Insulating concrete form or insulated concrete form (ICF) is a system of formwork for reinforced concrete usually made with a rigid thermal insulation that stays in place as a permanent interior and exterior substrate for walls, floors, and roofs. The forms are interlocking modular units that are dry-stacked (without mortar) and filled with concrete. The units lock together somewhat like Lego bricks and create a form for the structural walls or floors of a building. ICF construction has become commonplace for both low rise commercial and high performance residential construction as more stringent energy efficiency and natural disaster resistant building codes are adopted.
ICFs have a long history, and in fact were an offshoot of the original products, which is what we now consider the “alternative” ICFs. In Europe around the time of World War II, blocks were made of treated wood fibers held together by cement. During the post-war years when plastic foams were developed, both a Canadian and Europeans developed similar blocks. Today, ICFs are an accepted system within all building codes in North America.
Various ICF Formats
Within ICFs there are a variety of formats. The block system is the smallest of all. Flat” or “panel” systems are similar to a conventionally poured wall. The result is a wall of uniform flat thickness similar to a conventional cast-in-place wall. The foam panels are connected with plastic or steel ties that hold them in place.
Quad-Lock Insulated Concrete Forms and LiteForm are flat panel systems using panels and ties. LiteForm is a folding block system in which the polypropylene ties are on their patented “living hinge” which allows the forms to fold flat for shipping.
BuildBlock’s GlobalBlock is an example of the screen grid system. Grids can either be in the screen grid shape, which resembles the shape of window screen, or a waffle grid, which has the screen grid shape but thicker and thinner. BuildBlock is an all-foam ICF, intended to provide a lower-cost ICF for structures finished using stucco and plaster. This system uses more foam, reducing concrete and increasing R-value, but is not a monolithic ICF.
“Plank” systems are narrower horizontal planks that stack vertically. Planks are longer like panels in the horizontal direction but shorter like blocks in the vertical dimension. “Post and beam” systems have horizontal and vertical columns of concrete that are completely encapsulated in foam insulation. The two sandwich pieces that provide insulation are connected in various ways of materials made from plastic, metal, or other connectors. The spacing between the structures can be customized. Vertical ICFs are assembled primarily from the ground and poured vertically and are similar to traditional removable concrete forms. Vertical ICFs use more foam, but less concrete.
The Hobbs Contour Wall is a modified post and beam system that places concrete only where it is structurally necessary, to use less. The system is described a essentially being a series of columns at 16 inches on center spacing, just like a wood stud wall, except that it’s a monolithic concrete wall. The system is said to require much less bracing than others, which reduces overall expense and requires no special ICF bracing.
Alternative ICFs
Alternatives to so-called conventional ICFs include Composite ICFs, Wood Fiber Blocks, and SCIP (Structural Concrete Insulated) Panels.
Composite ICFs
Composite ICFs are panels made from a mix of recycled expanded polystyrene (EPS) and Portland cement. The Perfect Block made by Eco Building Systems is an example of this type. These blocks are heavier and require less bracing, which means construction can proceed quickly and with less labor. The Perfect Blocks are heavier than others, and require less bracing, which means construction can proceed quickly.
Composite ICFs are considered a green option, because of the recycled EPS that is usually destined for the landfill. The original composite ICF block was invented by Rastra in 1972 and used 100% post-industrial, post-consumer waste. Jerry Kachlic, founder of Eco Building Systems, uses 100% repurposed EPS expanded polystyrene saved from items that would normally go to the landfill. Perfect Block has a smaller core, yet is engineered to the same criteria of a 4-hour fire rating and withstanding 250 mile per hour winds. Their tested block design takes 35% less concrete fill than other 6-inch core block, saving costs.
