Secret to protecting buildings from natural disasters

by arslan_ahmed | April 6, 2023 11:57 am

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Natural disasters, such as hurricanes and tornadoes, are inevitable throughout North America, leaving millions of homes exposed to damaging winds and weather conditions. Lasting a few hours to days, damage from these disasters takes years to fully repair infrastructure, rebuild homes, restore buildings, and get families and communities back on their feet.

For example, a December 2021 storm that barreled through Kentucky and neighboring states spawned at least 66 tornadoes, resulting in 89 deaths and more than 11,700 damaged buildings. In less than two days, the twisters caused approximately $2.9 billion in reconstruction costs.

This catastrophic storm, and others like it, may be unavoidable, but there are building design and construction methods to minimize property damage and save lives when a storm does strike.

One of these construction methods is insulated concrete forms (ICF). An ICF is a type of concrete formwork designed to remain in place as part of the permanent construction of a building. Primarily used for exterior walls, ICF assemblies comprise two layers of rigid insulation connected by webs to establish the core width and provide a hollow center. Once the ICFs are stacked, reinforcing bars are placed inside and concrete is pumped and consolidated to create a monolithic concrete core.

Resilient design to strengthen infrastructure

What if an impending hurricane or tornado did not have to mean total destruction? Constructing new buildings or reinforcing existing structures in accordance with principles of resilient design can reduce risks and ensure properties and occupants are protected in the face of extreme weather.

Resilient design is the proactive process of designing and constructing buildings, landscapes, and entire neighborhoods to mitigate the impact of environmental and external hazards, while maintaining livable conditions. According to the Resilient Design Institute (RDI), these design practices help “respond to natural and manmade disasters… including sea level rise, increased frequency of heat waves, and regional drought.”¹

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This systemic approach also addresses basic human needs, including reliable access to clean water, safe air, lighting, heating and cooling, healthcare, and food. Resilient design principles prioritize adaptability, sustainability, and social equity for solutions that function for both the short- and long-term.

In the construction industry, resilient design factors in material selection, assembly testing for air and water leakage, building information modeling (BIM), and integrative systems. All this requires coordination of the owner, architect, and contractor to reap the full benefits. The key advantages of applying resiliency concepts are:

• Extended service life of the building and reduced maintenance costs by effectively resisting hurricane- and tornado-force wind and airborne debris.
• Increased occupant safety.
• Continuous business operations.
• Decreased recovery time for individuals, families, and communities.

Designing and constructing to these higher standards and beyond building codes does come with increased financial investment. However, a benefit-cost analysis produced by the National Institute of Building Sciences (NIBS)—based on a 100-year project life—estimates mitigation measures save up to $13 per dollar invested.²

Storm shelters and safe rooms to protect residents and occupants

A storm shelter or safe room is a hardened structure designed to provide near-absolute protection during extreme weather events, so at least a designated portion of the building will not collapse or be damaged from wind-borne debris. In areas prone to hurricanes and tornadoes, storm shelters can be a fast, effective way to shield vulnerable communities until larger infrastructure can be retrofitted or replaced with more resilient features.

In 2008, the International Code Council (ICC) and National Storm Shelter Association (NSSA) first developed the ICC/NSSA Standard for the Design and Construction of Storm Shelters, also known as ICC 500.³ This outlines proper design, construction, and inspection of residential and community storm shelters, including considerations such as building materials, structural testing, occupant density, ventilation, and signage.

A residential safe room can be built within a home or as a stand-alone structure adjacent to a residence to accommodate no more than 16 individuals. A community storm shelter, on the other hand, is a reinforced building or portion of a building intended to hold anywhere from 16 to several hundred people.

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The Federal Emergency Management Agency (FEMA) has its own guidelines for residential and community storm shelters, which they refer to as “safe rooms” in FEMA 320 and FEMA 361.⁴

Both ICC 500 and FEMA offer criteria for a structure’s ability to withstand wind loads, rain loads, hydrostatic loads, pressure differentials, and wind-borne debris loads.

