I intend to build a uPVC conservatory onto the back of the rear of our
semi. It needs planning permission because it is 4m deep.

One side wall of the conservatory will be adjacant to the 7' high
party-wall wall that runs the length of the garden, so it won't get
any sun and if I use a standard uPVC panel it will lose a lot of
heat. I could build a cavity brick/block wall instead, which would
solve the insulation problem, but it would make the conservatory
considerably narrower.

Is there a thin walling material, maybe 3" thick, that has high
insulation properties, and that might satisfy planning, that I could
use instead?


Thanks

Tony