Abstract: Double walled smokestack apparatus is provided in accordance with the teachings of the instant invention having substantially independent, load bearing inner and outer portions which are concentrically disposed to form a thermally insulating air space therebetween. This is achieved according to an exemplary embodiment by providing breeching and top cap arrangements intermediate the inner and outer portions which are configured in such manner to accommodate differential thermal expansion between the inner and outer portions without an attendant coupling of load. In addition, the inner and outer portions are fixedly interconnected proximate a mounting pad location where the moment of force of the inner shell is substantially zero.