This is a replacement sash model GVA with a broken glass panel. These are the older Velux conservation windows. My feckless son left it open in a storm and it slammed shut and broke the glass. No longer required. These simply attach with one screw ( not included) on each of the two hinges at the top of the opening. The window fits diagonally through the existing hole then can be simply attached with 2 screws. No scaffolding required! As per photos, the glass is broken but is easy to get replaced at a glazier. I Have put tape across the broken glass.
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