Dear All, we are doing a ground floor extension on the house (side and rear) next year. I wanted to ask what the norm is when insulating cavity wall (brick outside and block inside). The cavity is 100mm - is it normal to fill the cavity completely with insulation? architect is specifying full fill cavity 100mm dritherm 32. I have read (online, books, etc.) that it might be better to have 50mm insulation for example and leave a gap in the cavity in case water were to penetrate the outerleaf of the cavity wall. I just want to make sure that the specs are all in line with what the normal approach to doing a standard home extension is. Many thanks in advance for any replies and advice.