Hi, I have a similar problem in that I had UPVC windows installed on my L-shaped bay on tuesday. When they installed the windows there was a 35-40mm gap at the top which was filled with Foam. Is this acceptable as I thought it should only be 20mm max. I had them stop work and called the surveyoer out and asked if the windows had been measured incorrectly. They fobbed me off saying that they could not determine the true height of the old PVC windows as it was hidden by the trim. They said everything would be fine once it was covered with the trim.

It may look ok but is this gap acceptable or will it cause problems with draughts in the the future?