So there's a couple of roof rafters running across the window opening!
If you have scaffolding up and don't ever intend cutting the rafters out, replacing it now with a top hung would mostly pay for itself next time you need a couple of slates replacing.
The current 24mm thick glazing should be a bit warmer compared to the old 16mm for next winter. Or at least just not leak whenever it rains.
2 or 3 from memory (fails to walk 5m to check). An epc cert guy was in yesterday and suggested just chopping the offending rafters, doubling up either side and top/toe it with some noggins.
So there's a couple of roof rafters running across the window opening!
If you have scaffolding up and don't ever intend cutting the rafters out, replacing it now with a top hung would mostly pay for itself next time you need a couple of slates replacing.
The current 24mm thick glazing should be a bit warmer compared to the old 16mm for next winter. Or at least just not leak whenever it rains.