An insulated concrete form (ICF) is a lightweight hollow block. ICFs are designed as a stay-in-place formwork for poured-in-place concrete walls. Think of them as fancy LEGO blocks. The hollow block forms are typically stacked up, and concrete is poured inside. Although a typical concrete wall needs elaborate formwork to act as a mold, the ICF is the formwork. As you can see in image below, the ICF looks like a hollow mold.
ICF blocks are typically made of EPS, separated by plastic or metal spacers that hold the block together. The ICFs serve as a cavity for the structural walls of a building. Usually, reinforcing steel (rebar) is set into this cavity, and then concrete is pumped in. The concrete cures (firms up) inside the ICFs, which are left in place permanently, providing insulation. The result is a super-strong, very energy-efficient wall.
The History of Insulated Concrete Forms
Early ICFs first appeared in the late 1960s, with the growth of concrete construction. Conceived of by engineers as a “perfect” building material, ICFs combined simplicity, strength, and energy efficiency.
By 1972, a Swiss company developed Rastra, using recycled polystyrene and cement. This combination offered several advantages, including strength and ease of adding a stucco finish. Today, Rastra is one of the best-known ICF manufacturers available.
Production homebuilders have embraced the technology, and the use of ICFs has grown steadily, especially in areas where the strength holds the biggest benefit.
Although Rastra blocks use recycled polystyrene and cement, most of today’s ICFs are made of pure polystyrene, making them lightweight, easy to cut, and easy to stack.
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