ICF
ICF (Insulated Concrete Form) is a building system where hollow EPS foam blocks stack like Lego, are reinforced with rebar, and are filled with concrete. The foam stays in place permanently as both interior and exterior insulation. A typical ICF wall has R-22 to R-28 effective thermal performance plus 6-8 inches of structural concrete in the middle, giving exceptional thermal mass, sound dampening, and storm/fire resistance. ICF is more expensive and has higher embodied carbon than wood framing but is durable and very tight when detailed correctly.