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
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.
