Hi everyone, currently got an exterior cavity wall battened out with 2x2, filling in between the battens with 45mm celotex, just wondered if I should fill behind the celotex with something (silicone/foam?) before I push it between the battens. As the batten is roughly 50mm theres a give or take gap of around 0 - 5mm behind in certain areas if I leave the celotex flush. Alternatively I can push the celotex right back with will leave the gap at the front which would be directly behind the Plasterboard. Thanks any feedback is much appreciated.