Hazard Mitigation Assistance e-brief
USVI Mitigated Roofs Remain Strong After 20 Years and Hurricanes Irma, Maria
by Hazard Mitigation Assistance
It was mid-hurricane season 1995 in the U.S. Virgin Islands. No storm had hit the region since Hugo seven years prior, but in the first weeks of September, Hurricane Luis made landfall. A week later, Hurricane Marilyn, a Category 3 storm, followed in its wake.
Marilyn had a smaller diameter than Luis but wreaked much more havoc. Wind gusts of 129 miles per hour were recorded, storm tides measured six to seven feet high and rainfall was reported to be as much as 10 inches in some areas.
In total, Marilyn was responsible for eight deaths, the loss or damage of 21,000 homes, impairment of 5,800 utility poles and destruction of two sewer plants. In St. Thomas, the storm rendered a desalinization plant inoperative and damaged approximately 75 percent of the residences. As a result FEMA’s USVI damage estimates came in at $2.1 billion.
While most of the affected dwellings were either insured or eligible for recovery efforts through assistance programs, a small percentage were not. As a result, a year after Marilyn, then- Governor of St. Thomas, Roy L. Schneider, appealed to FEMA for aid repairing or replacing roofs for approximately 350 homes on the islands.
Through FEMA’s Hazard Mitigation Grant Program, slightly over $30 million was granted to the USVI, providing the Territory with resources for design, construction, formal construction management oversight, and quality assurance and quality control. The grant also funded a vital part of the regions’ post-disaster mitigation plan — the Home Protection Roofing Program (HPRP).
One of the key components of the HPRP was to address the issue of poorly attached roofs which could easily be torn from houses by wind. FEMA collaborated with local USVI officials to develop two HPRP design solutions: improving the attachment of corrugated metal roofs to joists or beams, or building roofs by applying a liquid membrane over plywood.
Another of the HPRP’s enhancements involved homes’ gutter systems. At the time of Marilyn, most homes had external gutters that drained rainwater into cisterns. The water could later be used as gray water for general household activities or treated to become drinking water.
Unfortunately, Hurricane Marilyn tore many external gutters from homes, which then became damaging, flying debris and whose absence prevented cisterns from recharging. During the HPRP design specification process, it was determined that roofs should be reconstructed with pieces of lumber at the edges to dam rainwater and drain it into downspouts. This created integral gutters and reduced the hazard caused by external gutters.
More than 20 years later, in the wake of Irma and Maria, a 12-person mitigation team from FEMA’s Joint Field Office in the USVI, returned to the islands. One of their goals was to assess a sample of St. Thomas HPRP homes to determine how the roofs fared.
The result: no structural damage was observed. Additionally, the team visited approximately 75 homes containing integral gutters. None of them dislodged and flew away.
“This program was a success,” said Jonathan Westcott, Civil Engineer and member of the U.S. Virgin Islands Mitigation Assessment Team (MAT).
In fact, one homeowner whose HPRP-improved home performed well during the hurricanes invited her two adult sons to move in with her after their homes were destroyed during the storm. When a mitigation specialist asked about her roof, she is said to have responded “The Governor gave me my roof and I’m very happy for it.”
“[We’re] really pleased with the performance we’re seeing out of these buildings,” said Tom Smith, member of the current USVI MAT and one of the original architects who developed roof modification design specifications under the HPRP.
On the heel of Hurricanes Irma and Maria USVI wrap-up activities, mitigation specialists are taking time to reflect on past projects, such as the HPRP, to assess how its successes may be used to recover from recent devastation.
Although the HPRP design specifications did not account for topographic winds (for example, increased wind speeds due to sudden geographical changes such as a cliff), HPRP roofs still performed well during the storms because of their robust design and details.
Future construction proposals will use increased wind load criterion based on research conducted since Hurricane Marilyn. Additionally, although there is no requirement for integral gutters in the current building code, their outstanding performance during the 2017 Hurricane Season led Mitigation Subject Matter Experts to recommend them for rebuilding efforts.
Regardless of the HPRP’s successes, some MAT members consider the greatest post-Marilyn accomplishment to be advancements in the USVI building code. Prior to Marilyn, the code for wind resistance was weak, but following FEMA’s post-storm recommendation, USVI adopted the 1994 Uniform Building Code which provided significantly more wind resistance requirements. As a result, although Hurricanes Irma and Maria were more severe than Marilyn, structures that were repaired or constructed to the 1994 codes showed far less roof damage during Hurricanes Irma and Maria than structures built pre-1994.
Interested in learning more? Visit the FEMA USVI Facebook page for more information on the USVI recovery process.
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