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.
Development
The first expanded polystyrene ICF Wall forms were developed in the late 1960s with the expiration of the original patent and the advent of modern foam plastics by BASF. Canadian contractor Werner Gregori filed the first patent for a foam concrete form in 1966 with a block "measuring 16 inches high by 48 inches long with a tongue-and-groove interlock, metal ties, and a waffle-grid core." It is right to point out that a primordial form of ICF formwork dates back to 1907, as evidenced by the patent entitled “building-block”, inventor L. R. Franklin. This patent claimed a parallelepiped-shaped brick having a central cylindrical cavity, connected to the upper and lower faces by countersink.
The adoption of ICF construction has steadily increased since the 1970s, though it was initially hampered by lack of awareness, building codes, and confusion caused by many different manufacturers selling slightly different ICF designs rather than focusing on industry standardization. ICF construction is now part of most building codes and accepted in most jurisdictions in the developed world.
Construction
Insulating concrete forms are manufactured from any of the following materials:
Polystyrene foam (most commonly expanded or extruded) Polyurethane foam (including soy-based foam) Cement-bonded wood fiber Cement-bonded polystyrene beads Cellular concrete
Reinforcing steel bars (rebar) are usually placed inside the forms before concrete is poured to give the concrete flexural strength, similar to bridges and high-rise buildings made of reinforced concrete. Like other concrete formwork, the forms are filled with concrete in 1-foot to 4-foot high "lifts" to manage the concrete pressure and reduce the risk of blowouts.
After the concrete has cured, the forms are left in place permanently to provide a variety of benefits, depending on materials used: Thermal insulation Soundproofing Good surface burning characteristics rating Space to run electrical conduit and plumbing. The form material on either side of the walls can easily accommodate electrical and plumbing installations. Backing for drywall or other finishes on the interior and stucco, brick, or other siding on the exterior Improved indoor air quality Regulated humidity levels and mitigated mold growth (hygric buffer)
Categorization
Insulating concrete forms are commonly categorized in two manners. Organizations whose first concern relates to the concrete classify them first by the shape of the concrete inside the form. Organizations whose first concern relates to the fabrication of the forms classify them first by the characteristics of the forms themselves.
By concrete shape
Flat Wall System
For Flat Wall System ICFs, the concrete has the shape of a flat wall of solid reinforced concrete, similar to the shape of a concrete wall constructed using removable forms.
Grid System
Screen Grid System
For Screen Grid System ICFs, the concrete has the shape of the metal in a screen, with horizontal and vertical channels of reinforced concrete separated by areas of solid form material.
Waffle Grid System
For Waffle Grid System ICFs, the concrete has the shape of a hybrid between Screen Grid and Flat Wall system concrete, with a grid of thicker reinforced concrete and having thinner concrete in the center areas where a screen grid would have solid ICF material..
Post and Lintel System
For Post and Lintel System ICFs, the concrete has a horizontal member, called a lintel, only at the top of the wall (Horizontal concrete at the bottom of the wall is often present in the form of the building's footer or the lintel of the wall below.) and vertical members, called posts, between the lintel and the surface on which the wall is resting.