Regions of the U.S. that fall within the 402 km/h (250 mph) wind-speed zone for tornadoes are required to have ICC 500-compliant storm shelters with the following building types:⁵

• K-12 schools
• Daycare facilities
• Emergency operation centers
• Fire, rescue, and ambulance stations
• Police stations
• 911 call centers
• Military installations

It is important to note how the design criteria for tornado and hurricane shelters differs due to the varying wind pressure, speed, and duration of the storms. Other factors impact the execution of these codes based on the structure’s occupant density, water supply, ventilation, and access to emergency power.

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How do ICFs fit into resilient design?

While resilient design is broad and can be executed in numerous ways, new construction projects can easily apply these principles with the use of ICFs.

Once cured, the monolithic concrete wall is almost impenetrable, and the rigid insulation offers superior thermal protection of R-24, continuous and soundproofing of sound transmission class (STC) 50 plus, with concrete cores of 152.4 mm (6 in.) and greater. While an ICF core can be as narrow as 101 mm (4 in.), forms used specifically for disaster resilience are usually 203 to 304 mm (8 to 12 in.) wide. Further, an ICF wall thickness of 152.4 mm (6 in.) and greater core provide four-hour fire Underwriters Laboratories (UL) Listing–U930.

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ICFs provide monolithic concrete which satisfies the air barrier code requirement minimum.  However, seeking to build to a higher standard, many architects are adding a vapor permeable fluid applied membrane to fully seal the envelope. Impermeable membranes are also sometimes used on coastal installations.

Ultimately, code requires the ICF foam surface to be covered and not exposed to the elements requiring the addition of brick, stone, or stucco facade.

The polypropylene webs that hold the panels together and rebar in place within the core also extend within the foam to almost the face of the wall on both sides (15.8 mm [0.625 in.] away). They have approximately one-and-a-half times the axial pullout of a 2×4 and are used to directly attach sheet rock and minor cabinetry. For heavy items, such as cabinetry or steel embed connections, the concrete can be allowed to flow to the face of the form.

For storm shelters, rough openings for windows and doors are typically framed with lumber, which is removed after the pour to provide direct anchorage to the concrete. Steel integrated framing assemblies are also available on the market which encase the rough opening in thermally broken steel for attachment of windows and doors. Electrical and plumbing is also cut into or routed in the foam post-concrete pour. Sheetrock is attached directly to the foam via the 38 mm (1.5 in.) wide furring strips that run floor to ceiling every 203 mm (8 in.).

Brick ties are available to attach to the external webs; however, for most storm shelters, brick ties are usually embedded in concrete prior to pouring.

The endurance and energy-saving benefits of ICFs can apply to any type of structure, from storm shelters and single-family homes to apartment buildings and schools.⁶ ICFs are especially useful for building critical infrastructure, such as hospitals and fire stations, to ensure consistent services during an emergency.

ICFs offer continuous exterior insulation, which virtually eliminates thermal bridging so, in a power outage, ICF buildings maintain interior temperatures for much longer than those using insulation installed within the stud cavities of wood- or steel-framed construction. Thus, they are less reliant on HVAC systems to keep occupants safe and comfortable.

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To assess the durability of ICF construction, ABC Domes and Wind Science & Engineering Research Center Debris Impact Test Facility at Texas Tech University conducted debris impact testing, in accordance with ICC 500 and FEMA criteria. A 6.8 kg (15 lb) 2×4 was shot at an ICF wall at 161 km/h (100 mph) to simulate airborne debris hitting a structure at 402 km/h (250 mph), equivalent to an F4 tornado. The results indicated that while the wood penetrated the foam, the concrete core stopped the projectile, keeping the structural elements of the wall intact.⁷

