External wall insulation (EWI) is fundamentally wrong. Insulation has to be primarily internal. For a passive house build, it has to be both and avoid all thermal bridging.
I live in a stone cottage with granite walls two feet thick. We took down all the plasterboard and lined the walls with Rockwool and then PU foam boards, mostly Kingspan. It is also important to insulate the floors and the internal walls. Ceilings should be insulated with thermal blankets and not double Rockwool. All heating and water pipes should be covered with thermal lagging.
Floors insulated (our dining area).
Walls double insulated.
Kitchen cooking area.
Again, double insulation.
And because of space constraints, double Cellotex.
So we went from this (and one sees the sum of all the sins hidden in old houses!) -
To this -
Almost there - about ten years ago.
The key is to do it room-by-room and get rid of everything. Whatever is there, from electrics to plumbing, from door lintels to chimneys, will be crap that just has to go! The results are cheaper and far better than putting totally ineffective toy cladding on the outside.
The total cost for the kitchen, without windows and fittings, was £3k. Today it would be about double that. Most other rooms were a few hundred per room - just plasterboard, battens, PU boards, electrics, rolls of Rockwool and plaster and paint and lots of Torx screws.
And before you ask - about three months for the kitchen-dining area and weekends only. And that was probably the hardest room to do. The living room was the most expensive because it included a stone fireplace from a quarry outside Harrogate, a fancy wooden floor and all sorts of fittings to convert it into a cinema with 7.1 sound from Genelec.
And that is the clue - when you decide to insulate a house, you get the chance to do all those other things that you wanted to do but would otherwise be too expensive/bothersome/time-consuming or whatever excuse you had for never getting round to do them.