Engineerinering Designs to Make Houses Hurricane Resistant
- Due to climate change, hurricanes are increasing in severity—a new, higher category may be introduced for ultra-destructive hurricanes.
- Building codes are the baseline defense against hurricane disasters, fortifying homes with off-the-shelf and experimental building materials.
- New experimental materials often focus on modifying concrete and glass, which are the strongest and weakest materials structurally.
Leaving a trail of destruction from Louisiana to New York City, Category 4 Hurricane Ida was exceptional as a cross-regional event, spreading battering winds across the South and flooding rains deep into the mid-Atlantic. With a price tag of just below $100 billion, it's still somehow only the seventh-costliest hurricane since the year 2000, evidence that hurricanes are becoming more severe as climate change takes an increasingly greater toll.
Hurricanes are the costliest weather disaster, and a 2018 Journal of Climate study anticipates an 85% increase in Category 5 storms globally, attributed to climate change. It also predicts there will be an entirely new category needed for ultra-destructive hurricanes. As the oceans and the atmosphere warm, evaporation increases and pulls more water vapor into the atmosphere, to be pelted back to earth through rain and storms. Rising sea levels along the coasts create greater storm surges, pushing floodwaters further inland.
The most damaging hurricanes are three times more frequent than they were 100 years ago, and since 1980, the proportion of major hurricanes (Category 3 or higher) has doubled. These storms bring higher storm surges; accelerate wind speeds more rapidly; and move slower, leaving more time to deposit floodwaters.
What Makes a House Hurricane-Proof?
Hurricanes represent a singular threat to homeowners anywhere near an ocean. Buildings are the most visible marker of an area's resilience after a natural disaster strikes. Surveying the catastrophic damage forces a difficult question: How can it be rebuilt better? It's a question people will be asking more as climate change increases hurricane intensity and rainfall. And certainly, where people build is as important as what they 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.
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. Other post-Andrew changes necessitated tighter regulations on construction materials used in homes and better education and training certification for inspectors and building officials. And indeed, newer structures built to code fared better during Hurricane Irma in 2017.
"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.
It's bold to claim that any home design is completely hurricane-proof, but there are several factors designers and builders consistently look for to make their projects hurricane-resistant. High winds (and the ballistic debris that travels with them) require houses to be built on a structural system that can resist crushing horizontal wind loads. Individual facade and structural components also have to be able to withstand impacts from pieces of airborne houses that didn't clear this first bar. And hurricane-resistant houses must either be elevated above storm surge levels or have a way to relieve the pressure of floodwaters if they make it indoors.
Homebuilder Deltec specializes in hurricane-resistant homes, with a signature look that's a key part of their hurricane hardiness. Each Deltec house (usually only one story) has a round shape that diffuses high winds. Its radial spoke-and-wheel structure stays strong against gusts and waves from every angle. It's tied together with a steel compression ring at the roof's peak, where its pitch is also optimized for wind deflection and lift reduction. These houses are elevated off the ground on pilotis to protect against storm surges, and they use stronger and thicker panelized plywood sheathing on the exterior, with impact-rated doors and windows. This formula has stood up to nearly every hurricane it has encountered.
Components of a Hurricane-Proof House
For traditional wood-frame homes and custom homes, off-the-shelf items can significantly boost hurricane resistance.
Connectors and Ties
"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 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) are cheap to add to new construction, costing only a few dollars each. "It might add 1% to the whole cost," Rimoldi says, adding that it's more expensive to retrofit a house this way. Deltec uses oversized mechanical ties that run the vertical length of the house along each structural member.
Impact Glass
Impact glass, like 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. This storm resistance can result from heat treatments that increase the glass's strength and ensure that, if it does break, it splinters into small pebbles without sharp edges. Laminated glass binds together two or more layers of glass with a thin film of vinyl that holds glass shards together if a window breaks.
Spray-Foam Adhesive
Rimoldi says new roof-attachment methods can add strength, and spray-foam adhesives (applied on the inside of the house's roof, doubling as insulation) are rated for higher wind speeds. This adhesive insulation acts like glue, strengthening the connects of structural members in your home. It's also water-resistant and can withstand floodwaters for days without getting waterlogged.
Flood Vents
For homes that aren't elevated, flood vents installed at the ground level of houses allow water into the home, preventing the tremendous pressure of rising floodwater from pushing a house off its foundation.
