I have repurposed a 100-year-old divided light wood sash salvaged from a removed downstairs double-hung window to let light into bungalow gable. The photo shows a temporary install using resized 5/4 trim. Previously there was a louvered vent and I’ve removed the original cedar shakes to reuse later. Currently the sash is roughly screwed into a rough opening. The room is being converted to conditioned space and I’d like to have nicely trimmed out interior jambs in an insulated sheetrock wall. Basically I want originality on the outside and contemporary on the inside.

My choices:
    1.  Fabricate a traditional jamb with stops and sloped sill, set into rough opening with Zip flashing. This is directly below a roof overhang on the downwind side of the house and rain never hits the window. Keep exterior trim as-is and install from inside, caulk and insulate.

    2.  Buy a custom sized clad opening awning window and simply affix the old sash so that it covers the new sash.

    3.  Create a combo of the above by building a new frame and adding hinges to the top of the old sash. Probably best to open towards the interior with a simple prop to hold open for ventilation. Affix a screen just inside the exterior trim so it’s barely noticable.

I may want to install a permanent triangle shaped pane to the opening above the sash. Currently there is plastic sheeting in the space.  BTW, I’m not that concerned about having single pane uninsulated glass and hope the inspector does not object.

Observations and suggestions would be appreciated.