Insulated concrete forms (ICF's) give homeowners lots of design options including curved walls and soaring gables like this one.

ICF's, or insulated concrete forms, were developed more than 30 years ago as builders sought new ways to build tighter and safer homes. Approximately 100,000 concrete homes are built with ICF's each year and, according to the Portland Cement Association, the number of homes built with ICF's increases every year.

All-In-One Insulated Concrete Walls
ICF construction originated in Europe and features insulation on both the inside and outside of exterior concrete walls. It began to surge in popularity around 1990 as builders realized how many benefits and how few drawbacks there are to building with ICF's. In addition to being environmentally friendly, ICF homes are low-maintenance, thermally stable, and energy-efficient.

ICF's use high-density expanded polystyrene (EPS) blocks to build a form for poured concrete walls. Finished walls are typically eight inches thick, with four inches of concrete inside and two inches of foam on each side. The interior of the form is filled with cement using vertically placed steel rebar for additional strength. The forms are joined together with metal or plastic ties to make the required wall height and length, and corners are constructed with special corner blocks to maintain shape and prevent the cement from blowing out the form. The resulting wall is durable, soundproof, and super-insulated.

Panels, Blocks, and Planks
ICF components use three distinct shapes to make the walls—panels, planks, and waffle-like blocks that look like giant "Legos." Cement is poured into the form to produce one of three kinds of concrete walls—flat panel, grid, or post-and-beam. A flat-panel wall is much like a typical poured basement wall; a grid wall resembles a waffle; and a post-and-beam follows the traditional construction, but uses concrete instead of wood. All poured-wall types are sandwiched between insulated layers of polystyrene.

Insulated forms are tied together with plastic or metal straps to hold the interior of the form in place when the concrete is poured. Ties terminate on the interior or house side of the form with a fold-over or flat tab that serves as a fastening point for nails or screws when finishing the interior wall with drywall or paneling.

ICF Design Potential
Building with ICF's allows draftsmen, architects, or engineers almost unlimited design ability. Since the blocks can be carved and adapted into different shapes, each house can be customized without the "cookie cutter" effect that is so common in residential design.

Joe Lyman, executive director of the Insulating Concrete Form Association, points out the unlimited flexibility that builders and designers have when working with ICF's. "Essentially until the concrete is actually formed," he says, "the architect or draftsman or designer can have any design in the home that they want. If they are already putting up the forms and they want to double the window size, they can. They send a quick drawing back to the architect and he can design a "stirrup" to place in the mold to double its size and still carry the load from above," Lyman says. "You can do turrets, rounded walls, and curved walls, which are very popular right now, anything at all."

To modify the contour of the wall, the builder merely cuts out the back of the form, changes it to the specified curve or design, and glues in a new piece with a polyurethane quick-set glue. In five to ten minutes the form is ready with the change. "This really benefits the client because it is not just about square footage today, people also want the aesthetics. They want something different than every other house around them," Lyman says.

Strength and Indestructability
With concrete forms, design and strength form a perfect union. Because of their uprecedented strength, ICF homes can aren't limited to one-story structures. Two, three, four-story homes, or up to seven-story apartment buildings are possible when building with ICF's.

On multi-story homes, flooring constructed between each level can use conventional framing, engineered timbers, or decking forms designed for concrete floors. The house can also be topped off with concrete instead of conventional rafters or trusses, thus forming a virtually indestructible home. Fire, hurricanes, and tornadoes stand no chance of destroying a concrete house.