Interior Furred Wall
An interior furred wall is a common method of achieving a cost-effective, energy efficient, highly airtight wall. A compromise between a conventional wall and a super-insulated wall, the “furred-in” wall improves your energy efficiency without the extra cost of building a REMOTE wall (which requires adding ⅔ the total insulation value on the exterior of the wall).
By adding 1.5 inches of foam board to the inside of the studs and vapor barrier, you greatly reduce thermal bridging through the wall and tighten the envelope by reducing penetrations through the vapor barrier.
While this wall system violates the ⅓ ⅔ rule for building in extremely cold climates like Interior Alaska, it can work because the exterior sheathing plane is vapor open and moisture can escape. Take care not to apply siding that would inhibit vapor permeability.