Insulation is Cheap – Losing Heat isn’t.
Additional labor, Additional Framing Material, Additional Insulation will be necessary The energy-saving vastly outweighs the upfront costs of adding a second wall.
You will notice in this photo, the studs do not line up. This offset helps mitigate heat transference from one stud to the other (from inside to outside).
If you are in the beginning stages of drawing, Ask Your Architect about double exterior walls