Assembly and insulation of the openings
There is no more thermal bridges, neither apparent or hidden, the only sources of important losses are the doors, the French doors and the windows.
For the doors, it exists good isotherm doors with peripheral joint, but dut to the thickness we can't find any coefficient better than 1.2 W/m2.°C, that is to say hardly better than a good double glazing. A good solutiong used in northern country, even in Northern France, is to create an entrance airlock, which permitted, decades ago, to put down umbrellas and coats..
For the windows, we saw this, we can get down to 1.25. Thus we only can play on the surfaces : but you have to see clearly.
The important point when we can act and win a lot, it is the assembly.
In the case of outside insulation, you have to enlarge the boards by 5cm at eachsides to foresee an insulation of 5cm at the peripheral of the boards. The windows will thus be mounted tunnel-like showing at the surafce, and the polystyrene of insulation weel be against the fixed chassis of the openings. Putting cord of joint well adapted, there won't be any cm2 of wall in contact with outside air, neither a trickle of air which won't slip in the house.
The sketch below try to be as precise as possible.
The last critical point, but not the least, is the assembling of the threshold : it must be prefab and wrapped in a caisson made of styrodur or sort of, the French door or the windows, or door is posed on top of it with the intermediary of a joint half-tough, then sealed in "good position". The seal paws are directly sealed in the wall, at the shortest, like it was made before the poorly justified inside insulation technology.