Next-Gen Hurricane-Proof Materials
Experimental materials can aid in hurricane sturdiness, which becomes an essential mandate as hurricanes get stronger, accelerate more rapidly, and drop more rain. Innovations in this area have largely focused on the strongest building materials (concrete) and the weakest (glass)—though advances have also been made for wood and composite materials.
Bendable Glass and Spinel Ceramic
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 micro-fissures to allow it to bend without shattering. These jigsaw-shaped engravings stop fractures from spreading, making the glass 200 times stronger than standard glass. The glass masters at Corning are also developing bendable glass, which is likely to see heavy action in foldable smartphones. And scientists at the US Naval Research Laboratory are developing an ultrahard ceramic "transparent armor" material called spinel, which has opacity levels similar to glass.
Ultra-High-Performance Concrete (UHPC)
One of the most promising new materials on the market is ultra-high-performance concrete (UHPC). Developed by the US Army for nuclear blast shelters, Cor-Tuf UHPC is 10 times stronger than traditional concrete; lasts three times as long; and is made from agricultural byproducts, calcium mineral, and water. More established is the UHPC made for use in the United States by Holcim under the name Ductal. This 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 is on full display at the Perez Art Museum Miami, a seemingly hurricane-proof building that withstood Hurricane Irma with no damage. For the museum, UHPC was used in 16-foot-tall, 5.5-inch-thick mullions that taper down to 2 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 10 times more expensive than standard concrete, so it "wouldn't be cost-effective in the majority of normal construction," he says, 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.
Engineered Cementitious Composite (ECC)
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 says, 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? The MIT Concrete Sustainability Hub (CSHub) is asking that question. 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.
3D-Printed Concrete
Texas-based construction -technology company Icon has developed a hurricane-wind and disaster-resistant concrete-printed house template that uses a proprietary concrete blend and a massive printing test bed to create homes that can stand up to nearly anything. The company's adjustable-width Vulcan test bed can print concrete walls up to 28 feet long and 8.5 feet high, good for a 2,000-square-foot house. Controlled by a tablet, the Vulcan moves fast, laying down a 1-inch-tall, 2-inch-wide bead of its proprietary Lavacrete at 5–7 inches per second. This material has a compressive strength of 6,000 psi, higher than most concrete.
Mass Timber and Cross-Laminated Timber (CLT)
A company in the Bahamas is looking to mass timber in general and cross-laminated timber (CLT) specifically to produce hurricane-resistant buildings. Offsite CLT Construction designs and builds businesses, offices, apartments, and single-family beachside homes with CLT, built specifically to withstand Category 5 hurricanes. The designs are meant to withstand hurricane-force winds of more than 200 mph, per the records broken by Hurricane Dorian in 2019, the strongest storm on record for the Bahamas. With sustained winds of 185 mph (which peaked at just over 200 mph), it's tied for the strongest winds at landfall in the Atlantic Ocean and is considered the worst disaster in the nation's history.
"One of the benefits of CLT is that it behaves very well when dealing with [horizontal] shear loads similar to those found in earthquakes or in a hurricane," says Offisite CLT's Juan Cat Diaz. Another benefit is that a standard timber-frame building of similar strength would require many more fasteners, brackets, walls with more studs, and short spans between posts, he says.
The Cost of Hurricane-Proof Housing
"People are used to thinking about a payback for a more energy-efficient refrigerator," CSHub's 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 most contexts.
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 hurricane-resistant buildings is an efficient use of money and 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.
How Climate Change Impacts Home Construction
Although building codes in some places have evolved, they neglect the many existing homes built before code changes. The ravages of climate change and ever-stronger and frequent Category 5 hurricanes can't be addressed entirely at the building scale, and new materials and design innovations will have to be applied en masse to make communities truly resilient. As the debate about federal government investment in climate-change resilience sputters on, homeowners, builders, and local municipalities are left to play catch-up with a worsening climate trajectory, rebuilding for today's disaster knowing that tomorrow's may well be worse.
This article has been updated. It originally published in November 2017.
Zach Mortice is an architectural journalist based in Chicago. Follow @zachmortice on Twitter and Instagram.
Engineerinering Designs to Make Houses Hurricane Resistant
Source: https://redshift.autodesk.com/hurricane-proof-construction-methods-can-save-buildings-communities/
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