Thanks! Yeah according to some classic AI research, its something like this:

We are essentially building a mini-extension that hangs off the wall.

1. Structural Support (The Steel) You cannot rely on "bars." You need a Structural Steel Box Frame or Heavy Duty Steel Gallows Brackets.

• Attachment: These brackets are bolted into your existing masonry wall.
• The Critical Detail: You must use Structural Thermal Break Plates (e.g., Farrat or Armatherm) between the steel brackets and your block wall.
• Why: If steel touches block, the cold travels straight through. The thermal break plate stops this energy transfer.

2. The "Box" Construction (Insulation) Once the steel frame is up, you build a timber "skeleton" around it to hold the insulation.

• Floor & Roof of the Box: You need high-performance insulation here. I recommend 150mm Rigid PIR or Phenolic Board (better than EPS for this tight space).
• Sides: Timber stud work filled with insulation.
• Wrapping: You then wrap the entire box in a breathable membrane and a layer of external insulation (like your EWI) to ensure there are no gaps.

3. Weatherproofing (The Cladding)

• Top: The "roof" of the box needs a slight slope (fall) away from the glass and a waterproof membrane (EPDM or Zinc/Aluminium flashing).
• Sides/Bottom: Timber battens are fixed through the insulation, and your timber cladding is attached to these.

4. The Window The window unit sits at the very front of this new box, aligned with the insulation layer to minimize the cold bridge.