The very first property I bought was a victorian mid terrace built in 1888. It had still elegant and generally functioning sash windows throughout the original part but the kitchen extension tacked on at the back ‘enjoyed’ side opening design, of single glazed aluminium from the 1970s. The trouble with both types, when we owned them, was their inescapable draughtiness and the condensation from the aluminium. Sash windows run up and down, with a slim but rough rope either side of the frame. Obviously over time, these dried up and a little candle wax rubbed over the tightest spots always seemed to cure the problem. The frames were still the original wooden ones and the catches to hold the windows shut had never been changed. Today this would be heralded as fantastic and worth keeping.
Many folk insist on ripping out the windows and doors when they buy an old property . The only way to keep the age and design integrity is to ask an expert in window replacements to do a proper survey to demonstrate how best to replace with designs exactly mimicking the original but minus the draughts, rattles and somewhat inefficient running mechanism, thus maintaining the authenticity as far as possible.