charleys radius of maximum winds dropped from roughly 12 miles as it approached the coast to about six miles as the eye crossed the barrier islands, increasing again to 20 miles by the time it reached Orlando. The resulting swath of the most severe damage was a mere 15-to-20 miles wide. Moderate-to-light damage extended only about 25 miles from the center of the storm.

Hurricane Charley was an unusually fast-moving storm for this region, with an average forward speed exceeding 25 mph. While this actually kept the level of damage at any given location lower than it might otherwise have been, it also resulted in the penetration of high winds well inland. In fact, Charley maintained hurricane force winds throughout its path across Florida, exiting near Daytona Beach, more than 200 miles from its initial landfall location, as a Category 1 hurricane.

The AIR post-disaster survey team traveled Charleys path from Sanibel Island and Charlotte Harbor on the west coast of Florida through Orlando. The coastal counties of Charlotte, Lee and De Soto were the hardest hit and therefore the focus of this report.

The Impact of Floridas New Building Codes

AIR estimates that approximately 60 percent of Charley's insured loss will come from residential properties. A majority of these losses occurred in the three coastal counties that took the brunt of the storm's most intense winds. There is little doubt, however, that losses would have been even higher were it not for actions taken by the state of Florida in the aftermath of Hurricane Andrew.

Florida's newest building code, officially enacted in 2002, requires builders to construct residential properties to a much higher standard than in pre-Andrew days. The new code toughened the requirements both for overall building design and "prescriptive" design which governs, for example, the detailing of joints and connections. Roofs must be held in place by hurricane straps. Roof tiles and sheathing should be nailed down using proper nail size and spacing.

Another important measure was the designation in coastal areas of "windborne debris zones." Properties built in such zones are required to protect windows using shutters or impact-resistant glass.

Hurricane Charley provided the first real test of the new code, and it is AIR's assessment that structures built to the code held up quite well overall.

Accompanying this article are photos of two houses located within a few blocks of each other in Punta Gorda. The house on the left was built to the new, stringent Florida building code. It is of masonry construction and its roof tiles are well fastened. The house on the right, which suffered severe damage, is of wood frame and unreinforced masonry construction, and built before the new building code was implemented. As expected, masonry houses fared much better than wood frame, with very few suffering wall failure.

As in the case of residential structures, commercial properties built within the years since Andrew fared much better than older structures. In particular, newer framed roof structures though not entirely unscathed held up much better than those built under the older building codes.

AIR estimates that roughly 30 percent of property losses from Hurricane Charley are to commercial buildings, which are, in general, less vulnerable than residential buildings because of the engineering attention they receive.

Taller Buildings Fared Better

The AIR team also found significant differences between the performance of taller commercial buildings and low-rise commercial buildings. Because taller buildings can be expected to face greater wind loads, such buildings are better "engineered." That is, building codes and construction practices are more stringent.

On the other hand, taller buildings tend to have more glazing (glass windows and cladding) which is particularly susceptible to damage from windborne debris. Building height, then, is an important parameter in hurricane vulnerability modeling.

Roof type played a big role in the amount of damage suffered by commercial structures. Flat concrete slab roofs, commonly used on taller buildings, held up much better than did the lighter roofing materials characteristic of low-rise structures, such as older strip malls and warehouses.

Andrews Legacy: An Industry Better Prepared

Hurricane Charley left thousands of people temporarily homeless and made life extremely uncomfortable for tens of thousands more. It will be months before a sense of normalcy is restored.

Still, it is clear that both property owners and insurers are better prepared today than they were when Hurricane Andrew devastated parts of south Florida in 1992. One reason is the now almost universal use by the reinsurance industry of computer modeling to assess and manage potential losses from natural catastrophes.

By combining mathematical representations of the natural occurrence patterns and characteristics of hurricanes, tornadoes, severe winter storms, earthquakes, and other catastrophes, with information on property values, construction types, and occupancy classes, these simulation models provide information concerning the potential for large losses before they occur. By anticipating the likelihood and severity of potential future catastrophe events, companies can appropriately prepare for their financial impact.

Models have evolved to a high level of resolution, able to account for the detailed risk characteristics of individual properties, such as storm shutters, enhanced roof strength and impact resistant glazing. This makes models even more important today, as building codes and construction practices also evolve, giving insurance companies the ability to rationally price credits for policyholders who take action to mitigate their potential property damage.

Atul Khanduri is manager of wind risk modeling at AIR in Boston.

Mobile Homes Pose Unique Storm Challenges

Hurricane Charley provided further confirmation that mobile homes are highly vulnerable to Category 3 or 4 hurricane winds. Mobile home losses in many of the most heavily impacted areas were close to 100 percent.

On the other hand, it is worth noting that the most severe damage occurred in communities built before the new building code took effect. While the wreckage, at times, was so complete that it was difficult to sift through, AIR's survey team noted the absence, in many cases, of anchored tie-downs. While such mitigation devices would have only a marginal impact on mobile home losses in the face of a Category 4 hurricane, they can be critical in lesser storms.

While the loss to mobile homes was not surprising given the severity of this storm, lessons can still be drawn. AIR's investigation suggests that the primary reasons for such catastrophic failure can be attributed to two building attributes that performed miserably:

The building frame was typically light wood, which does not hold up well to winds in excess of 120 mph.

Even in the few instances where the frame survived, vulnerable building materials like thin metal cladding and roofing were peeled away, exposing the contents to the elements.

Reproduced from National Underwriter Edition, September 9, 2004. Copyright 2004 by The National Underwriter Company in the serial publication. All rights reserved.Copyright in this article as an independent work may be held by the author.