Insulated concrete forms: The future of resilient building design

by arslan_ahmed | April 24, 2023 8:00 pm

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By Cameron Ware

Natural disasters are inevitable throughout North America, leaving millions of households 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 barrelled through Kentucky and neighbouring 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, are unavoidable, but there are building design and construction methods to minimize property damage and reduce the loss of lives when a storm does strike.

One of these construction methods is insulating (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 expanded polystyrene (EPS) insulation connected by webs to establish the core width and provide a hollow center. As the ICFs are being stacked, reinforcing bars are placed inside and once the concrete is pumped and consolidated to create a monolithic concrete core.

Offers stronger built construction

What if an impending hurricane or tornado did not have to mean total destruction? Designing or reinforcing structures with durability are the answers to reducing risks and ensuring properties and occupants are better protected in the face of some types of extreme weather.

Resilient design is the proactive process of designing buildings, landscapes, infrastructure, and entire neighbourhoods to mitigate the impact of environmental 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

Resilient design principles prioritize adaptability, sustainability, and social equity for solutions that function for both the short- and long-term. At their core, ICFs are monolithically poured concrete walls and significantly stronger than all types of conventional construction. This statement is substantiated by the fact that they are accepted by the ICC-500 for the construction of 402-km/h (250-mph) rated storm shelters.³

In the construction industry, resilient design considers material selection, assembly testing for air and water leakage, building information modelling (BIM), and integrative systems. All this requires co-ordination of the owner, architect/engineer, 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.

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Designing and constructing to these higher standards and beyond building codes does come with increased financial investment.

Storm shelters and safe rooms to protect residents

A storm shelter or safe room is a hardened structure designed to provide near-absolute protection during extreme weather events. ICFs are not impacted by drought or extreme heat or cold. The ICF structure in flooded buildings can often be dried out and restored because they do not contain biodegradable materials subject to mould. This is not the case for wood structures, some may need rebuilding from the ground up to reach areas of the structure which are not underwater.

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 U.S., via 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. 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 intended to hold anywhere from 16 to several hundred people.

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 centres
• Fire, rescue, and ambulance stations
• Police stations
• 911 call centres
• 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 a structure’s occupant density, water supply, ventilation, and access to emergency power.

The National Building Code of Canada (NBC 2020) offers similar design criteria through importance categories, which can be determined by the NBC forming Part of Sentence 4.1.2.1.(3) Table 4.1.2.1.B.:

• Low Importance—low direct or indirect hazard to human life
• Normal Importance—all buildings not otherwise defined
• High Importance—buildings likely to be used as post-disaster shelters with a primary use as a school or community centre
• Post-disaster buildings

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The post-disaster building category best reflects the ICC500 and FEMA guidelines for storm shelters in the U.S. For the definition of a post-disaster building category, the NBC Part 1 A-1.4.1.2 identifies essential structures and their services (Figure 1). All buildings under the definition of a post-disaster building must retain a professional engineer to undertake responsibility of the design to Part 4 of the NBC.

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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 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 a four-hour fire UL Listing–U930.

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 vapour 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 be covered and not left exposed to the elements requiring the addition of brick, stone, or stucco facade.

The polypropylene webs holding 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 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 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, some storm shelter engineers require brick ties to be embedded in concrete prior to pouring the concrete.

The durability and energy-saving benefits of ICFs can apply to many types of structure, from storm shelters and single-family homes to apartment buildings and schools. ICFs are especially useful for building critical infrastructure, such as hospitals and fire stations.

Since ICFs offer continuous exterior insulation, which virtually eliminates thermal bridging, ICF buildings maintain interior temperatures for much longer than those using wood or steel frames. And since the conduction of the framing itself is such, the addition of foam insulation to the cavity has virtually no thermal benefit. In a power outage, ICF structures are less reliant on HVAC systems to keep occupants safe and comfortable.

The Insulating Concrete Forms Manufacturers Association (ICFMA) thermal study, conducted by CLEB Laboratory Inc., reports the key data is the tested ICF wall assembly provided 58 per cent better effective R-value/RSI than the tested 50.8 x 152.4 mm (2 x 6 in.) insulated wood frame cavity wall assembly. In addition, the ICF wall assembly generated up to 60 per cent energy savings compared to the tested 50.8 x 152.4 mm (2 x 6 in.) wall assembly. Note that the tested wood frame wall assembly meets the NBC for above-grade residential walls and the 2015 International Residential Code (IRC) in the U.S. for climate zones one to five.⁶

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To assess the durability of ICF construction, ABC Domes and the 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.

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.

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Built beyond natural disasters: An ICF case study

In Honolulu, Hawaii, ICFs were used to construct two new five-storey 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.⁷

More specifically, UFC 4-010-01, Minimum Antiterrorism Standards for Buildings, provide applicability of “government unique criteria for typical design disciplines and building systems, as well as for accessibility, antiterrorism, security, high performance and sustainability requirements, and safety.”⁸

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

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.

Conclusion

To combat devastation caused by natural disasters and extreme seismic events, many homeowners, city officials, and building professionals are turning to resilient design.

Building codes are evolving alongside these preventative practices to 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, FEMA, and the NBC criteria for storm shelters, safe rooms, and post-disaster buildings. ICFs are frequently used in residential and commercial buildings for their strength, energy-efficiency, and sound-dampening qualities that outmatch conventional wood-framing.

Notes

¹ Learn more about resilient design, visit www.resilientdesign.org/the-resilient-design-principles/[7].

² Read the report on benefit-cost analysis, www.nibs.org/projects/natural-hazard-mitigation-saves-2019-report[8].

³ See ICC/NSSA Standard for the Design and Construction of Storm Shelters, codes.iccsafe.org/content/ICC5002020P1[9].

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[10].

⁵ See FEMA ICC-500 2020 Highlights www.fema.gov/sites/default/files/documents/fema_ICC-500-2020-highlights_publication_082021.pdf[11].

6 Read the thermal study, www.icf-ma.org/resources/thermal-study/[12].

⁷ Learn about anti-terrorism/force protection (AT/FP) standards, home.army.mil/detrick/index.php/my-fort/all-services/prto[13].

⁸ Read the minimum antiterrorism standards for buildings, www.wbdg.org/FFC/DOD/UFC/ARCHIVES/ufc_4_010_01_2018_c1.pdf[14].

[15]Author

Cameron Ware is 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.constructioncanada.net/insulated-concrete-forms-the-future-of-resilient-building-design/

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