Add top opening window

[Surftuzzer]

Hi.
On our windows, (upvc double glazed), the middle non-opening pane doesn’t have a small top opening window above it. Quite unusual.

Can we replace just the middle pane with one that does have a small top opener for venting? Or must we replace the whole window?

 

[Notch7]

New window required.

A top opener requires a transom between it and the glass below, a transom is a frame component that is welded in the factory, retrofit not possible