As extreme weather events become increasingly common, storm shelters are becoming more crucial across the US. In particular, hailstorms, tornadoes, and dramatic temperature swings have increased in the southern part of the US over the past few years. The upcoming decades are expected to have a similar perspective. Communities are looking into long-term, affordable options like precast concrete building to protect inhabitants.

A safe room is a fortified building created especially to meet FEMA requirements and offer nearly complete protection from extreme wind occurrences, such as tornadoes and hurricanes.

The occupants of a safe room constructed in accordance with FEMA guidelines will have a very high possibility of being protected from harm or death, according to our present understanding of tornadoes and hurricanes. This level of safety is referred to as "near-absolute protection."

Precast concrete satisfies every requirement for safe rooms in FEMA P-361. For storm shelters, it can be applied at the most fundamental design level. FEMA has stricter regulations than other building codes and mandates near-absolute protection for occupants during extreme weather events from wind and debris. The FEMA-selected wind speeds emphasize safety and call for the capacity to resist winds exceeding 250 mph. These exacting requirements are met by precast concrete.

Precast concrete gives value to a building in addition to protecting its residents. Precast provides structures a number of additional advantages, including:

• strengthened structural integrity

• protection from strong winds

• shorter construction periods

• advantages of thermal mass

Precast buildings sometimes function as multipurpose constructions and are built with gyms or auditoriums in mind. When individuals are compelled to utilize the shelter due to an extreme weather occurrence, these additional design features offer comfort and ease. The environment for inhabitants is improved by thick, insulated precast walls that absorb sound and FEMA-rated windows that let in natural light.

Advantages of Precast Storm Shelters

Structural Integrity

In order for a structure to be considered structurally sound, it must be stronger than the highest possible service stress or storm loading. A precast concrete safe room's structural integrity enables it to withstand service loads independently, without relying on surrounding support materials or soils. The building is deemed suitable to carry out its function if the planned strength of a precast concrete safe room exceeds the anticipated maximum applied stresses by an acceptable factor of safety and it complies with the extra FEMA 320 and FEMA 361 requirements.

Wind Protection

Tornadoes, hurricanes, and other such catastrophes rarely produce constant high winds. The pressure and stresses on the various components of a structure increase due to the constant varying and changing of wind speeds and directions. Wind forces operating on both sides (inside and outside) of a safe room structure will also have an impact.

Access and Entry

When choosing a secure room, access points are a crucial aspect to take into account. Easy accessibility, resistance to missile-type forces, and adequate attachment to a structural backing material are all characteristics that can be easily addressed in a precast concrete design for an access point (a door or window). Doors that comply with ICC-500, Section 306.3.1; windows that comply with ICC-500, Section 306.3.2; and all other openings that comply with ICC-500, Section 306.4 are valid entry and exit points for authorized precast concrete safe rooms that can survive tornado events.

Transportation and Installtion

Safe rooms made of precast concrete can be produced well in advance of installation on site. There is no need to wait for cast-in-place concrete buildings to set or cure because they are fully cured before being delivered to the site. Precast concrete safe rooms are readily available, competitively priced, and ready for use as soon as they are delivered. When compared to other materials, these precast advantages can save a project valuable days, weeks, or even months.

Thermal Mass

In the construction business, the term "thermal mass" refers to a material's natural capacity to absorb heat energy. The daily temperature changes in the building's internal spaces can be reduced by using a wall material with a high thermal mass. Because precast concrete has a high thermal mass, it requires a significant amount of heat energy to adjust its temperature. Because safe rooms are intended to house numerous people for an extended period of time, and because the ventilation and temperature within are crucial to ensuring occupant health and safety, the capacity of precast to moderate temperature changes is significant.

Ventilation

The 2006 IBC and IRC codes1 are applicable if the local jurisdiction has not issued a building code; ventilation in approved precast concrete safe rooms complies with the building codes or regulations adopted by the local jurisdiction. Precast concrete safe rooms have ventilation through either the ceiling or the floor. Any ventilation apertures must be shielded with a shield or cowl that passes missile impact testing. When specifying a precast concrete safe room, it is conveniently satisfied the requirement for mechanical ventilation if the safe room is intended for occupancy of more than 50 persons. During the precast manufacturing process, ventilation apertures are simply created and placed to precise requirements.

FAQs about Precast and FEMA Storm Shelters

What is the best material for a storm shelter?

One of the most typical materials found in shelters is concrete. It is quite heavy and loses some of its mobility in strong winds. There aren't many anchorages, extra fixtures, or installation needed. It is more affordable than other materials like steel, works well for many different storm shelter designs, and has a track record of withstanding severe weather.

How thick should a concrete storm shelter be?

According to FEMA, foundations must be at least 3.5 inches thick and in many cases winds will create loads that need greater thicknesses. More information and technical details from FEMA can be found here.

What types of materials are storm shelters made from?

Storm shelters can be made from a variety of materials including wood, steel, and concrete.  Some shelters make use of more than one of these materials that work together to provide protection to the occupants inside.

Robert J Curry Public Safety Center

The Robert J Curry Public Safety Center is built to FEMA 361 design and construction guidance for community shelters and can withstand the stringent 200 mph wind requirements. It is also used as a first responder shelter to house more than 275 personnel for pre and post-disaster functions.  The project consisted of 563 pieces of over 68,000 SF of exterior cladding most of which are 8” thick architectural precast concrete walls.

Precast Resiliency Resources

PCI recently highlighted precast and its ability to perform well in storms in their Ascent magazine.  Read some of the articles below.