Dear all,

Many thanks for the various replies.

Lobster was correct in the assumption that the Juliet balcony consists
of (large) inward opening casement doors, making secondary glazing
impractical.

I have already replaced all the suspect seals and there are no trickle
vents, so I think the next step is to get a few quotes for the cost of
new sealed units featuring the Pilkington glass mentioned. I'm sure it
will be eye-wateringly expensive!

Many thanks again,

Alex