With increasing pressure to provide ever thicker levels of insulation there is concern that thermally upgrading conventional cavity walls, consisting of two leaves of masonry, may prove impracticable. Part 1 (4 pages) of this Good Building Guide highlights techniques and materials for insulating cavity walls. Part 2 (8 pages) provides guidance on how to reduce the associated technical risks. The guidance is for cavity walls having two masonry leaves; it is not suitable for timber-framed construction. NB it relates more to new-build housing than to retrofitting insulation.