ICF means Insulated Concrete Forms. It is premade forms that fit together like legos or large interlocking blocks. The outside of the form is flat sheets of foam insulation. These sheets are connected with plastic framework. During construction, the ICF blocks are fitted together, laced with rebar, and filled with concrete. The forms are insulated on the inside and the outside, providing high level of wall insulation uncommon in standard home construction. Because the ICF blocks fit together virtually seamlessly, there is very little air infiltration, increasing the effective insulation value.
The forms we used to build our house consisted of two layers of insulating foam approximately 2 inches thick, inside and out. The rigid insulation sandwiches a 6 inch thick layer of concrete. The Insulated Concrete Blocks measure roughly 16 inches tall by four feet long by 12 inches wide. They have an inner and outer plastic framework in the forms that stabilizes the form and provides strips that can be drilled into to mount drywall, cabinets, wood trim, and siding on the outside.
ICF can be used for basements, underground homes or entire multi-story homes. They can start at the foundation and go all the way to the roofline, as in our construction. Some builders use only insulated concrete foundation forms and combine them with other building methods above ground.