The cavity closer system is designed for use in masonry walls, timber and steel framed buildings to suit the cavity widths listed in the specification table. The system closes the cavity at window and door openings without forming a thermal bridge, provides a damp-proof barrier between inner and outer wall leaves at the point of closure, and can be used to establish the cavity width and to form an opening. It can be used in check reveal installations and can accommodate externally and internally installed windows. The closers are non-load bearing and window/ door frames must be fixed independently into the masonry. When the system is used with the head vent section and suitably sized trickle ventilator, it can contribute to satisfying the background ventilation requirements of the Building Regulations.