A popular method of insulating new build cavity walls is to fill the gap in between the two leaves, either by pumping them with EPS beads or by adding rigid board insulation.
In NI and ROI partial fill cavity wall insulation is widely considered to be the most traditional wall construction build up. The cavity is there to reduce the risk of moisture soaking through the external wall. In a bid to reduce heat loss, nowadays cavities are built wider than in the past to allow for insulation to be installed within them. By insulating inside the cavity you reduce the need to insulate on the inside of the house or externally.
