Insulated concrete form

Insulating Concrete Forms (ICFs) are formwork for concrete that stays in place as permanent building insulation for energy-efficient, cast-in-place, reinforced concrete walls, floors, and roofs.

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 or floors of a building.

ICF forms are currently manufactured from any the following materials:

• Polystyrene (Expanded or Extruded) - most common
• Polyurethane (including soy-based ones )
• Cement-bonded wood fiber
• Cement-bonded polystyrene beads

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 concrete flexural strength, similar to bridges and high-rise buildings made of concrete (see Reinforced concrete). Like with other concrete formwork, the forms are filled with concrete in 1–4 foot "lifts" to manage the concrete pressure and reduce the risk of blowouts. After the concrete has cured, or firmed up, the forms are left in place permanently for the following reasons:

• Thermal and acoustic insulation
• 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 gypsum boards on the interior and stucco, brick, or other siding on the exterior

Benefits

Manufacturers commonly cite the following advantages compared to traditional building materials, especially in residential and light commercial construction.

• ICF structures are much more comfortable, quiet, and energy-efficient than those built with traditional construction methods.
• Minimal, if any, air leaks, which improves comfort and reduces heat loss compared to walls without a solid air barrier
• Thermal resistance (R-value) typically above 3 K·m²/W (in American customary units: R-17); 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.
  • Concrete and Polystyrene do not rot when they get wet
• Reduces HVAC operating costs from 30%-70%
• Construction methods are easy to learn, and manufacturers often have training available
• Designing and Building with ICFs help your construction project attain Leadership in Energy and Environmental Design (LEED) Green Building status.
• Insulating Concrete Forms create a structural concrete wall (either monolithic or post and beam) that is up to 10 times stronger than wood framed structures.

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 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-based materials like CMU, the insulating concrete form solution is usually less expensive.
• During the first weeks immediately after construction, minor problems with interior humidity may be evident as the concrete cures. Dehumidification can be accomplished with small residential dehumidifiers or using the building's air conditioning system.
• Depending on the form material, concrete mix and pouring procedures, honeycombing may occur during the pour, where gaps are left in the concrete. This can be resolved with the use of a vibrator, using free draining form materials or self-consolidating concrete, though the latter option is much more expensive and not necessary.
• With polystyrene based forms, the exterior foam insulation provides easy access for groundwater and insects. To help prevent these problems, some manufacturers make insecticide-treated foam blocks and promote methods for waterproofing them.

Construction costs

The cost of using ICFs rather than conventional construction techniques is most sensitive to the price of labor, wood, and concrete. Building using ICF can add 3 to 5 percent in construction cost over building using wood frame. However, the energy savings of an ICF home usually result in far lower cost for utilities 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 additional reinforcing steel directly around the window and large openings; and large openings reduce the materials needed (concrete, rebar, ICF).

• Typical new U.S. homes cost $60–100 per square foot. According to one estimate, building walls of ICFs adds $1.00-$4.00 to this figure. But since ICF houses are more energy-efficient, the heating and cooling equipment can be up to 50% smaller than in a frame house. This can cut the cost of the final house by an estimated $.75 per square foot. So the net extra cost is about $.25-$3.25.. According to a 2001 HUD report, the additional cost is $2.00-$4.00 per square foot

External links

• Insulating Concrete Form Association (North America)
• Insulating Concrete Formwork Association (UK)
• Green Building Talk- Interactive forum on ICFs
• US Housing and Urban Development on cost and benefit of ICF
• ICF Builder Magazine - Online how-to articles for ICF contractorsit:Insulated concrete form