John Rumm wrote:
Andy Hall wrote:

50mm sheet would go some way towards modern standards. Installation
would imply 75-100mm reduction in room dimension once finished.
There are then the joinery (window reveals and skirting) and
redecoration issues (walls, floor coverings, ceilings) to address, so
although simple in principle there is a lot in the implementation.

Another interesting article would be how best to insulate period
properties without also destroying the period features. For example: how
do you insulate a solid brick wall that has ornate masonry and brickwork
on the outside, and complex covings, mouldings, picture rails and
skirtings inside.

You don't. Period. Haha.