In message , Sacha
writes

We get buffeted by winds, though temperatures don't fall horribly low
over-winter, usually! But this house is Victorian and every interior wall
is solid, keeping the house very warm. The windows, OTOH, are those diamond
paned jobs and are not remotely well insulated. We can't use double glazing
and it would anyway look hideous. But interlined curtains and those nice
solid walls keep us very snug.

Why ever not?

We have simulated diamond double glazing in conventional timber frames.

Mind you, 25mm of Kingspan and boarding or render over 4" studwork walls
is not a recipe for low cost heating.

regards

--
Tim Lamb