Storm shelters and safe rooms are essential for safeguarding residents in regions vulnerable to severe weather events like tornadoes and hurricanes. The design and construction of shelters for use during significant high-wind weather events must follow standards and guidelines set by the United States government and third-party associations. This includes products used in the construction of the shelter, including louvers.
The two main entities involved are the Federal Emergency Management Administration (FEMA) and the International Code Council (ICC).
Photos courtesy Airolite
FEMA provides guidelines for both community and residential safe rooms. FEMA Publication P-361, Safe Rooms for Tornadoes and Hurricanes: Guidance for Community and Residential Safe Rooms, provides important information about safe room design and construction, including best practices. These best practices include consideration for ventilation requirements, emergency management, and risk assessment information.
ICC 500, Standard for the Design and Construction of Storm Shelters, is another essential resource, as this document systematically arranges FEMA P-361 and provides the building codes and standards for storm shelter design and construction. Any safe rooms constructed using FEMA funds must comply with ICC 500 and FEMA P-361 requirements.
Figure 1, the wind zone risk level map, helps identify when a tornado safe room or storm shelter using FEMA 361 louvers is recommended.
Design considerations
An important aspect of storm shelter design is protecting openings, including the ventilation openings, against extreme wind and wind-borne debris while still providing adequate airflow to the shelter occupants. Wind speeds up to 402 km/h (250 mph) must be considered when designing these storm shelters for tornado regions. Proper product selection and application are critical to maintaining building envelope ratings.
One of the main design criteria relative to the building envelope is missile impact resistance. Missile impact criteria for impact-protective systems, including
louvers, are identified in ICC 500, Chapter 8. The missile used in testing is a No. 2 or better grade soft lumber 2×4 weighing 6.8 kg (15 lb) with a length of 4 m (13.5 ft). For a safe room designed to withstand a 402-km/h (250-mph) wind speed, the missile speed will be 161 km/h (100 mph) for vertical surfaces and 108 km/h (67 mph) for horizontal surfaces.
Chapter 8 of the ICC 500 publication also includes pressure-testing procedures for impact protective systems, including positive and negative cyclic design pressures. This procedure subjects the test specimen to very high positive and negative wind loads. It is designed to ensure the impact-protective system can withstand the wind-induced pressure experienced during a significant weather event.
The ICC 500 publication also clearly identifies ventilation requirements, which vary based on the storm shelter application and occupancy. Residential shelters (maximum occupancy is 16 people) require 1,290 mm2 (2 in.2) of venting area per occupant. Community shelters with occupancy of 50 or fewer require 3,226 mm2 (5 in.2) of venting area per occupant, and occupancy of 50 or greater requires 3,871 mm2 (6 in.2) of ventilation per occupant. This section also provides specific information for the proper location and placement of natural ventilation openings within the structure. The location of the ventilation openings is critical to providing adequate cross ventilation for the shelter.
Section 112 of the ICC 500 publication addresses labeling. This section explains the requirements for labeling of impact protective systems, including louvers, to show compliance with the ICC 500 standard. An approved agency, such as Underwriters Laboratories (UL), labels these products when required by the applicable code or jurisdiction.
FEMA louver requirements
Louvers meeting FEMA requirements are a common selection when it comes to protecting ventilation openings in the structure’s envelope. When using louvers in FEMA shelter applications, verifying that the selected louvers have the ICC 500 impact qualification, meet the cyclic wind load and high wind load ratings, and have a third-party verification listing is important. UL is one example of a third-party verifier. The manufacturer may also choose to test the louver to the Air Movement and Control Association International, Inc. (AMCA) Standard 500-L for Air and Water Performance. This testing is conducted to validate a manufacturer’s published performance of the louver regarding air and water penetration performance and to allow it to be applied with confidence that it will perform as specified.
Protecting ventilation openings is essential to maintaining structural integrity and occupant safety in the design of storm shelters and tornado safe rooms. With a wide variety of installation and configuration options available, louvers meeting FEMA requirements can be configured for nearly every safe room and storm shelter application. This installation flexibility, combined with the stringent testing qualifications and third-party listing, makes these louvers ideal for tornado safe rooms, storm shelters, and applications in the hurricane-prone region or any location where maximum protection against wind-driven rain is necessary.
Anthony Jackson, CSI, CDT, LEED Green Associate, is Airolite’s product manager. For more than 100 years, Airolite has been helping construction professionals around the world design, select, and specify architectural louvers, grilles, equipment screens, sun controls, and canopies. For more information, visit www.airolite.com.