Double glazing, the type used to keep houses warm, does virtually nothing to create any form of sound proofing. To provide any measure of sound proofing the air gap needs to be about 10 cms........
Double glazing does virtually nothing?
Gatwick and Heathrow have schemes to subsidise instalation of double glazing as part of their residential noise insulation scheme.
BAA Heathrow noise website: FAQ's - night noise
One of the options is
"A fifty per cent contribution to high specification double glazed PVCu replacement windows, specially designed to reduce noise levels"
Mickjoebill