Barry Young wrote:


2) I've heard that the larger the gap between the two "windows" is, the
better the noise reduction. As the window reveal is about 35 cm deep, I
could make the gap this size, making the secondary glazing flush with the
walls - would this make sense? Or should I aim for a smaller gap?

Yes, good sound insulation needs a much bigger gap than is desirable
for thermal insulation, but 35cm is probably much more than you would
need.

About 4 inches (10cm) is almost certainly enough. Interestingly, you have
the scope to make the secondary pane non parallel with the outer. This
is the approach used in sound studios to reduce resonances between the
panes and improves sound isolation even more.

If you can arrange it, and wouldn't mind the sloping appearance, making
the gap at the bottom (say) 10 cm and the gap at the top (say) 15cm
ought to be pretty effective.

Nick.