Life Safety

Best Practices in Tornado Resistant Construction - Utilize ICB in a Continuous Load Path

Tornado-resistant con­struc­tion is essential in the United States where an average of 1253 tornadoes occur annually and can produce wind speeds of more than 200 mph. Because tornadoes are unpre­dictable and violent, their destruc­tion is often wide­spread. According to the National Oceanic and Atmos­pher­ic Admin­is­tra­tion (NOAA) tornadoes cause an average of 60 – 65 fatal­i­ties and 1,500 injuries each year. Tornado Alley is hit par­tic­u­lar­ly hard by the occur­rence of tornadoes. Tornado Alley is unof­fi­cial­ly a region from central Texas, northward to northern Iowa, and from central Kansas and Nebraska east to western Ohio. It is a region where cold, dry air from the northwest, warm dry air from the southwest, and warm, wet air from the southeast clash. The collision of these three weather systems fre­quent­ly results in intense thun­der­storms and violent tornadoes. In Texas alone, between the years of 1991 and 2010, there was an annual average of 155 tornadoes, more than any other State. In addition, Texas averages annually 2.8, EF-31 to EF‑5 tornadoes. Tornado resistant con­struc­tion is essential for the pro­tec­tion of a building and its occupants from dis­as­trous outcomes during a tornado emergency.

A Continuous Load Path Protects a Building’s Integrity When Under Attack from a Tornado

FEMA highly rec­om­mends a safe room for maximum safety to a build­ing’s occupants during a tornado emergency. However, a tornado-resilient design of the entire building is ulti­mate­ly the best pro­tec­tion of lives and the structure. A con­tin­u­ous load path is the best defense towards holding a building together when the high winds of a tornado try to pull it apart. The con­tin­u­ous load path ensures that when a load, including lateral (hor­i­zon­tal) and uplift loads, attacks a building, the load will move from the roof, wall and other com­po­nents toward the foun­da­tion and into the ground. A strong con­tin­u­ous load path is essential to holding the roof, walls, floors and foun­da­tion together during a tornado or other extreme wind event.

Insulated Concrete Blocks Build Tornado Resistant Buildings

Buildings con­struct­ed with insulated concrete blocks (ICB) maintain their integrity during the intense winds of a tornado. Insu­lat­ing concrete blocks can withstand winds of over 200 mph. Buildings con­struct­ed of concrete blocks are much stronger than wood and steel-framed buildings under severe wind events. In fact, a study published by the Portland Cement Asso­ci­a­tion (PCA), compared the struc­tur­al load resis­tance of insu­lat­ing concrete form (ICF) walls to con­ven­tion­al­ly framed walls. The study concluded that concrete walls have a much higher struc­tur­al capacity and stiffness to resist the in-plane shear forces of high wind than wood or steel framed walls. The strength of concrete walls results in less lateral twists and damage to non-struc­tur­al elements of a building such as the plumbing and elec­tri­cal. Utilizing insulated concrete blocks for tornado-resistant con­struc­tion can maintain a build­ing’s integrity during a strong tornado event. 

Insulated concrete blocks (ICB) can also resist damage from flying debris traveling over 100 mph. A study by Texas Tech Uni­ver­si­ty compared the impact resis­tance of wind driven debris between ICF walls and con­ven­tion­al­ly framed walls. The study found that ICF walls resist the impact of wind driven debris. Con­ven­tion­al framed walls, however, failed to stop the pen­e­tra­tion of airborne hazards. Insulated concrete walls are the best pro­tec­tion from windblown debris to a building and its occupants.

The Bautex Wall System Stands up to a Tornado’s Strength

The Bautex Wall System has the strength to resist the heavy winds and flying debris of the strongest tornado. The Blocks meet the Federal Emergency Man­age­ment Agency FEMA 320 and FEMA 361 guide­lines in storm zones with wind speeds up to 250 miles per hour. The Bautex Block also has the strength and mass to resist the impact to wind driven debris at speeds greater than 100 mph. In addition to severe weather resis­tance, Bautex Blocks have the thermal per­for­mance required by the IRC and IBC and are fire-rated, noise-reducing, and easy to install. Bautex Walls are a good choice when designing for tornado-resistant construction.

The National Weather Service Ratings of Tornadoes — EF-Scale

In 2007, the National Weather Service imple­ment­ed the Enhanced Fujita Scale (EF-Scale). The scale deter­mines a tornado’s strength based on the destruc­tion it caused. The scale ranges from one to five, with five being the most intense. The EF-Scale considers 28 damage indi­ca­tors such as building type, struc­tures, and trees. Each damage indicator has eight degrees of damage ranging from the beginning of visible damage to complete destruc­tion of the damage indicator.

A safe room is a space within or nearby a building, that provides near perfect pro­tec­tion during tornadoes and hur­ri­canes, according to FEMA guide­lines. A FEMA safe room is designed and con­struct­ed as specified in FEMA P‑361, and FEMA P‑320.