New double glazed windows don't block any traffic noise out?

[busbys1]

We recently had our sash windows removed and double glazed windows installed, there has been no reduction in the traffic noise, and the company say there is nothing they can do. There are no drafts etc, but you can here people walking past outside, any ideas what is causing this?

[busbys1]

Hi,
The windows are made of PVCu. The gap I'm not too sure but think it's 10-15mm. It's very old but the house is rendered but it's stone underneath. It's a local company, but quite a big one, advertises in the Scottish national paper. Paid in full. Did express concern, and they sent someone out, they took one of the windows out and used foam instead of whatever they had used the first time, still no difference. When we had the old windows, there was a secondary unit up and that did block the traffic noise to some extent, which is why I was expecting some reduction.

[buildersmate]

I think that you were poorly advised - sorry.
Secondary DG is well-known to be good at attenuating sound transmission, though its ability to prevent heat transmission is more limited (because the air gap is TOO big and it allows air flow to move between the two panes). So you have inadvertently switched a system that was quite good to one that is less good.
On the plus side, you will save more heat.
In sound attenuation, higher frequencies are easier to attenuate than lower - not a lot of help when lorries are thundereing past.
Some data on this here.
http://www.windowstoday.co.uk/sound-insulation .htm