Trusses Help Home Outlast Hurricane Michael
Originally published by: Popular Science — October 25, 2018
The following article was produced and published by the source linked to above, who is solely responsible for its content. SBC Magazine is publishing this story to raise awareness of information publicly available online and does not verify the accuracy of the author’s claims. As a consequence, SBC cannot vouch for the validity of any facts, claims or opinions made in the article.
Editor's Note: The section of the article below entitled "Strong Ties" incorrectly attributes the truss plates to Simpson Strong-Tie. As can be seen in the photo, the truss plates on this project were supplied by MiTek.
On October 10, Hurricane Michael spun Category 4 winds around the upper reaches of the Sunshine State. With sustained winds of 155 miles per hour, the tempest was the strongest to ever hit the Florida Panhandle—and the fourth worst to make landfall in the lower United States. Almost every structure at Tyndall Air Force base suffered structural damage. The seaside town of Apalachicola, 54 miles down the coast, saw an 8-foot storm surge. And Mexico Beach, which sits halfway between the two, saw three-quarters of its homes, municipal buildings, and businesses damaged.
But one structure withstood the storm, despite its front step sitting only 150 yards from the wet and windy Gulf of Mexico. Christened the “Sand Palace” by its owners, the blocky beach home survived not by luck or magic, but good design, says Lance Watson, vice president of Southeastern Consulting Engineers and lead engineer on the project. Here’s how—with money and expertise—the crew outmaneuvered Michael, and made this home a model of resilient architecture.
Debris from Hurricane Michael will marr the Mexico Beach landscape for months, but some of that trash was intentional. Engineers designed the walls encircling the ground floor of the three-story house to break away. These wooden slabs looked like any other wall, but bore no load. (That’s what the stilts are for.) When beating waves deliver 20 pounds of pressure per square foot to the storage space, the partitions wash away with the tide.
According to Watson, if the walls had the hardy concrete construction of the upper floors, the material’s structural resistance would have inadvertently increased the pressure of the storm surge, threatening the integrity of the stilts and the living spaces above.
The Sand Palace has great ocean views, but its proximity to the beach places it in a FEMA-designated high velocity flood zone—meaning it’s susceptible to the worst of a hurricane’s frothing waves. To compensate, building code dictates that the house must sit above the projected surge: In this case, that means the two occupied upper floors start 24.4 feet higher than sea level
To support such a spindly structure, engineers had to burrow. Concrete pilings dive 28 feet into the sand. The depth accounts for the total height of the home, with some wiggle room for wind-driven erosion. A hurricane can quickly strip six or more feet of ground cover.
Insulated concrete forms (ICFs) shape the upper floors. To make each 6-inch-thick wall, contractors pour concrete into precast frames and lace it with lengths of horizontal and vertical steel rebar. Two-and-a-half inches of foam on each side provide insulation and strips of polyethylene stagger throughout the block to act like studs. This setup lets contractors anchor sheetrock or siding into the core of the house, rather than superficially slapping them on the outside. Each additional component screws directly into the durable plastic.
No house, even a bulletproof one, is an island. The Sand Palace outlasted this storm, but local utilities did not. It took almost two weeks for homeowners to get back electricity—and only in the form of backup generators. Water pipes, the sewage main, and municipal power lines are still disconnected. “We made it through this one,” says homeowner Russell King. “Whether we make it through the next one, it’s anyone’s guess.”
One fractured window can be the difference between an intact home and a bare concrete slab. When wind finds its way through the seams of a domicile, it can cause a shift in pressure strong enough to rip off a roof.
Each window in the home has three parts: an exterior pane, a small spacer, and a laminated interior pane. “It’s like a glass sandwich,” says Rodney Miller, president of Custom Window Systems, the firm that designed the panes. The exterior sheet may shatter—one in the Sand Palace’s upstairs bathroom did—but the interior laminated sheet is stronger. It’s forged from two panes fused around a synthetic resin called polyvinyl butyral. It’s withstood two hits from a 2-by-4 travelling at 50 feet per second during wind tests. In the worst-case scenario, it will crack like a car windshield, creating a spider-web effect.
“The corners of your house get the most wind pressure,” engineer Watson explains. The gusts act like a crowbar, pushing up against the overhangs. That’s why the owners originally considered building a round home. In the end, however, they opted for a method to reduce pressure on a traditional square building: slimming porches and minimizing awnings.
In the eye of a hurricane, shingles become shrapnel. The Sand Palace’s interlocking 26-gauge steel roof won’t rip apart and keeps a tight seal. Studies have also shown that the “hip roof” layout seen here, with four sloping sides, better withstands pressure from hurricane-force winds than a traditional gable roof, which has just two sloping sides.
Top to bottom, truss connector plates from California-based Simpson Strong-Tie hold the house together. Fangs on the underside of the steel plate secure it to each of the wooden planks in dozens of spots. The joints can withstand a load three times greater than the house itself, a margin that made the engineers confident the home would hold up even in inclement weather. “A lot of design is theoretical,” Watson says. “Simpson, they are not theoretical.”
Building codes and human ingenuity can stand up to Mother Nature—for a price. The owners estimate weatherproofing added 20 percent to the cost of construction, so many Floridians are priced out of resilience—especially since state and federal support is sparse.
True resilience takes place at a community level. Engineers have yet to formally validate this hypothesis, but some media outlets and passersby speculate that the only reason the house behind the Sand Palace is still standing is because its neighbor acted as a shield. The parts the Palace covered are intact, while balcony railing that extended beyond its shadow was ripped free. At the same time, another storm-girded house designed by Southeastern Consulting Engineers suffered structural damage when a nearby domicile flew off its foundation and into the ostensibly impregnable facade.