The walls of my house have standard cavities, but where the walls form the
bay windows, the cavity drops to zero, ie two stretcher bond leaves butted
together. This obviously contributes to poor heat retention.
I want to insulate inside with something thin (ie low mu value).
I will strip of the plaster first. What is my best option?

I think it is common to put some sort of vapour barrier on top of the
insulation. why? A normal wall does not need it. I'm thinking polystyrene,
then plasterboard screwed to brick, then skimmed and painted. mositure does
not penetrate a regular plastered and painted wall, does it? Why should it
in this case?

Any how, what is my best approach? I don't really want to spend loads on
state of the art insulation. A freind has suggested 'bubble wrap' as a
possibility.

--
Mike W