In real-world hurricanes and tornadoes, ICFs have proven themselves stronger than wood-frame construction. In 2018, when Hurricane Michael struck Mexico Beach, Florida, hundreds of oceanfront properties were demolished or severely damaged; except for one. An ICF home, known as the Mexico Beach “Sand Palace,” stood alone and unscathed among the wreckage.⁸ 

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Building beyond natural disasters: An ICF case study

In Honolulu, Hawaii, ICFs were used to construct two new five-story buildings as part of the Schofield Army Barracks, each housing 100 soldiers. As per the United States Department of Defense (USDOD), the structures were designed to anti-terrorism/force protection (AT/FP) standards, which are codes to prevent building collapse and damage from explosives, minimize human injury and death, reduce mission degradation, and preserve government property.⁹

More specifically, UFC 4-010-01, Minimum Antiterrorism Standards for Buildings, provide applicability of the “government unique criteria for typical design disciplines and building systems, as well as for accessibility, antiterrorism, security, high performance and sustainability requirements, and safety.”¹⁰

ICFs fulfilled these standards, met seismic design criteria, and even helped the buildings achieve Leadership in Energy and Environmental Design (LEED) gold status.

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While these conditions are certainly different from hurricanes and tornadoes, they reinforce the case for using ICFs in applications where durability is most needed and life safety is at greatest risk.

Resilient design and ICFs

To combat devastation caused by hurricanes and tornadoes, many homeowners, city officials, and building professionals are turning to resilient design. These preventative practices reinforce the longevity of existing and new buildings, which, in turn, increases personal safety and economic stability during natural disasters.

ICF construction meets resilient design standards, as well as ICC 500 and FEMA criteria for storm shelters and safe rooms. ICFs are frequently used in residential and commercial buildings as well, for their strength, energy-efficiency, and sound-dampening qualities that exceed the performance of conventional wood-framing.¹¹

By proactively building with ICFs and incorporating other resilient design techniques, families, businesses, and entire communities can be at peace knowing they are protected during the most severe weather events.

Notes

¹ Learn more about resilient design, visit www.resilientdesign.org/what-is-resilience[9].

² Read the report on the benefit-cost analysis,
www.nibs.org/projects/natural-hazard-mitigation-saves-2019-report[10].

³ See ICC/NSSA Standard for the Design and Construction of Storm Shelters, codes.iccsafe.org/content/ICC5002020P1[11].

⁴ See the FEMA guidelines for residential and community storm shelters, www.fema.gov/sites/default/files/documents/fema_safe-rooms-for-tornadoes-and-hurricanes_p-361.pdf.[12]

⁵ See FEMA ICC-500 2020 highlights, www.fema.gov/sites/default/files/documents/fema_ICC-500-2020-highlights_publication_082021.pdf[13].

⁶ Read more ICF safe rooms, www.nudura.com/company/blog/homeowners/weather-the-storm-with-an-icf-safe-room[14].

⁷ Examine the results from the impact debris testing, www.nudura.com/why-nudura/architect-engineers/icf-impact-testing[15].

⁸ Check out the ICF home, “Sand House,” www.nudura.com/company/blog/homeowners/nudura-icf-home-survives-hurricane-michael[16].

⁹ Learn about anti-terrorism/force protection (AT/FP) standards, home.army.mil/detrick/index.php/my-fort/all-services/prto[17].

¹⁰ Read the minimum antiterrorism standards for buildings, www.wbdg.org/FFC/DOD/UFC/ARCHIVES/ufc_4_010_01_2018_c1.pdf[18].

¹¹ Know more about the qualities of ICF, www.nudura.com/resources/nudura-icf-vs-wood[19].

Author

Cameron Ware is the western division key accounts executive for Tremco CPG Inc., providing Nudura installation training to architects, engineers, and insulated concrete forms (ICF) installation crews across the area. Ware has been involved with the construction of several million square feet of ICF, including more than 100 ICF schools and approximately 100 ICF-500 storm shelters.

Source URL: https://www.constructionspecifier.com/secret-to-protecting-buildings-from-severe-weather-events/

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