I have a 40 year old house in fire country CA. Winters are 40’s for lows but snow is possible on occasion. Summers can go into 90’s.

I have already upgraded all windows and french doors with Marvin Infinity and exterior walls are currently 2×6 with fg batts and T111 siding.

For both heating/cooling efficiency and fire resiliency I am considering the external insulation approach with 2″ of Rockwool-type insulation and a fire resistant siding on a rain screen type assembly for the walls. That is the “simple” part.

1. Must I replace current siding or could I instead work right over it? It seems as though it has been serving as the WRB for many years and could continue doing so. Perhaps with a wrap or stick on WRB for air sealing?

2. Looking for details on window trim to bridge existing windows to new siding.