Working with award winning architects Hawkins Brown Associates LLP and Main Contractor Osborne Construction, 63 secondary glazed units have been installed during the remodelling and refurbishment of Plumstead Library, to make it more thermally efficient and to create quieter spaces for the local community user groups. The Grade II Listed heritage building required upgrades to the original single glazed metal framed windows which could not be changed, so a reversible adaptation was required by way of retrofitting secondary glazing. Two large sweeping bow windows facing the high street and many more openings across the building in various configurations required a sensitive and discreet treatment. They allowed light to flood the spaces, but did little to help the comfort levels of the spaces. Well sealed and tightly installed secondary glazing significantly improves the performance of original windows. If used in conjunction with metal framed openings, U-values of 1.9 and reductions of 45dB (if fitted with 150mm cavity) can be achieved. Series 10-3 pane horizontal sliders, Series 80-3 pane horizontal sliders and others, were used to complement openings in areas to serve as offices, a café and other functions. Each sweeping bay overlooking the high street was built up with seven Series 20 vertical sliders, transom coupled to seven Series 45 side hung casements. This configuration complimented the sightlines of the primary windows and allowed full access for cleaning, maintenance and natural ventilation.