insulating concrete form (ICF)
Homes built using an insulating concrete form (ICF) system literally have the insulation built into the walls as part of the structure. This system creates walls that have a high thermal resistance, with R-values typically above R-17. Even though ICF homes are constructed using concrete, they look just like traditional stick-built homes.
Types of ICF systems
Insulating concrete forms (ICFs) are basically forms for poured concrete walls, which remain as part of the wall assembly. These forms also provide a backing for drywall on the inside of a home for stucco, lap siding, or brick on the outside.
ICF systems consist of interconnected foam boards or interlocking, hollow-core foam insulation blocks. Foam boards are fastened together using plastic ties. Along with the foam boards, steel rods (rebar) can be added for reinforcement before the concrete is poured. When using foam blocks, steel rods are often used inside the hollow-cores to strengthen the walls.
There are three basic types of ICF systems that use either foam board or foam blocks. A flat system yields a continuous thickness of concrete, like a conventionally poured wall. A grid system creates walls using a waffle pattern – the concrete is thicker at some points than others. A post-and-beam system consists of discrete horizontal and vertical columns of concrete, which are completely encapsulated in foam insulation.
Another ICF system uses foam board in the center of the concrete wall. This is often referred to as "tilt-wall" construction. The walls are poured in a form on a flat deck. After curing, the walls are "tilted" upright into position by a crane. Because the foam board is inside the wall, it reduces potential problems related to the foam's fire resistance, insect infestation, and moisture.
The foam webbing around the concrete-filled cores of blocks can provide easy access for insects and groundwater. To help prevent these problems, some manufacturers make insecticide-treated foam blocks and promote methods for waterproofing them.
Installation or construction of an ICF system requires a contractor who has experience with this building technique.