The aftermath of Irene is still uncertain in terms of total insured loses. In response to this certain uncertainty, Pie’s large-loss experts lend the following:
Based on Pie’s experience, damage to structures from hurricanes is generally a result of:
- storm surge
- coastal flooding
- or wind
Due to the fact that these types of damages are expected, building codes have included requirements for construction to provide life safety, an expected level of building performance, and damage control.
Storm surges typically result in damage to the lower levels of structures near the shoreline. Occasionally some structural components will remain, but are generally destroyed by secondary effects such as floating debris impacting other structures. Section C2.3.3 of the American Society of Civil Engineers (ASCE) Standard, Minimum Design Loads for Buildings and Other Structures addresses flood load criteria to be used in the design of structures near the coast. According to ASCE, “The flood load criteria were derived from an analysis of hurricane-generated storm tides produced along the U.S. East and Gulf coasts, where storm tide is defined as the water level above mean sea level resulting from wind-generated storm surge added to randomly phased astronomical tides.”
As we learned in our efforts with Katrina-related claims, it is difficult to find structures only damaged by wind and not water. In most instances, those roofs damaged by wind were typically due to the fact that current prescriptive code provisions requirements were not adhered to in the construction. Such violations of the minimum code requirements resulted in damage include; improper roof sheathing attachment to structural members, improper member connections to bearing walls, and improper use of insulation board sheathing in lieu of structural sheathing. In general, roof damage was due to improper uplift connections and attachments as required by the building codes. As well, damage that was latent such as deterioration of subbase material due to the improper installation of products became apparent, such as EIFS being stripped off of rotted underlayment and long-term corrosion of structural members.
According to the American Wood Council of the American Forest & Paper Association (AF&PA), the Wood Frame Construction Manual (WFCM) for One- and Two-Family Dwellings was introduced in response to Hurricane Andrew’s destruction in 1992. This manual provides building design for high wind areas, especially those structures near coastal areas. In general, the WFCM requires that a continuous load path be provided to transfer all wind and gravity loads from the roof, wall, and floor systems to the foundation. The WFCM also specified the use of raised wood floors to help prevent flood damage. Buildings can be built above ground level, such as on support piles, to allow for rising water levels without significant damage to the residence.
Coastal flooding and general flooding due to rain is another factor in assessing hurricane damages. Flood damage can translate into water damage to interior finish and contents. Unfortunately, many owners do not carry flood insurance. ASCE 7 provides the minimum requirements for determining flood loads and load combinations for buildings and structures located in flood hazard areas. ASCE 7 recognizes that the most important flood loads for structural design occur where the depth of flooding is greatest. The ASCE 7 load factor used in structural design (hydrostatic, stead flow, and wave forces) is based on calculations of still-water depths ranging from 4 feet to 9 feet and applies to a wide variety of flood conditions. In addition, ASCE 24 was developed to provide minimum requirements for flood resistant design and construction of buildings and structures located in flood hazard areas.
Hurricanes can also cause significant damage to structures due to wind. Based on our review of structure damage due to hurricanes, much of the damage could be prevented with proper design and construction that is in accordance with the adopted building codes and material guidelines and standards. Wind damage can cause uplift of structural components including roof system and front canopy system and also cause racking of light-framed structures. Lighter wind damage will typically consist of wall and roof covering damage in lieu of structural damages. Once the windows or door openings of buildings are broken or otherwise removed, the wind can pressurize buildings causing significant outward forces being exerted on the building, which was likely not designed for such outward forces.
We as forensic engineers, are typically asked to determine whether the observed structural damages were caused by wind or flood. Hurricane Irene will likely have similar claims as these damages will need to be attributed to the proper forces. In addition, there are commonly pre-existing conditions that exist within the structures that need to be identified and documented, which could be unrelated to the hurricane. A thorough structural analysis is needed to determine the contributory causes of the damage and to determine the extent of required repair.
According to an excerpt from this week’s Insurance Journal: https://www.insurancejournal.com/news/national/2011/08/29/212709.htm
“Hurricane Irene is expected to have caused substantial property losses, though figures are still hard to come by because of uncertainty about wind damage, catastrophe modeling company Eqecat said Monday.
The storm may have been something of a worst-case scenario for large U.S. property insurers like Allstate Corp. and Travelers Companies Inc., some analysts said, enough to wipe out some or all of their third-quarter earnings, but not enough to cause an industry-wide increase in prices after years of weakness.
Yet shares in Allstate rose 7 percent and Travelers rose 5 percent in morning trading, in line with European insurers which rose on relief that the damage from Irene was not as bad as feared. Other insurers were also higher, ahead of gains in the broader market.
Millions of people throughout the northeastern United States were still flooded and without electricity Monday morning, particularly in rural Vermont and suburban New Jersey. Totaling those losses is expected to take time, as is the process of figuring out how many of the affected had government-backed flood insurance.”
- Sandy likely to be a multi-billion dollar disaster for the U.S. (wunderground.com)
- Conn. Homeowners Find Destruction In Sandy’s Wake (connecticut.cbslocal.com)
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