Thanks! And when I replace the glass, is it the same in reverse - i.e. do I need to use silicone or putty to secure the glass, then nail the verticals and horizontals?
I just bought a 1980s flat, and all of the doors have transoms/fanlights above them. I really like the fanlights, but they're all glazed with reinforced/wired glass, which I'd like to replace with some clear/frosted glass (which will have to be fire-rated, I assume). How do I remove the glass...