Existing dwellings can suffer from excessive air leakage which, if not treated, can lead to high energy costs, occupant discomfort from draughts & external noise, as well as a reduction in indoor air quality. To ensure that upgrading of external walls is as effective as possible, it is important to keep air leakage to an absolute minimum & preferably prevent it. Air leakage can be between the interior & exterior environments, as well as between different elements of the building envelope. Air leakage through the masonry wall occurs through cracks in the bricks, gaps where there is poor adhesion between the mortar & the masonry units, or diffusion through the masonry units themselves. Where the plaster has been removed & air leakage through the wall is thought to be excessive, it should be tackled before the SWIP IWI System is installed by applying a parge coat to the inner surface of the wall. As the insulation component of the SWIP IWI System is in intimate contact with the vapour control layer, air movement behind the system should be negligible. However, to prevent unwanted air leakage all junctions with other elements should be well sealed with particular attention being paid to the joints between the SWIP IWI System and window frames. The SWIP IWI System incorporates SWIP Vapour Control Layer which also acts as an air leakage barrier and enables the system to be integrated with other elements of the building such as ceilings and intermediate ﬂoors which is essential if air leakage levels are to be minimised or negated. In addition, SWIP Multi-Purpose Sealant should be used to seal electric sockets against the plaster-board, as well as all gaps around plumbing service penetrations. Any large gaps or penetration through the dry lining system can be sealed with expanding foam.