I recently bought my first place - the greater part of a smallish house from around 1930, near Paris. The place has an energy rating of F, so, obviously, I have to do major work on improving its insulation. (I will also replace the gas heater by a heat-pump.) I will be insulating from the inside. Space is at a premium - each m^2 is very expensive (even in a relatively affordable suburb of Paris), and of course I have only so much space to work with.   The architect I am working wit