How Do Storm Shelters Stand up to Extreme Winds?

Storm shelters are designed to protect their occupants from all kinds of catastrophic weather events, including blizzards, tropical storms, tornadoes and hurricanes. All these storms have one thing in common: strong winds. Here’s an in-depth explanation of how different types of shelters stand up to extreme winds.

How Common Are High-Wind Events?

High-wind events are more common than most people realize — especially tornadoes. A surprising amount of the United States faces a moderate to high risk of a tornado strike, including most of the Midwest and Southeast. Some states get hundreds of these storms every year. Tornadoes only take a few hours to develop, leaving communities little time to react.

Communities within a few hundred miles of the East Coast and the Gulf of Mexico face a constant risk of hurricane and tropical storm damage. These events can take just a few days to develop, so evacuation might not be an option. States farther north that get lots of snowfall can experience a handful of debilitating blizzards every winter.

It’s also worth noting that extreme weather events are becoming more frequent and severe due to the growing effects of climate change. The country is at a greater risk of high-wind weather, which continues to increase.

Lucky individuals will only experience minor exterior damage to their homes. In the worst-case scenario, entire houses can get carried away by strong winds, never to be seen again. Nobody wants to be trapped inside if that happens. A storm shelter prevents such a disaster, keeping everyone and everything inside safe from the outside world.

Storm Shelter Building Regulations

The International Code Council and American National Standards Institute are the main governing bodies that set global standards for storm shelter construction. The 2020 ICC-500 is the latest criteria, including design requirements for the main wind-resisting structural system, lighting, sanitation, ventilation, fire safety and floor space.

An ICC-approved shelter must meet the following criteria when it comes to wind resistance:

• Walls and roofs must have adequate anchorage to resist overturning and uplift.

• Walls, ceilings, doors and windows must withstand design wind pressures and resist penetration by windborne objects and falling debris.

• Connections between building elements must withstand design wind pressures.

The term “design wind pressures” refers to the strongest potential winds the shelter might face, which depends on its location. Homeowners who want to build a storm shelter must know their local wind zone. All residential properties in the U.S. must have a data plate indicating the building’s wind zone.

Most residences fall into Zone 1, requiring homes to resist wind speeds up to 70 mph that often occur in severe storms. Zone 2 houses must withstand up to 100 mph and typically lie within a high-risk hurricane or tornado zone. Zone 3 applies to residential properties that must resist wind speeds up to 110 mph.

Homeowners should also take their local geographic features into account. Some landmarks are more exposed to strong winds than others. Cities and woodlands are the least vulnerable because of their tightly packed obstructions, while grasslands and areas near large bodies of water are much more exposed.

Every storm shelter in the U.S. must also meet all requirements set forth by the Federal Emergency Management Agency (FEMA) to ensure its structural integrity. The American Society of Civil Engineers provides additional documentation for wind loads and other structural guidelines. These organizations work together to enforce specially engineered shelter designs.

Wind-Resistant Storm Shelter Materials

Concrete masonry is the ICC and FEMA’s preferred material for storm shelters because it provides a continuous load path from roof to foundation. Connecting concrete roof slabs to the shelter’s walls with reinforcing bars is simple construction. It’s the strongest material against winds, withstanding up to 250 mph in tests conducted at Texas Tech University.

Although the ICC and FEMA prefer concrete masonry, other viable materials exist. For example, quarter-inch carbon plate steel is popular for many U.S. shelters because it’s two times thicker than federal requirements. Builders can easily adapt steel plates to projects, including small residential bunkers and large community shelters.

Steel plates also provide the opportunity to apply an industrial exterior coating that improves the shelter’s longevity. The coating protects against corrosion, cracks, moisture and mold, helping the inner shell last for generations. This feature is a huge advantage for storm shelters, bomb shelters and survival bunkers designed for long-term residency.

Types of Storm Shelters

Storm shelters come in many shapes and sizes, but they all fall under two categories — underground and aboveground. Both types offer adequate protection against extreme winds but have some advantages and disadvantages.

Underground Storm Shelters

Underground storm shelters provide the greatest protection from outside elements as long as they can remain dry when surrounded by moist soil. Soil is another protective layer from strong winds and flying debris, but it can also get oversaturated with moisture and damage the shelter. This factor is another reason nonporous steel is a better alternative to porous concrete.

Of course, underground shelters are also more effective against high-wind events because the wind can’t carry them away. An aboveground shelter connected to the house could get carried away with the rest of the structure. Moreover, subterranean structures face a lower risk of getting hit with flying debris. Storms glide right over them with minimal disturbance.

However, although underground shelters can’t get carried away by winds, occupants can get trapped inside if the entrance is blocked during the storm. That’s why they are usually designed for long-term residency. They include emergency phones, food storage compartments, and complete bathrooms and kitchens.

Versatility is a huge advantage of underground shelters. They allow for numerous upgrades and customizations to the interior, including secondary exits and wheelchair accessibility. Floor plans are also completely customizable, allowing designers to maximize the shelter’s structural integrity within its unique environment.

Aboveground Storm Shelters

Aboveground shelters might not offer as much protection as their underground counterparts, but they’re still effective against strong winds. FEMA suggests staging residential storm shelters in a basement or interior room on the first floor. The location must have a floor extending to the ground or sit on top of a concrete slab-on-grade foundation.

Aboveground shelters with a solid foundation can be as strong as underground ones. They consist of the same primary material — concrete masonry or plate steel — and are easier to access than subterranean bunkers. Everyone inside the building can reach the shelter at a moment’s notice if a tornado suddenly strikes.

Building an aboveground shelter for communal areas, such as schools and large office complexes, is more practical and cost-effective. These buildings need a centralized location that everyone can quickly access during an active storm. Aboveground shelters are more accessible and can fit into more places than underground bunkers.

Although aboveground shelters are naturally more vulnerable and have some design limitations, they’re still viable options for wind protection. Their accessibility, affordability and flexible location sites make them even better than subterranean bunkers in some scenarios. Still, both options will serve well when people need emergency shelter from extreme weather.

Strong Winds Don’t Stand a Chance

Strong winds won’t stand a chance against an underground or aboveground shelter. As long as the bunker meets all federal building requirements and utilizes durable materials, it will withstand the heaviest winds from tornadoes, hurricanes and other extreme weather events.

Author Bio

Jack Shaw is an outdoorsman and prepper who’s spent much of his life trying to understand the best ways to navigate and survive the world around him. Currently he serves as the senior writer for Modded, a men’s lifestyle magazine.