Ever receive a question about Insulated Concrete Forms and just did not know how to answer it? Lionel Lemay, PE, Executive Vice President, Structures and Sustainability at NRMCA has provided answers to these common questions so you are better equipped for conversations with your customers and specifiers.
1. What are the key benefits of ICFs?
a. Ideal for Low/Mid-rise
b. Competitive on First Cost
c. Fast – reduced construction cost
d. Safer Job Site – Reduces Risk
e. Easy to Use – Fewer Trades
f. Energy Efficient – Increase operating income
g. Quiet – Keep Tenants Happy
h. Fire Resistant – Reduce Insurance Costs
i. Well Established – 1000’s of case studies (www.concretetracker.org)
j. Flexible – Easily receives any finish and all building systems
2. How tall can ICF buildings go?
ICFs have been used in single story residential and commercial applications to high-rise
applications. To date, the tallest ICF building is 23 stories tall built in Waterloo, Ontario. There is a 16-story building being built in New York. ICFs are ideal for any bearing wall type building where you have relatively high percentage of solid wall with punched openings. However, they have also been used for curtain wall buildings with spandrel panels in from of the ICF walls.
3. How tall can the ICF walls go unsupported?
ICFs have been used for walls exceeding 40 feet unsupported height. The difficulty is not so much the structural design of such walls, but construction. Building a 40-foot-tall and then bracing the walls and providing a working platform for placing concrete takes skill and expertise. ICF walls come in thicknesses of 4” through 12” so engineers should select the appropriate thickness to resist loading.
4. What thickness can I use?
ICF walls come in 4”, 6”, 8”, 10” and 12” thickness (some manufacturers go even thicker). Generally, 4” walls are only used for non-loadbearing applications such as demising walls in apartments, hotels or dormitories.
5. How should I reinforce the walls?
Reinforcement is typically applied in one layer (in the center) for most above grade applications. However, for thicker walls (10-12”), reinforcement can be applied in two layers. For below grade applications with soil pressure from the outside, one could place reinforcement in one layer near the inside face.
6. How about seismic forces?
Solid concrete walls are ideal for resisting seismic forces and ICF buildings have been used for many low and mid-rise applications in high seismic regions. There would be no reason not to use ICFs for high-rise applications either. However, many taller buildings on the west coast use concrete frame or hybrid shear wall frame construction.
7. How about storm shelters?
ICFs are the ideal for building storm shelters against hurricane and tornado forces. Although the winds are high (200 mph or higher) concrete walls can easily resist wind forces. However, the key to designing a storm shelter is the ability to resist the forces from flying debris. ICFs have been tested using the “tornado cannon” where 2x4s are shot at the wall at 100 mph and as expected they do not penetrate the wall.
8. Cost of ICF walls?
ICF walls are typically lower cost than other commercial construction methods such as CMU and Steel Studs. Therefore, for commercial applications such as offices, schools, industrial and institutional buildings they are quickly becoming the system of choice because of the speed and simplicity of construction compared to other systems.
Wood frame is still less costly than ICF construction, so for single-family and multi-family construction, wood frame is often cheaper. For single-family, the added cost for using ICFs is usually 5-7%. For multi-family, the added cost is typically 1-3%. However, many owners are selecting ICFs regardless of the small added cost because all the other benefits.
9. Fire resistance of ICF walls?
Most ICF wall manufacturers have conducted the fire resistive rating test ASTM E119 and 4-inch walls typically meet 2-hour rating and 6-inch walls and thicker meet 4-hour rating. Walls must have 15-minute thermal barrier provided by 1⁄2” gypsum barrier. The foam in ICFs is fire treated and meets the flame spread requirement of 25 or less and smoke developed rating of 450 or less when tested in accordance with ASTM E84.
In certain cases, the NFPA 285 test for lateral flame propagation of exterior walls may be required. This is an assembly test that must include all finishes.
10. Finishes on ICF walls?
Nearly any finish can be attached to an ICF wall since there are furring strips at the end of each form tie that can accept a screw for fastening finishes. Drywall, brick, stucco, siding, steel panels, etc.
11. Structural connections to ICF walls?
Connecting floors or other structural components are connected to ICF walls in many ways. Concrete floors are often placed on top of a wall for bearing type connection with rebar dowels embedded in the wall and slab. For shear connections such as wood joist, typically a rim joist is attached to the side of the wall using anchor bolts through the foam into the concrete. For steel connections, an embedded plate is usually installed into the form with shear studs.
12. Concrete strengths for ICF walls?
Generally, 4,000 psi concrete is sufficient for most applications. But that does not preclude engineers from specifying higher strength concrete when required.
13. Mix specifications for ICF walls?
Strength as specified by the design engineer (measured at 28 days). Recommended maximum aggregate size 1⁄2-inch aggregate for 4 & 6-inch forms and, 3⁄4-inch for 8-inch forms and higher. Recommended concrete slump is 4 to 6-inches +/- 1-inch (102 to 152mm +/- 25mm). Where required by engineer of record, recommended slump specification shall be attained through addition of super plasticizer/mid-range water reducing agents to achieve design mix strength and concrete flow-ability.
14. Placing concrete in ICF walls?
Place concrete by pumping in 4-foot lifts maximum. Use pencil vibrators to ensure consolidation in form and around reinforcing steel.
15. Termite Resistance
Expanded polystyrene does not support, attract or provide a food source for insects (including termites). However, all buildings built in termite prone areas should follow building code and standard practice for termite protection and abatement.
16. Structural Inspection (check for voids)?
Generally, if concrete is installed by a qualified contractor, trained by the ICF manufacturer, following good concrete placement, there will not be any voids in the forms. However, if voids are suspected, there are several methods for detecting them. Pounding on the forms with your hand will reveal voids. Using a sharp, stiff probe to measure foam depth where voids are suspected is another method. If significant voids are suspected, using ground penetrating radar is an option (expensive). The last resort is to remove foam and repair voids.
17. Energy Performance?
ICFs have considerably more insulation value than conventional wall construction such as CMU, steel studs and wood studs. Around R25 depending on exterior finish. In addition, the thermal mass in the walls helps regulate temperatures. And because they are solid walls, they tend to result in more air-tight structures. All this results in buildings with considerably better energy performance with reported energy savings ranging from 20% in warmer climates to 50% or more in colder climates.
18. Sound Resistance?
Concrete walls provide superior sound reduction qualities compared to other forms of
construction. STC class starts at 50 for 4-inch walls and can go as high as STC 70 with thicker walls and additional gypsum wallboard.
Recent projects have begun using panelization methods to improve efficiency and speed of construction. Large panels are constructed off-site in a controlled factory setting, rebar placed inside, trucked to the site and craned into place. Panels are secured to each other and braced before concrete is placed.
20. Fiber Reinforcement (Helix or other)?
Some engineers are beginning to specify steel fibers in place of horizontal steel. This eliminates the need for relatively slow placement of horizontal bars and panelized construction.
21. Contractor training (Formal industry training and certification?)
Most ICF manufacturers have a formal training program for their system. Make sure you specify that contractors must have successfully passed the training program. CRMCA will be hosting and ICF and NRMCA approved training course in February 2019.
CRMCA is a resource for you, our valued members, as well as your customers and specifiers. For more information on Design Assistance and upcoming Education Offerings, contact Jessica Palmer, Director of Business Development and Education. Jessica@crmca.com