On Mon, 09 Jul 2012 09:20:32 +0100, ss wrote:

Am I likely to gain much by way of heat loss and sound insulation or
would it not be worth the effort?

As you already had DG there won't a be a big a saving on heat as going
from SG to DG. probably not a lot gained for sound either. The big snag
is that you will never get the gap between the secondary and main glazing
properly sealed an you will get condensation in that gap. This will lead
to rotten timber frames or mould/algae on plastic.

And what do you mean by "traffic noise" a busy main road/motorway at
50yds or the odd passing car on a quiet residential street?

--
Cheers
Dave.