hi I am doing a extension and just laid the concrete slab after i done it some one said i should have put 25mm celotex or some kind of expansion joint all the way round against the exsisting house and new blockwork underneath the dpm. It was not on the drawing . However could building control make me take the slab up or is there another way round it. The floor make up is hardcore, sand , dpm ,concrete, insulation,screed Thanks for any help or advice