Hi there just after a it of advice going to be doing a bit of renovation and am looking at insulating the external solid walls as they are cold and sometimes get condensation. My method was to fix 25mm battons to the wall with a strip of dpc behind each one at 400mm centres then infill between with 25 mm celotex then a vapour barrier over the whole lot and finally plasterboard over the top. However after looking online I see some people and also on the kingspan website that there method is slighty different and they say about having an air gap so there method is the same as mine but instead of infilling the battons they screw the insulated plasterboard directly to the battons leaving an air gap behind but then kingspan also say it can be bonded directly to the wall with pu foam so surly this would mean There is no air gap or very little. I am confused about the air gap is it kneeded or not surly it would be better if the the insulation is touching the wall as i would be warmer thanks.