• Thomas Campbell, president and structural engineer at Alpha Consulting Engineers
• Andrew Dziak, structural project manager at LPA Design Studio
• Mike Miller, sales engineer at Vulcraft
• Mathew Sleiter, senior project manager at L.A. Fuess Partners
• Lloyd Smith, design engineer at New Millennium
• Santosh Yadav, design engineer at New Millennium

Material Selection and Geographic Considerations

When thinking of constructing a new storm shelter, geographic location does affect how the shelter is designed and what material is selected. “In Texas we do a lot more concrete masonry units (CMU) with composite roof-level shelters that meet the ICC 500 requirements,” says Andrew Dziak. “Closer to the coastal regions you may be doing more tilt-wall or CMU shelters.” Santosh Yadav of New Millennium adds that coastal locations require special attention to material durability. He says, “The material selection, if it’s in the coastal area, should be corrosion- resistant. If it’s inland there’s less chance of saltwater impact on those materials, so that’s another thing that needs to be considered.”

Design Approaches and Construction Methods

The most common construction method for storm shelters involves composite joists with concrete topping. “When we get into structures that have clearance limits and longer spans, composite joists are the way to go,” explains Thomas Campbell. “The joists allow us to pass ducts through them, which works better for longer spans. When we get into shorter spans in structures that don’t have those clearance limits, occasionally we’ll use beams. But for spans over 40 feet, joists are typically the best solution.”

And when airborne debris missiles come into play, many agreed that concrete topping versus a typical deck roof was the better option to use. Mike Miller, a sales engineer at Vulcraft, also points out the economic advantages of this approach. “In my experience it’s more economical to have more weight. Even if that makes the downward loads heavier, it more than offsets the cost of designing for the full uplift.”

The importance of redundancy in design was also highlighted by Lloyd Smith. “Using the concrete to counteract the wind loads like we’ve been talking about of course can build redundancy into it because it’s designed not to be destroyed, it is designed to not give way to anything. It’s supposed to withstand and not be destroyed, so the connections are important for that resiliency. Joists can use various kinds of connections to be able to tie into the walls and create some resiliency.”

In many places, school gymnasiums have emerged as the preferred location for storm shelters due to their practicality as a gathering point. They can be chaperoned easily, everybody can see everyone and it’s a lot easier to get the restrooms in that space. Typically gymnasiums have adjacent locker rooms so they can encompass that into the gymnasium storm shelter. This place is also a natural area to put a windowless or close to windowless room, whereas designers aren’t going to look to make a classroom nearly windowless.

Future Trends and Challenges

The future of storm shelter design is likely to see increased focus on cost-effectiveness without compromising safety. Our experts also mentioned there being more emphasis on performance-based design and more sophisticated modeling tools when budget pressures push on the projects. “With today’s budget, a big thing is right-sizing the shelter and having more that needs to be done sooner,” Thomas emphasizes. “Budgets are very tight. But we’re just trying to make sure you have the right size shelter for what you really need.”

When it comes to retrofitting existing buildings, challenges posed by ICC 500 requirements and associated costs often make this approach impractical. As noted in AISC Design Guide 35, retrofitting existing structures requires careful consideration of various factors, from foundation modifications to structural isolation. Because of this, most projects look to new construction rather than retrofitting.

Similarly, the industry shows a clear preference for standalone shelters over those attached to existing structures. While attached shelters are allowed, it requires designing for maximum applicable loads in addition to normal storm shelter loading. This complicates the design process and often incurs increased costs. When attachments are necessary, they’re typically limited to simple elements like entrance canopies, which can be designed to account for storm conditions while maintaining the shelter’s structural integrity. “We typically would prefer to do standalone structures,” Mathew Sleiter explains. “That doesn’t mean standalone as in it can’t be part of a campus, but standalone in a structural attachment point of view.” This approach simplifies the permitting process, peer review and overall design implementation while ensuring optimal protection during severe weather events.

Professional Collaboration and Resources

For engineers new to storm shelter design, utilizing available resources is crucial. “There are a lot of resources out there. It’s important to make sure you do your due diligence and read the code to make sure you comply because there’s a lot of information and products in our industry that can be misleading and don’t always completely comply with ICC 500 requirements for storm shelters. We come across it a fair amount on a proof-rated system, whether it be doors, louvers, windows, things of that nature,” Andrew advises. “Going on to NSSA’s website and FEMA has a lot of great documentation for means and methods and general guidance on how to design shelters. It’s a great starting point for engineers and design professionals on a team that are doing a shelter for their first time.”

The design process requires extensive collaboration among various professionals and regular coordination meetings specific to storm shelter components are essential, as even small changes can have significant ripple effects throughout the project.

As severe weather events continue to impact communities across the country, the importance of well-designed storm shelters cannot be overstated. Through careful material selection and thoughtful design approaches, engineers and architects are creating increasingly resilient structures that protect communities when they’re most vulnerable.