Redshift Ι Nov. 9, 2017
The four hurricanes that slammed into heavily populated areas from the Caribbean to Texas this summer are inching toward a half-trillion-dollar price tag in damages—to say nothing of the work and wages missed by shutting down entire cities. Buildings are the most visible marker of a place’s resilience after a disaster strikes. Surveying the catastrophic damage forces a difficult question: How can it be rebuilt better?
It’s a question people will be asking as climate change contributes to hurricanes’ increasing intensity and rainfall. And certainly, where you build is as important as what you build. But new materials, in a wide range of experimental and off-the-shelf options, can help fortify buildings against a hurricane’s suite of hazards: winds, flying debris, and flooding from rain or storm surges. Understanding how built environments can coexist with worsening hurricanes will require mapping the most useful, and cost-effective, applications for hurricane-proof building materials and technology.
Building codes are the baseline defense against hurricane damage. Improved building codes in Florida (the most stringent in the nation) after 1992’s Hurricane Andrew required installing impact windows, using stronger ties between roofs and walls, and securing roof shingles with nails instead of staples, according to the Wall Street Journal. And indeed, newer buildings built to code fared better during Hurricane Irma.
“We found that a lot of places that don’t have an up-to-date building code are often where you see the most impacts from even the most minor storms,” says Michael Rimoldi, the senior vice president of education and technical programs at the Federal Alliance for Safe Homes (FLASH), which advises FEMA on building hurricane resistance.
The Ties That Bind
For traditional wood-frame homes in particular, off-the-shelf items can significantly boost hurricane resistance. Impact glass, such as the kind used in cars, won’t shatter like standard glass. When windows burst from high winds, the house can pressurize as wind rushes in, popping off the roof and freeing dangerous debris. Rimoldi says new roof attachment methods can add strength, and spray-foam adhesives (which are applied on the inside of the house’s roof and double as insulation) are rated for higher wind speeds. To deal with flooding, hydrostatic vents allow water into the home but stop floodwaters from accumulating, potentially degrading its walls and foundation.
“In the traditional wood-frame home, [it’s] how it’s all put together,” Rimoldi says. “All of the components, from the top of the roof down to the foundation, are tied together by mechanical connectors. You can build a wood-frame home that’s just as strong as anything else, as long as you ensure that all the walls are tied together properly, they’re tied to the roof properly, and the roof and walls are tied to the foundation properly.”
Specialty metal connectors for this task (like the sort made by Simpson Strong-Tie) can cost only few dollars each, so they’re cheap to add to new construction. “It might add one percent to the whole cost,” Rimoldi says—though it’s more expensive to retrofit a house this way.
Experimental materials might aid in hurricane sturdiness. Several research efforts are focused on finding glass prototypes that increase the resilience of impact glass. Researchers at McGill University are studying bendable glass, which relies on engraved “microfissures” to allow it to bend without shattering. These jigsaw-shaped engravings stop fractures from spreading, making the glass 200 times stronger than standard glass. Scientists at the US Naval Research Laboratory are developing an ultra-hard ceramic “transparent armor” material called Spinel, which has opacity levels similar to glass.
One of the most promising new materials on the market is ultra-high-performance concrete (UHPC). Made for use in the United States by LarfargeHolcim under the name Ductal, UHPC can bend and give, yet is six times stronger than regular concrete. It’s made of very fine aggregate, often from recycled materials (fly ash, silica fume). The addition of carbon metallic or polyvinyl alcohol fibers allows the material to bend and carry loads even after some cracking has occurred.
UHPC has been used sparingly in the United States over the past decade or so. However, it’s on full display at one high-profile project: Herzog and DeMeuron’s Perez Art Museum Miami, which withstood Hurricane Irma with no damage. Here, UHPC was used in 16-foot-tall, 5 1/2-inch-thick mullions that taper down to two inches while still supporting the building’s curtain wall.
But UHPC can’t simply be substituted for regular concrete in every case. “It’s expensive, and you have to get a license to buy it and use it,” says Robert Nordling, project manager for John Moriarty & Associates, which built the Perez museum. With these extra fees, the material is eight to ten times more expensive than standard concrete, so it “wouldn’t be cost-effective in the majority of normal construction,” especially on smaller, lower-budget projects. However, UHPC’s strength means that, often, less material is needed compared to standard concrete, making it more efficient by weight and expense.
Victor Li, an engineering professor at the University of Michigan, has been developing a variant of concrete called engineered cementitious composite (ECC) that emphasizes ductility more than sheer strength. “If Ductal is to hard rock, then ECC is to malleable steel,” Li says. The material has high energy-absorption capability against impact and earthquake loads, and is being adopted in full-scale buildings, bridges, and roadways. “For example, the 60-story Kitahama building in Osaka uses ECC in the building core for earthquake resistance,” Li explains, adding that the building has a lowered install cost and larger usable floor area “when compared with previous designs that don’t use ECC but use other anti-seismic approaches.”
ECC is two to three times more expensive than standard concrete. With that kind of premium, where, and for what, does it make economic sense to build with it? That’s one question being asked by the MIT Concrete Sustainability Hub (CSHub). Instead of developing more materials and building systems, the largest shift in material analysis for disaster resilience is determining which systems are cost-effective in which locations, says CSHub Executive Director Jeremy Gregory.
“People are used to thinking about a payback for a more energy-efficient refrigerator,” Gregory says. “They know they have a higher initial cost, but lower operating costs. But when it comes to hazard-related damage, it’s a trickier thing to do.” Asking consumers to bank on the worst-case scenario to justify extra expenses is a recipe for under-preparation in almost any context.
So Gregory’s project, the Break-Even Mitigation Percentage (BEMP), looks at hurricane damage likelihood over 50 years in a given location, calculating the amount of damage predicted, as well as the building type and the way it was constructed. It uses this data to determine whether making these structures hurricane-resistant is an efficient use of money, and to calculate how soon the anticipated cost savings in an avoidance of hurricane damage will pay back the initial expense.
The BEMP will be expanded to include building materials’ carbon footprint and other environmental impacts. It might seem like accounting for a natural disaster is a discrete and singular cost-benefit analysis, but in this way, it’s really an overall measure of sustainability. With this kind of analysis, planners will know which areas climate change may make dangerously uninhabitable, and which areas can persist with stronger buildings using these materials and techniques. The BEMP could likely become a field guide for construction companies looking to apply hurricane-resistant materials and methods across a wide range of vulnerable shorelines, matching careful economics with the deep-seated desire to rebuild.