Figured I’d make a note on this… a couple of the louvers have cracked or broken. I noticed one this morning in the window on the northern wall, when we opened that window the offending louver quickly fell to bits.
I’ve since hand-manufactured a replacement out of some scrap perspex which should at least keep the rain out and might be less fragile than its glass original. (Thanks to @ltp for cleaning up my not-quite-square edge… doesn’t take much angular error with a tenon-saw and you find yourself about 5mm out!) A few other in similar condition on the eastern wall were pointed out to me.
The louver measurements are 580×150mm, for those who wish to produce more. The ~3mm perspex is fine thickness-wise, and has some give in it so hopefully shouldn’t crack/shatter so easily.