Insulating Concrete Forms (ICFs) are stay-in-place formwork for energy-efficient, cast-in-place reinforced-concrete walls.
The forms are interlocking modular units that are dry-stacked (without mortar) and filled with concrete. The forms lock together somewhat like Lego bricks and serve to create a form for the structural walls of a building. Concrete is pumped into the cavity to form the structural element of the walls. Usually, reinforcing steel (rebar) is added before concrete placement to give the resulting walls flexural strength, similar to bridges and high-rise buildings made of concrete (see Reinforced concrete).
After the concrete has cured, or firmed up, the forms are left in place permanently for the following reasons:
- Thermal and acoustic insulation
- Fire protection
- Space to run electrical conduit and plumbing
- Backing for gypsum boards on the interior and stucco, brick, or other siding on the exterior
Types of systems
ICFs can be made from a variety of materials:
The majority of forms are made of foam insulation, such as expanded polystyrene (EPS), and are either separate panels connected with plastic connectors or ties; or pre-formed interlocking blocks connected with plastic or steel connectors or ties. Most forms have vertically oriented furring strips built into the forms on 6”, 8”, or 12” centers which are used to secure interior and exterior finishes.
Different ICF systems also vary in the shape of the resulting concrete within the wall:
- "Flat" systems form an even thickness of concrete throughout the walls, like a conventionally poured wall.
- "Waffle Grid" systems create a waffle pattern where the concrete is thicker at some points than others.
- "Post-and-Beam" or "screen grid" systems form discrete horizontal and vertical columns of concrete.
This method has several advantages compared to traditional building materials, especially in residential and light commercial construction. The advantages of structures built with this method include:
- Minimal, if any, air leaks -> comfort, less heat loss
- Superior energy performance -> Lower energy bills
- High sound absorption -> Peace and quiet inside
- Structural integrity -> Resistance to forces of nature
- Higher resale value due to longevity of materials
- More insect resistant than wood frame construction
- When the building is constructed on a concrete slab, the walls and floors form one continuous surface. This keeps out insects.
- Adding or moving doors, windows, or utilities is somewhat harder once the building is complete (requires concrete cutting tools).
- Cost - Depending on a model, home can cost anywhere from 5% to 15% more than a conventional wood built home.
The cost of using ICFs rather than conventional construction techniques is most sensitive to the price of labor, wood, and concrete. In the southern USA in 2006, a brick-clad ICF home cost around 5% more than a conventional brick-clad timber-frame home. However, the energy savings of an ICF home usually result in lower cost for utilities from Day 1 compared to most conventional construction.