I now own what was my fathers 70's modular prefab basic box on top of rectangular foundation.
Basement plus one floor, approximately 1500 square feet.

so far I'm cleaning out the house and doing minor finishing ( preparing and painting 2 cm / 3/4" thick plywood floors to make rooms easier to keep clean )
I'm still concerned about the details of increasing the envelope performance.

I want to meet the German passivhaus performance standards and have minimum R-40 walls and R-60 roof.

I also want to design and build proper solar utility additions on the south and north ends of the house.

I'm in need of feedback and advise from the "pro's" ( and you are a "pro" )
What may I do that will increase the thermal performance a factor of ten which will not destroy the existing construction?

I'll be stripping the siding and roofing to expose the 2 cm / 3/4" sheathing and excavating the foundation to the footing and out around 1.5 m. / 4' .

I know a complete vapor barrier is needed and I'm concerned about mold and rot.

The wall cavities are currently insulated with 9 cm / 3 1/2" fiberglass

I've been thinking a lot about the possibility of having a positive pressure ventilation in the basement and a negative in house, balanced so the negative pressure in the house is great enough to keep vapor from entering the wall cavities.

Also thinking of a rigid 1" mineral wool "buffer" zone between the sheathing and vapor barrier that would allow "breathing" if the whole house is ventilated in a positive pressure.

Yup - - - I bit off a CHUNK ! ! ! and I really want and intend to do it right.

Hopefully by this time next year there will be accomplishments to talk about.

I should take this message and post it in a "green retrofit" tribe.