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Insulating concrete form

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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). The forms are filled with concrete every several feet in order to reduce the risk of blowouts. The foam on either side the forms can easily accommodate electrical and plumbing installations.

After the concrete has cured, or firmed up, the forms are left in place permanently for the following reasons:

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.

Benefits

Manufacturers commonly cite the following advantages compared to traditional building materials, especially in residential and light commercial construction. It needs to be said, however, that it is questionable what is meant by "traditional building materials"; this comparison apparently assumes different worst-case alternatives for each point.

  • Minimal, if any, air leaks, which improves comfort and less heat loss compared with walls without an air barrier
  • Thermal resistance (R-value) typically above 3 K·m²/W (in American customary units: R-17[1]), according to some manufacturers up to 10 K·m²/W[2]); this results in saving energy compared with uninsulated masonry (see comparison)
  • High sound absorption, which helps produce peace and quiet compared with framed walls
  • Structural integrity for better resistance to forces of nature, compared with framed walls
    • 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.
  • Reduces HVAC operating costs by up to 40%
  • Construction methods are easy to learn, and manufacturers often have training available

Disadvantages

  • Adding or moving doors, windows, or utilities is somewhat harder once the building is complete (requires concrete cutting tools).
  • Cost - Depending on design, an average home will cost about five dollars more per square foot more than a conventional wood built home. This usually amounts to about 5% of the cost of the home. For high-end wood homes this percentage decreases to about 2% or 3%. For high-end homes constructed of concrete the insulating concrete form solution is usually less expensive.

Construction costs

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. [citation needed] However, the energy savings of an ICF home usually result in lower cost for utilities from Day 1 compared to most conventional construction.

This also depends on the use of the ICF: Below grade, in most cases ICF construction will come in about 40% less than conventional (basement) construction because of the labor savings from combining multiple steps into one step.

Above grade, ICF Construction is typically a little more expensive. But when adding large openings, ICF construction becomes very cost effective. Large openings in conventional construction require large headers and supporting posts whereas ICF construction reduces the cost because all you need is a slightly bigger rebar schedule for directly around the window and large openings reduce the materials needed (concrete, rebar, ICF).

References

  1. ^ "Insulating Concrete Forms". EERE Consumer's Guide. U.S. Department of Energy.
  2. ^ "Isorast 2000 Icf Building System". Alibaba Group.
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