The Insurance Institute for Business & Home Safety (IBHS) has conducted a full-scale research test program of how wind-driven water, such as that occurring during hurricanes, penetrates openings in residential roof systems.

“Wind-driven rain that gets into a house through openings in the roof can collapse ceilings and cause extensive damage to interior finishes, furnishings, and other family possessions,” said Julie Rochman, president & CEO at IBHS. “The testing conducted by our engineers clearly demonstrated that water penetration during hurricanes could be substantially reduced by sealing the roof deck seams.”

For new construction or re-roofing, roof deck seams can be sealed from the exterior using a modified bitumen tape. For retrofitting when the roof cover is not replaced, homeowners can seal the roof deck seams from the inside with a closed-cell foam spray adhesive.

IBHS researchers built a 1,300-square foot, single-story duplex test building with construction features common in many coastal and inland areas of the Atlantic and Gulf Coast states with hurricane exposure. The interior of the duplex was furnished. Both sides of the duplex roof were identical, with the critical exception of using modified bitumen tape to seal the between-sheathing joints and gaps on one side of the roof.

The  building was placed inside a 21,000-square foot test chamber and subjected to several individual test sequences involving high-speed, multi-directional, gusty winds and prolonged exposure to the typical amount of rain during a hurricane, delivered at a rate of up to eight inches per hour. Video footage of the interior of both sides of the building filmed during the test showed water entering the side with the unsealed roof deck, streaming off of light fixtures and ceiling fans. Approximately 30 minutes after the completion of the test, portions of the ceiling on the unsealed side began to collapse.

“In the real world, a family would be uprooted from the home without the sealed roof deck, potentially for months while repairs were made,” said Dr. Anne Cope, IBHS research director. “However, a family living in the home with the sealed roof deck could probably stay in the home while repairs were made, and if they did have to leave, then they would likely be able to return to the home much sooner.”

Following the test, IBHS brought in a trained claims adjuster to estimate the amount of damage each house suffered. He assessed the damage to the front three rooms on both sides of the duplex, including the kitchen, dining room, and family room. During a hurricane or high wind event, winds generally come from a relatively small range of directions after aroof cover has blown off, so damaged is usually confined to one area of a house.

According to the adjuster’s report, estimated damage on the unsealed side totaled nearly $17,000, while estimated damage on the sealed side totaled approximately $5,400. Of particular note is that the furniture in the side with the unsealed roof deck had to be replaced, while the furnishings in the side with the sealed roof deck only had to be cleaned.

“Sealing the roof deck can significantly strengthen this critical part of a home and reduce the chances of a catastrophic loss due to water damage when the roof covering is compromised or blown off entirely during a high-wind event,” Cope said.

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