Abstract: Method and structure for insulating a building wall, ceiling, or like member supported by studs or rafters along various areas thereof, comprising the use ofan inflatable envelope of gas impervious material wherein the inflatable envelope includes at least two main wall portions;a first heat transfer barrier member substantially fully covering and secured to one of the main wall portions externally of the inflatable envelope;a second heat transfer barrier member substantially fully covering and secured to the other of the main wall portions externally of the inflatable envelope;a member separating the two main wall portions situated within the interior of the inflatable envelope and disposed between two main wall portions; anda valve for facilitating entry of an inflating medium into the inflatable envelope and retaining an inflating medium within the inflatable envelope; the method including installing the structure, securing it in place, and inflating the envelope.