The uPVC windows producers in Poland all recommend a gap of up to 20mm all around their windows' frames. It's sealed with the expanding foam after the windows have been bolted in the openings. The explanation for such a large gap is thermal expansion. However, when I popped into the display of the local producer/supplier of uPVC windows, I've noticed that the windows were fitted into the brick openings with practically no gap. So I wonder if such a gap is really needed ?? Any experts on thermal expansion of PVC out there ??
Chris