PPS 6 Planning Archaeology and the Built Heritage·Page 60·E13
Window Repair and Restoration
Original windows can be repaired and restored to modern performance standards through seals, gaskets, and improved ironmongery rather than replacement.
Old windows were generally made of sturdy materials, they may look shabby and rundown and they may fit badly and admit drafts but nevertheless it is possible, more often than not, to repair and restore the original units. Repair rather than replacement should be the first aim in any scheme for a listed building. Original timber sliding box sash windows and casement windows can be fitted with seals, gaskets and improved ironmongery to provide a performance that will match any modern window type.
Source — /Users/richardhill/Documents/planning-arch-project/data/documents/regional/PPS 6 - Planning Archaeology and the Built Heritage.pdf