What Are Insulating Concrete Forms?
Insulating Concrete Form Walls
The insulating concrete forms (ICF) building system (sometimes referred to as insulated concrete forms) uses Expanded Polystyrene (EPS) foam blocks that act as hollow forms into which ready-mix concrete is poured to build reinforced concrete walls. In contrast to the more traditional and labor-intensive carpenter hand-built timber forms or pre-made removable-form cast-in-place building systems that require removal of the metal or wooden forms after the concrete cures, ICF forms stay in place after the pour to serve as two insulating panels with high R-values for the life of the structure. The panels of both the ICF block and panel systems typically have a length of 48” with heights ranging from 12” to 18”. The cavity depth which controls the thickness of the concrete wall is typically offered in standard sizes from 4” to 12” with most manufacturers of ICF panel systems making provisions for larger cavity widths by the use of various extender adapters to increase the length of the standard ties. Some manufacturers of ICF offer both a block and panel version of their ICF so that builders who need toincorporate insulated pilasters and columns into their buildings, or to accommodate large, dense rebar concentrations, can do so without relying on make-shift measures.
The simpler to install block ICF systems are manufactured as hollow, open-ended EPS blocks that consist of two panels that are securely held together at a fixed distance using plastic or metal ties that are molded into the EPS block. In contrast, ICF panel systems consist of EPS panels and plastic/metal ties that are separately packaged and shipped to the construction site where they are assembled as the wall is erected . It is important to note that in both block and panel systems, the completely erected foam wall lends no structural value to the building on its own; rather, the structural strength of the wall is derived from the unparalleled strength of reinforced concrete that is placed inside of the foam cavities.
Assembly of the ICF panel system components typically entails firmly inserting the rigid, high-density polypropylene or polyethylene ties into the slots located on the inside of both panels and then aligning and firmly seating the resulting block onto the top of the previous row of blocks. It is important to note that in both block and panel systems the completely erected foam wall lends no structural value to the building on its own; rather, the structural strength of the wall is derived from the unparalleled strength of reinforced concrete that is placed inside of the foam cavities.
Typical ICF installations begin with stacking the ICF panels or blocks to form a wall during which time the horizontal reinforcing steel is laid inside of guides that are incorporated into the design of the ties. After the wall reaches a certain height, temporary bracing which is normally used for vertical and horizontal alignment of the wall is installed at regular intervals (usually every 6 to 7 feet) around the interior side of the wall. Depending on the ICF bracing used, this can also form the basis of a safe construction platform to work from for building taller structures. When the wall assembly is complete, vertical reinforcing steel is placed inside the wall cavities at intervals prescribed by the structural engineer. After finishing the top of the wall and preparing it ready for the pour, the wall is filled with ready-mix concrete in stages and mechanically vibrated throughout the pouring process to remove any voids caused by entrapped air. Once the concrete cures, the resulting wall is virtually impenetrable to physical or air infiltration and contains two layers of EPS insulation, one of the highest performing products on the market, that has a typical minimum insulation value of R-20 to R-25 (from both panels). Other major benefits provided by a solid concrete wall are its inherently high thermal mass, continuous EPS insulation with no thermal bridging, and extremely low air infiltration that eliminates drafts and cold/hot spots normally associated with stick-built houses. With some of the panel ICF systems, there is an option of using exterior panels that are thicker than the interior panels so as to optimize the benefit gained from the thermal mass of the concrete wall. Some of the block ICF systems offer a separate insulating panel that can be inserted behind the exterior panel inside of the block. This enhancement to the ICF wall’s thermal mass is something that is often required in Passivehaus or Passive House wall designs..
Since both sides of the ICF wall consist of a layer of exposed EPS foam (of selectable thicknesses with most ICFs), building codes require that interior and exterior finishes be applied to the respective sides of the wall. The most common interior finish is ½” drywall that can be directly attached to the EPS panels by using screws that are driven into the flanges of the ties that hold the panels together. These tabs which are typically manufactured from high-density polypropylene (HDPP) or polyethylene (HDPE) plastic are extremely durable and provide relatively high screw pull-out strengths. The exterior walls can be finished using virtually any product on the market from vinyl, stucco, and lap siding to stone, rock, and brick veneer. When attaching relatively heavier exterior finishes such as brick and stone, there are a number of ICF panel/block adaptations that enable the creation of ledges to support these heavier loads and various types of support systems that allow these features to be anchored into the concrete.
ICF for Floors, Decks & Roofs
As the popularity of ICF walls began to increase, many of the stakeholders in the ICF construction industry started to explore the prospect of using ICF floor and roof forms for residential and commercial construction. Building the entire structural shell using ICF forms would provide prospective building owners the opportunity to live/work inside a monolithic, reinforced concrete structure that exhibits amazing resiliency in the face of some of the most destructive forces of nature – tornadoes (250 mph+ wind speeds), hurricanes, earthquakes, wild fires, and floods. In addition to this exceptional disaster resistance, the convergence of ICF wall construction methods with the ICF floor and roofing systems extends the other amazing benefits of Insulating Concrete Forms to the entire structural envelope of the building.
Many of the manufacturers of ICF wall systems started to produce their own company-branded ICF decking forms, or forged partnerships with companies whose specialty was the manufacture of ICF floor and roofing systems. Two of the leading manufacturers of ICF decking systems, Insul-Deck and Lite-Deck ICF panels, produce steel-reinforced (2 beams/panel), EPS insulation boards that serve as permanent, stay-in-place concrete formwork for constructing floors, roofs, and other types of building decks. The integral steel beams serve as secondary shoring/formwork support and as a surface to which ceiling finishes can be attached. With a standard width of 24” (Lite-Deck also offers a 48” panel), these panels interlock with one another using a tongue & groove joint that aids in keeping the adjoining panels aligned and secure during the pour. These forms incorporate beam pockets (24” on center) into which ready-mix concrete is poured to form T-shaped beams that provide the primary structural strength for floors and roofs. Reinforcing steel is placed into both the T-beam pockets and the concrete slab formed over the top of the forms. Clear spans over 30 feet have been achieved with these decking systems depending upon live and dead loads specified in the structural design. Longer spans and/or higher loads can be achieved by increasing the height of the forms at the factory (supplemented by extra foam-blocks added to the top of the panels) which yields taller, stronger T-Beams. Using these concrete deck panels, roofs can be formed into both pitched and flat configurations. These panels are factory-cut to the exact length specified by the building plans, though it is preferable to also check measurements on site before ordering as occasionally on-site considerations lead to slight size variations.
Worth remembering is that choosing to design and build with EPS deck forming systems gives Architects and Contractors respectively major advantages over using more traditional concrete decking systems, some of which are the following:
- Reduces floor/roof mass dead load by up to 50%
- Reduces structural requirements for supporting foundations and walls
- Uses 50% of shoring as conventional slab forming methods
- 33% savings in reinforcing steel
- Up to 50% savings in concrete usage
- Fewer works-comp claims due to lightweight forms
- A proven, quicker and labor-saving deck forming system