Just about to have some new plastic DG fitted. Total fit around large
house.

The guy from the company noticed that some of our DG windows (all of
softwood, 'cos that's why we're replacing) said, "Where you have
trickle vents already fitted, we'll have to do the same".

We had an extension added about 12 years ago and the DG on wood frames
in that part of the house all have trickle vents. The rest of the
house has older DG on wood, done 25+ years ago without trickles.

Questions:
1. Is it correct that he has to put trickles where they are already?
2. Why, if this is a good idea, isn't he insisting that they are
fitted in the older part of my house?
3. Why are trickle vents a good idea given that:
a. no condensation in the older part of the house which is
without them, and
b. if I am spending so much money to save energy, why would I
want to have a route for drafts
back into my house?

I think the expanded foam canister beckons.