[Paul C. Jesup]

I will tell you that double outer wall design is really a useless waste of money. If you want better energy conservation, buy a higher grade of insulation.

[alloysteel]

Not that walls cannot be improved. In order to place heavier (and continuous) insulation, there is a design, in which the thickness allowed for the wall is about 2" to 4" more than typical 2x4 stud design, in which either 2x6 studs are used, or staggered 2x4 studs spaced at 32", with one set of studs for the internal wall, and the other set on the external wall, offset at 16". The insulation is installed without breaks or gaps, with no direct contact between the interior and exterior wall surfaces. Thus no thermal conduction, and only limited internal wall convection.