Hurricanes Harvey and Irma IBHS Preliminary Findings Report

Transcription

1 IBHS Members Only Hurricanes Harvey and Irma IBHS Preliminary Findings Report Tanya M. Brown-Giammanco, Ph.D.

2 Introduction Following Hurricane Harvey, the Insurance Institute for Business & Home Safety (IBHS) deployed a team to the first landfall location northeast of Corpus Christi, Texas, to survey and assess wind damage to residential and commercial properties across multiple, wind-speed zones. Investigations were not conducted in the flooded areas of Houston. Access to wind-speed data obtained through Risk Management Solutions RMS HWind and the measurement and radar teams from University of Florida and Texas Tech University was invaluable to planning the exact deployment locations. The considered wind-speed data and the damage survey locations are provided in Figure 1. Figure 1. The RMS HWind Peak 3-second Gust wind-speed analysis, University of Florida and Texas Tech University wind-speed measurement locations, and IBHS damage survey areas from Hurricane Harvey. Wind-speed data were provided courtesy of each organization. 2

3 An IBHS damage survey team was not deployed for Hurricane Irma in Florida. However, the IBHS lead research meteorologist, Ian Giammanco, was part of the Texas Tech University Hurricane Research Team, which deployed meteorological instruments into the path of Irma, and he provided insights into the damage observed on the mainland of Florida during instrument pickups after the event. Collaborators from other universities and organizations have also provided damage insights from Irma, including some specific to the performance of FORTIFIED residential structures from the west coast of Florida. The wind-speed data and locations of the FORTIFIED properties are included in Figure 2. Figure 2. The RMS HWind Peak 3-second Gust wind-speed analysis, University of Florida and Texas Tech University wind-speed measurement locations, and IBHS FORTIFIED property locations from Hurricane Irma. 3

4 Key Observations 1. Wind damage from Hurricane Harvey in the surveyed areas ranged from the total destruction of buildings to façade damage (roof covering, fascia, soffits, siding) to no visible damage. Surge heights in the areas surveyed by the IBHS team were generally limited to less than 2 ft, other than in Holiday Beach. a. Total destruction from wind occurred to mobile homes, as well as older site-built conventional homes and light commercial structures including all-metal commercial buildings typically with large, unprotected commercial doors. 2. Wind damage from Hurricane Irma also ranged from total destruction of buildings to no visible damage, and the most substantial damage occurred in the Florida Keys. Flooding was more problematic than in areas surveyed by IBHS after Hurricane Harvey, excluding Houston. a. Total destruction from wind was generally limited to mobile homes. b. The most severe damage to site-built conventional homes was roof structural damage and some wall structural damage, but total destruction was uncommon. c. Damage to commercial structures was generally limited to roof covering loss. 3. Exposure affected wind performance. a. Buildings subjected to winds directly off the water were more severely damaged and more likely to have structural damage than those located inland. For the areas surveyed in Texas, this was generally winds off the bays as opposed to off the oceanside. b. Thick tree coverage in Texas likely helped to moderate and lessen the wind speeds experienced at inland areas; this would be considered beneficial, except in the instances where trees fell directly onto buildings or power lines. 4. Mobile home damage was substantial in both storms. The field damage assessment team did not investigate the factors that contributed to specific failures from high-wind conditions, the foundation design or anchorage of these structures, or whether they were constructed to high-wind zone requirements and sited accordingly as established under the U.S. HUD Part 3280, Manufactured Home Construction and Safety Standards. 5. Newer buildings generally performed better than older buildings as illustrated in Figure 3. The photographs in Figure 3 show two buildings that were located within one mile of each other in Port Aransas, Texas. The older building had significant damage to roof cover and sheathing, while the newer building appeared to have no damage to these building features. Also, the older building had plywood added to protect the non-impact-rated windows, while the newer building had impact-rated windows; therefore, protection such as plywood is not needed. 4

5 a. A preliminary assessment by a disaster modeling organization indicates that the evolving and statewide building code requirements since Hurricane Andrew in 1992 have made Florida buildings a lot stronger. b. Most jurisdictions in Texas visited by the IBHS team have building code departments and have adopted some edition of the International Building Code (IBC) and International Residential Code (IRC). Figure 3. An older construction with substantial damage (top) and a newer construction with minimal damage (bottom). Both buildings are located within one mile of each other in Port Aransas, Texas. 5

6 6. In areas with no structural damage, roof covering loss on residential structures was common, and conversations with some homeowners in Texas indicated that water intrusion was often problematic. These homes would have benefited from a sealed roof deck. 7. Many FORTIFIED residential properties were surveyed by collaborators in Florida. They reported no structural damage, but loss of roof covering for some properties. The use of a sealed roof deck should have helped to reduce further damages; however, more information would be needed to assess. 8. Vulnerable components and systems for commercial structures included low- and steep-sloped roof covers, metal panel roofs, perimeter edge flashing/fascia and gutters, wall siding, unprotected windows, large commercial doors, and roofmounted equipment. These are the same components addressed in FORTIFIED Commercial standards. 9. Widespread use of shutters and plywood to protect openings was observed and likely helped to reduce the number of substantial structural damages. The use of opening protection was most successful in preventing damages when all windows were protected, not just those in oceanside-facing locations (highest winds and most severe damage in the Hurricane Harvey areas surveyed by the IBHS team occurred on the bay side). 10. Widespread power loss occurred in both storms, due to broken or downed power poles and/or dislodged wire. a. Lack of power infrastructure is likely to be one of the biggest barriers to recovery. b. The use of backup generators (such as those recommended in FORTIFIED Commercial Gold) by businesses with little to no damage would reduce business interruption and help the community recover more quickly. c. Lack of power to all structure types that experienced water intrusion will likely lead to higher losses because of the time required to dry out the structures. 6