Providing Safe and Functional Shelter from Severe Weather Events
12 Apr 2022
An overview of the standards and guidance that exist to ensure areas of refuge keep occupants safe during hurricanes and tornadoes
In the U.S, the arrival of spring means a heightened risk in many parts of the country for hurricanes and tornadoes, which cause tremendous devastation to countless people every year. People who live where severe weather events are common benefit from access to storm shelters or safe rooms in which they can stock food and supplies and take refuge if it becomes necessary. To ensure that these shelters can withstand the effects of hurricanes and tornadoes, they must meet International Code Council (ICC) requirements and, in some cases, Federal Emergency Management Agency (FEMA) guidance document requirements.
Before we explore storm shelter and safe room construction requirements, let's look at how hurricanes and tornadoes are classified and categorized.
Hurricanes are classified according to the Saffir-Simpson Hurricane Wind Scale, which ranges from Category 1 to Category 5, and is determined based on the measured maximum sustained windspeed. Damage for a Category 1 hurricane is largely constrained to shingles, siding, trees, and power outages on the order of a few days. As the Category increases in scale, levels of damage escalate until Category 5, where a significant percentage of framed homes are expected to be destroyed and the overall area may be uninhabitable for weeks or months.
While hurricanes are classified based on measured sustained wind speeds, tornadoes are classified using the Enhanced Fujita scale, which uses observed storm damage to estimate the wind speeds during the event. The scale ranges from EF0 to EF5 and an EF4 or EF5 tornado can be expected to completely destroy a well-constructed residence and leave only a clean-swept slab.
Now that you have an understanding of storm classification, let's talk about the standards and guidance that regulate the construction of storm shelters and safe rooms: ICC 500, FEMA P-361, and FEMA P-320.
ICC 500 is the governing document for the design and construction of storm shelters in the U.S., with the most recent revision in 2020 (ICC 500-2020). ICC 500 is an ANSI consensus standard that is referenced in the International Building Code (IBC), International Existing Building Code (IEBC), and International Residential Code (IRC). ICC 500 provides different definitions and requirements for residential and community storm shelters. ICC 500 storm shelter design requirements address structural aspects like rain loads, roof live loads, flood loads, wind loads, and debris hazards, as well as non-structural aspects like ventilation, shelter access, siting, latching hardware, and fire safety.
FEMA Publication 361, or P-361 is a guidance document that presents the funding criteria required for the use of FEMA grant funds for the construction of a safe room. FEMA P-361 requires full compliance with the requirements of ICC 500-2020, but also includes guidance and best practices for the design and operation of safe rooms along with additional requirements regarding safe room siting, design wind speed for residential safe rooms, and fire-resistance-rated construction. FEMA P-361 discusses both community and residential safe rooms but, unlike ICC 500, is not referenced by the IBC, IEBC, or IRC. FEMA P-320 applies the requirements of ICC 500-2020 and FEMA P-361 specifically to residential safe rooms and provides prescriptive plans for site-built safe rooms serving one- and two-family dwellings.
It is important to note that not all "shelters" are equivalent and not all areas called a "shelter" meet the requirements for life-safety protection during extreme weather events. Therefore, FEMA has developed the following specific definitions pertaining to different levels of extreme-wind refuge areas to differentiate between the area classifications as well as separate them from other "shelters".
- A Storm Shelter meets the requirements in the ICC 500 standard.
- A Safe Room meets the requirements in the ICC 500 standard and the more stringent FEMA Funding Criteria for near-absolute life-safety protection in FEMA P-361. Because all safe room criteria in FEMA P-361 meet or exceed the storm shelter requirements of ICC 500, all safe rooms are storm shelters but not all storm shelters are safe rooms.
- Best Available Refuge Areas are areas that don't meet the criteria of a storm shelter of safe room but have been determined by a registered design professional to be the area least vulnerable to the life-threatening effects of extreme wind and wind-borne debris associated with a tornado or hurricane.
As you can see, there is much to consider when designing and manufacturing storm shelters and safe rooms. For a more in-depth discussion of the ICC and FEMA requirements, applicable test methods, and certification process for shelters and their components, visit our ICC 500 Testing and Certification Solutions for Storm Shelters page or watch our ICC 500 Storm Shelters and Shelter Components: Testing and certification for building code compliance on-demand webinar.