Could I ask what the architects view was on internally insulating a solid (brick throughout?) wall. A scan back through the thread indicates rigid insulation and airtightness considerations - which would appear to fly in the face of the purist/Heritage-Nazi view which demands the wall be allowed breath.
To my mind, permitting the wall to "breath" isn't such an issue where the walls aren't exposed to weather - I've insulated such walling myself with no apparent detrimental effect, but I can see the sense where they are exposed.
How was this detail approached. I'm likely to trip across this issue myself again so any info to help decide my approach appreciated.
We only used solid in the new build extension, we used a breathable option in the original portion of the house.
If you use solid insulation you will get away with it for decades probably but by 50yrs the house will be in rag order with rotted floor joists, damp walls, plaster that needs replaced and crumbling brick work etc. you can look around town an see lots of examples where the building is in a terrible state of repair.
If you want a building to last do it properly at the start. I like to think of myself as the custodian of a building for future generations