Insulated concrete form
An insulated concrete form (ICF) is an interlocking polystyrene building block that can be formed into walls. Once formed, concrete is poured into the void inside for strength.
Contents
Dimensions
ICFs are available with different core widths which corresponds to the thickness of the cement once built. The core does not include the 2.625" of foam on each side of the core plus the dimension of any finishing product.[1] The width needed is determined by local build codes, however, generally:
- Below grade walls need a minimum 6" or 8" core[2]
- 4" cores have a maximum height of 10'
- 6" cores have a maximum height of 14'
- Typical residential construction use 6 or 8" core blocks
Thermal mass
The ICFs are left in place and provide continuous interior and exterior insulation with the interior insulation preventing the concrete's thermal mass from being useful for a passive solar structure. A curb block method allows for the exterior insulation to remain while the interior insulation is removed and replaced with a temporary wooden wall that is removed after the plywood sets.[3]
Alternatives to ICFs that may be better suited for providing thermal mass is board formed concrete, thermomass, and concrete masonry units. The interior polystyrene might be able to be removed by applying acetone to dissolve the substance.[4]