Designing for Disaster in an Increasingly Dangerous World

The worst damage from hurricanes often occurs after the storm hits. Retained rainfall in swollen rivers and lakes causes rampant flooding. In North Carolina, the aftershocks of hurricanes Florence, Matthew, and Michael have inundated entire communities, causing billions of dollars in damages. The state has responded by publishing better flood maps, dispensing information about how to protect homes from rising waters, and even paying to move or elevate at-risk homes.

Another common precaution: installing foundation vents that allow flood water to flow through a home rather than pool around, relieving pressure on walls and basement windows. FEMA recommends installing inexpensive backflow valves in homes that might be subject to flooding; it prefers gate valves over flap valves since they provide a better seal against flood pressure. 

Storm drains couldn’t handle the flood in Houston and surrounding Harris County, which were hit with three 500-year storms in three years. In response, the city has abandoned 100-year-floodplain guideposts in favor of the 500-year plain as a standard for regulatory purposes, building flood retention ponds, and upgrading the dam on Lake Houston. But that may not be enough, according to the Baker Institute, which stresses the need to acknowledge the real risk of flooding, install markers and signs, develop a flood-warning system, and perhaps even buy back homes in flood-prone areas.

Hurricanes and tornadoes aren’t the only threat to Houston. According to a NOAA report, major coastal cities can expect sea levels to rise by up to a foot within the next 25 years. By 2050, moderate flooding, which is already a major problem in cities such as Annapolis, Maryland, can be expected to occur 10 times more frequently. Rising seas pose an even greater threat to cities such as New Orleans, San Francisco, and Norfolk, Virginia, that are sinking anyway. San Francisco decreed that all new construction projects show a plan for mitigating the impact of rising seawater. New York City plans to spend $20 billion to shore up its defenses. Miami Beach is raising its streets by 2 feet.

A recent University of Vermont study concluded that while Americans are migrating away from coastal cities subject to heat waves and hurricanes, they are moving to forested areas threatened by wildfire. Once again, the number of properties at risk from forest fires may be greater than federal fire maps would have you believe. First Street recently identified 80 million properties at risk of wildfire. It considered local information about the age of properties and how they were built. The group forecasts that the number of buildings annually lost to fire will double from 17,000 within 30 years “due to climate change alone.”

A patchwork quilt of wildfire codes covers the nation. Only California, Nevada, Utah, and Pennsylvania have statewide wildfire codes, though an additional eight states publish wildfire-mitigation guidelines. Colorado last year set a path to enact a statewide wildfire-resistant building code by July 2025. Washington, on the other hand, scrapped new wildfire protection rules for buildings on the day they were supposed to take effect. The state’s builders argued that new code protections would add to the cost of a home and were better left to local governments. 

One study suggests that building a prototypical home to the Wildland Urban Interface Code (WUI) can cost less. But there’s a big hitch: the analysis assumes a switch from cedar to fiber cement siding, which to some people may defeat the purpose of having a home in the woods. The material change, however, will pay for a better roof, stronger windows and doors, and fire-retardant landscaping close to the house. (The study excludes the cost of fire-resistant landscaping throughout the yard, which can be a considerable added cost.)

Wildfire codes focus on designing a fire-resistant exterior. The idea is to cover every nook and cranny because fire seeks out the weakest link: a flimsy attic vent, an unprotected eave, or a weak window. Small defenses can make a difference. Consider the case of this home in the mountains outside Sonoma overlooking the wine country directly in the path of the Norrobom Fire, part of a system of 21 Northern California wildfires in 2017. Yet this home, built with plaster-covered straw bales, survived largely unscathed.

Architects Anni Tilt and David Arkin designed the house to meet the WUI, which calls for establishing a defensible perimeter. Concrete porches and decks provide a first line of defense against the fire spread. Fire encounters plaster when it meets the house at ground level. Inch-thick redwood and cedar on exterior walls naturally resists fire. Lava outcroppings around the yard—the house rests in a bowl of sorts—probably also kept fire away. In any event, the house sustained minimal fire damage, most caused by leaves trapped in grates required by the county.

The problem is that fires keep showing up in unexpected places, like suburbs miles from forests, as was the case with the Norrobom Fire, which leapt into Santa Rosa subdivisions. Yet the code provisions appear to be making a difference. One analysis of damage from the 2018 Paradise, California, fire found that slightly more than half of the 350 single-family homes built to the new fire code escaped damage. But of the 12,100 homes built before then, only 18% were undamaged.

Building homes to prevent mudslides and other types of erosion may be the priciest proposition of all; homes may require metal or concrete pillars driven deep into the ground. We got a reminder of the danger of moving earth earlier in the year when Los Angeles saw 562 mudslides and 15 red-tagged homes. The most vulnerable areas are hillsides charred by wildfires. In 2018, a debris flow in Montecito, near Santa Barbara, destroyed or damaged hundreds of homes and killed 23 people.

The slide spared the house on the cover of my book from damage, even though it’s on a cliff overlooking the Pacific. The home was built on metal piers, driven 10 to 30 feet into stable bedrock, an expensive but necessary provision. The architect set back the home 12 feet from the cliff to provide 100 years of erosion protection. A retaining wall in the backyard runs around the porch, protecting the house from runoff. 

The situation has clearly worsened since my book’s publication. Even as severe weather grows more common and storm damage grows, few communities have adopted tougher code protection. It remains incumbent on homeowners to figure out whether their home would be in jeopardy and work with professionals on how best to protect it. The good news—if any news regarding this subject is good—is that methods for protecting homes from natural disasters have not changed much in five years. In fact, professionals are growing more familiar with these now-vital techniques, which should eventually lower their cost.