A modular form system for constructing insulated concrete walls comprises spaced apart vertical frame members which include retention structures allowing for the insertion of spaced-apart rows of insulated panels to form an internal cavity into which concrete may be poured. The retention structures may include flanges on the periphery of the frame members and plates positionable in opposition to the flanges. The insulated panels are retained between the flanges and the plates.

A system and method for positioning and retaining an internal rebar skeleton for a concrete wall prior to pouring uses spaced apart vertical frame members having horizontal structures onto which horizontally oriented rebar can be laid and modular rebar retainers for positioning vertically oriented rebar in relation to the horizontally oriented rebar. The frame members may also include retention structures allowing for the insertion of spaced-apart rows of insulated panels to form an internal cavity into which concrete may be poured. External cladding is affixed to an external flange or sheath on the frame members with a thickness that creates a desired air gap between the external cladding and insulated panels. Frame members may also be laid horizontally across the top of a vertical layer of panels to form a base for a successive layer of vertical frame members and panels.