Insulating 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 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 in 1-4 foot "lifts" to reduce the risk of blowouts like with other concrete formwork.

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 foam on either side of the forms can easily accommodate electrical and plumbing installations.
• 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:

• Expanded polystyrene (EPS) - most common
• Extruded polystyrene
• Polyurethane
• Cement-bonded wood fiber
• Cement-bonded polystyrene beads

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); 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 does not rot when it gets wet
• Reduces HVAC operating costs from 30%-70%
• Construction methods are easy to learn, and manufacturers often have training available
• ICF structures are much more comfortable, quiet, and energy-efficient than those built with traditional construction methods.
• 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 monolithic concrete wall that is 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 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.
• 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.

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. 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 ICR: 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).

• Typical new U.S. homes cost $60-100 per square foot. 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 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.

External links

• Insulating Concrete Form Association (North America)
• Insulating Concrete Formwork Association (UK)
• ICF Info by the Portland Cement Association
• PATH Tech Inventory: Insulating Concrete Forms
• PATH Case Study Using ICFs in Lubbock Texas
• Concrete-Home.com - Online Forum on ICF Construction
• ICF Builder Magazine - Online how-to articles for ICF contractors and do-it-yourselfers
• Green Building Talk- Interactive forum on ICFs