I want to knock a hole in an outside cavity wall and build a box on the outside of wall to take a woodburner. The stainless twin wall flue will then go up the outside of the wall and the stove will take up less internal floor space. Do I need to build the box with a cavity wall and if so what should I use to insulate the cavity? Also, do I need to line the inside of the box with a special liner and what should I use on the roof? I recognise that I will need to install a lintel in the opening.
I don't think there are any standards or regulations which can be directly applied to what you are proposing, I suspect it is against all regulations. Take a sketch of what you propose to your local BA and see if they can give you any advice.