Wood Fiber Blocks
Manufacturers of wood fiber blocks define themselves as the original ICF insulated concrete form work. Manufacturers include Durisol in the UK, ShelterWorks and Faswall in the United States, and Nexcem which is made in Canada. When the products were first being made in Europe in the late 1930s, the goal was to create a product using waste material. In these blocks, the wood fibers are treated to neutralize the sugars and proteins. The process is called mineralization, and once that’s done the material can be formed into blocks. Although these blocks originated in Europe, bricks and stone are the primary construction materials there and ICFs are rarely used. These blocks are also sometimes called mineral fiber blocks.
Faswall, made in Oregon by ShelterWorks, weighs 28 to 30 pounds per block. Another difference is dimensional — Faswall is 8 inches tall where Durisol is 12. Faswall is said to use 0.33 cubic feet of concrete per square foot compared to .5 cubic feet per square foot in a 6-inch traditional ICF wall. The only ingredients in Faswall and other similar systems are mineralized wood chips (85% for Faswall) from recycled wood and portland cement/slag cement binder (15% for Faswall). Because the material stores or releases water vapor depending on the environmental conditions, the block keeps the indoor relative humidity at a healthful and comfortable level. Faswall’s vapor permeability is claimed to also keep relative humidity levels low enough that mold doesn’t grow, and the high (alkaline) pH of the composite material also inhibits mold growth. As with most ICFs, Faswall’s fire rating is said to be 4 hours with zero flame spread as opposed to 15 minutes for a comparable wood framed wall. Both stucco and drywall can be applied directly to the Faswall block, and the surface remains durable and puncture proof.
Structural Concrete Insulated Panels (SCIP Panels)
Structural concrete insulated panel (SCIP) wall construction is different from ICF in that the concrete is applied to the outside of the foam whereas on the ICF application, concrete is pumped inside the foam, although they both have a high insulation value and strength. The technology has been around since the early 1970s. It involves 2.5 and 4-inch thick rigid EPS foam panels placed between two sheets of 11 gauge galvanized mesh that are held an inch from the foam by diagonal truss wires which run through foam and are welded to the mesh. The panels are 4 feet wide and can be cut to whatever length the contractor would like. The panels are then stood up, clipped together, and a cementitious material is applied to both sides of the panel either with a pump or by hand.
SCIPs can be used on floors, roofing, patio decks, and stairs. SCIPs are said to save on concrete usage by up to 60% and to reduce the required rebar by up to 90%. In theory, SCIP panels are 4 feet wide and can be made as long as the project requires, but in practice, ISS usually doesn’t make them larger than 40 or 45 feet, so that they remain easy to handle.
How to Choose Which System to Work With
With all these options in the ICFs and Alternative ICFs universen available, choosing which system to work with can be difficult. When making your determination, manufacturer support and product availability are among the most important things to consider when weighing ICF systems options. Local or fairly local product support is said to be make-or-break for success, especially for someone new to ICFs. Once the concrete is placed, you can’t fix it without a lot of expense and effort, so if you don’t know what you’re doing there is plenty of room for error. Key is having local support from the manufacturer and from a knowledgeable contractor, a knowledgeable dealer, or company representatives that can provide hands-on, reliable support.
Credits for this article are shared with: ICF Builder: The Insulating Concrete Forms Magazine.
For Further Reading
• Concrete Construction Magazine – https://www.concreteconstruction.net/products/concrete-construction-equipment-tools/insulated-concrete-form-construction_o. Concrete Construction Magazine is a valuable resource for information on various aspects of concrete construction. Their online article discusses background, benefits, and technical aspects in the use of Insulating Concrete Forms.
• Insulating Concrete Forms Manufacturer’s Association: https://icf-ma.org/. The Insulating Concrete Forms Association is a trade association dedicated to promoting the use of ICFs in construction. Their website offers resources, technical information, and publications related to ICF technology. It can be particularly useful for industry professionals and those interested in the technical aspects of ICF construction.
• “ETW: Wall – ICF Wall Construction”, an article published by the Building Science Corporation, can be found at: https://buildingscience.com/documents/enclosures-that-work/high-r-value-wall-assemblies/high-r-wall-icf-wall-construction
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