If you’ve ever built a roof using Huber Zip System sheathing, you know the drill: You lay the sheets down, nail them off, then seal every joint using that black Zip tape. And chances are you’ve seen that system keep the water out of a house during construction, even before the roofing is installed. It’s reason to have confidence in the sheathing to protect the house if there’s a roofing leak later.
But you’ve probably never had a house under construction go through a hurricane, and you may have wondered whether that roof sheathing by itself would keep the house dry during 105-mph winds and blinding sheets of rain, in case the shingles were lost. Well, I’m here to tell you that it would. That’s what I saw in a recent trip to the Insurance Institute for Building & Home Safety’s Research Center down in Chester County, South Carolina.
The Research Center’s wind tunnel facility is a one-of-a-kind laboratory. It’s big enough to hold an entire house and powerful enough to put that house to the test: A bank of 105 fans with 350-horsepower motors is capable of making winds up to 130 mph, and the plumbing can produce rain conditions typical of a hurricane eyewall. (The facility can also replicate hailstorms and wildfire ember showers.)
For this demonstration, a full-scale house sheathed with Zip System’s characteristic red sheathing was hit with a replication of 30 minutes of Hurricane Florence, which struck North Carolina in mid-September of 2018 as a Category 1 storm, dumping as much as 35 inches of rain. After watching the tempest in a teapot for 30 minutes, the spectators had a chance to inspect the roof from the inside. Sure enough, the underside of the sheathing was bone-dry, with the exception of one small trickle of water. After that, the visitors were allowed to stay in the house through another 15 minutes of the storm, as man-made wind and rain buffeted the building in a vivid demonstration of the power of nature under controlled conditions.
IBHS invited a handful of executives from Huber, makers of Zip System, to view the demonstration. But Huber had no involvement in the experiment itself: IBHS purchased the panels and tape on the open market, and constructed the building and assembled the roof themselves. The Huber team, it’s safe to say, was not surprised by the outcome (they had fully expected their product to stand up to the simulated storm).
IBHS’ above-code “Fortified” standard calls for taping the roof sheathing seams as one method of making the roof weather-tight in case the shingles blow off. Zip System is a natural for that arrangement. But the IBHS spec also calls for one layer of roofing underlayment on top of the taped sheathed deck. With its own integrated weather-resistive barrier, Zip System would seem to make that step unnecessary. And indeed, the wind-tunnel test indicates that Zip System on its own can keep a roof dry even with no shingles installed.
The Research Center’s chief engineer, Anne Cope, https://ibhs.org/team/anne-cope/ finds the results convincing. “The Zip System demonstrates that it does a fantastic job of keeping Mother Nature out when terrible storms come your way,” she said.
Cope’s personal experience puts the significance of her lab work into perspective. In 2004, she had the luck to experience just the problem a sealed roof deck is designed to address. “The hurricane season of 2004 was particularly brutal to the state of Florida,” she remembers. “And my parents, who lived in Central Florida, were right in the middle of that season of hurricanes. They live in Winterhaven, which is a beautiful town in central Florida, and if you draw the tracks of Charlie, Francis, and Jeanne, all three tracks went through Winterhaven, Florida, in Polk County, that particular year.”
When Hurricane Jeanne came through Winterhaven, Cope had evacuated from her own home in Melbourne, Florida, and was in her parent’s home. “I was in the house listening to the shingles get torn off the roof overnight,” she recalls. “And I’ll tell you, if you have never experienced that, that is not a good sound. You can hear them: ‘Pow,’ ripping off. ‘Pow!’ Ripping off.”
When there was enough light to see in the morning, Cope remembers, “I went out there in the kitchen and the water was coming in. The water was dripping around the lights in the kitchen and spilling out onto the countertops and onto the floor. The ceiling was starting to bow. I went to the utility room and grabbed a broom, and using the handle of the broom I made holes in the ceiling to let the water through, because I was worried that the ceiling would collapse without that effort.”
“And the only thing that happened to my parents’ house was the loss of asphalt shingles,” Cope observes. “There was no other damage to the structure at all. But because the roofing was compromised, the water came pouring in. And my parents were in a small FEMA trailer in their driveway for months, waiting for the house to get put back together so they could move back into it.”
“If they had had a sealed roof deck,” says Cope, “sure, they would have still had to replace the roof because the shingles were damaged. But the water would not have come in. They could have stayed in the house and not had that terrible experience of remodeling the entire kitchen because of water damage and mold.”
It’s worth noting that the 105-mph wind speeds in the IBHS demonstration are well below what a major hurricane could bring near the coast at landfall. But Cope says that this velocity of wind is enough to do plenty of damage to a roof. “We see a lot of shingle damage at those lower wind speeds,” she says. “Hurricane Florence caused a lot of damage in the Carolinas. Shingles are rated to wind speeds of about 150 mph, but we see time and time again that shingles are lost, particularly when they are older, at tropical storm wind speeds and Category 1 hurricane wind speeds. We see a lot of roof damage.”
The IBHS Fortified spec is an above-code program. But based partly on the IBHS Research Center’s research, the sealed roof deck is finding its way into the building code. “The sealed roof deck will be part of the Florida Building Code in 2021,” says Cope, “and sealed roof deck will be part of the I-codes in the high wind areas, in areas where the design wind speed is greater than 140 miles an hour, in 2021. And so we are moving in that direction.”
