A building wall includes an exterior surface and an interior surface. The exterior surface faces the exterior of the building and the interior surface faces an interior room of the building. The wall has a total wall thermal resistance between the exterior surface and the interior surface. The wall includes a structural member positioned between the exterior surface and the interior surface, and the structural member is configured to bear at least a portion of a vertical load of the wall. An insulated composite wall panel is positioned between the structural member and the interior surface. The insulated composite wall panel includes a skin layer including glass fibers and a cellulose fiber insulation board attached with a resin to a first surface of the skin layer. The thermal resistance of the cellulose fiber insulation board comprises the greatest component of the total wall thermal resistance.